Professor Ross Taylor, geochemist

Professor Ross Taylor

Professor Ross Taylor was born in Ashburton, New Zealand in 1925. He was educated at Wakanui Primary School and Ashburton High School. In 1948 he received a BSc and in 1951 an MSc Hons, both from the University of New Zealand. In 1954 he received a PhD from Indiana University. From there he went to Oxford University where he taught and worked with Louis Ahrens, setting up a spectrograph laboratory. In 1958, Professor Taylor took up an appointment as senior lecturer in geochemistry at the University of Cape Town, South Africa. In 1961, he moved to the Australian National University as senior fellow in geophysics. In 1962 he was appointed as a professorial fellow in the Research School of Earth Sciences, also at the Australian National University. In 1969 and 1970 Taylor was responsible for carrying out initial chemical analyses of lunar samples brought back to Earth by Apollo 11 and 12. Taylor's work with lunar samples led to his interest in the evolution of the Moon. More recently, he extended this interest in planetary origins to look at the evolution of the solar system.

Interviewed by Professor Bob Crompton in 2000.



Professor Ross Taylor is a New Zealander by birth. Having majored in both chemistry and geology, and completed an MSc at the Christchurch campus of the then University of New Zealand, he went on to the University of Indiana to take his PhD in geochemistry. He was then appointed to the staff at Oxford, and soon secured a tenured position. A more senior appointment lured him to the University of Cape Town, where, as in Oxford, he established a laboratory for the analysis of trace elements in rocks, using emission spectroscopy. He was also given the responsibility of establishing the Geochemistry Department at that university.

After some 10 years in the northern hemisphere, he headed closer to home again, having accepted John Jaeger's invitation to come to the ANU, where he remained until his retirement in 1990. Again it was his role to establish a laboratory for trace element analysis of minerals, first using emission spectroscopy but later spark-source mass spectroscopy.

Through his wide-ranging studies of the evolution of the Earth's continental crust and of lunar geology, Professor Taylor has become an internationally recognised and honoured expert in his field of geochemistry. An early high point was his work on the origin of tektites, to be followed by his highly acclaimed studies of the geology of the Moon. He was one of a team of 12 international scientists invited by NASA to make a preliminary analysis of lunar samples recovered by the Apollo 11 and 12 missions. This was followed by his appointment as a NASA principal investigator, and in that role a further 20 years' study of the composition of lunar rock samples. It culminated in his proposal of a model for the geochemical evolution of the Moon that remains to this day as the standard model.

His work goes on since his retirement, and we will hear more about that in this interview. His scientific achievements are published in over 200 papers and in seven books.

The international recognition of Professor Taylor's work includes a DSc from Oxford and election as a Foreign Associate of the US National Academy of Sciences. He is also an Honorary Fellow of the Royal Society of New Zealand, and the recipient of medals and awards from a number of learned societies. And above our heads circles an asteroid designated 5670 Rosstaylor, named in his honour.

In this interview we will follow his distinguished career from its beginnings in New Zealand right up to the present day, when he continues to make important contributions to the subjects which fascinate him.

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Taking off from a good background

Ross, perhaps you would start by telling us how your family came to be in New Zealand, where you were born, and about your early childhood.

My grandfather emigrated from Northern Ireland to New Zealand as a boy of about 20. After goldmining and a few other adventures along the way, he set up a farm which is now in the fifth generation of the family. He had 13 children altogether, my father being the youngest. My father also became a farmer and so I was brought up on a farm, which was a very good, satisfactory background – very peaceful, and you learn the virtues of hard work.

My family insisted that my two brothers and I received a good education. My mother had been a primary school teacher and so she coaxed us along in school. We went to the small country school, which had about 40 pupils separated into two class groups of four years. The two teachers seemed to cope quite all right with this.

I believe you had a brush with appendicitis in those early years.

Yes, at the age of 10, I developed it very quickly overnight. The doctor came down from the local town on a house call, had a look at me and went away again, but then in response to calls by my mother he came again and took me in the back of his car up to the hospital. Those were the days before penicillin, and the appendix had already burst, so I was in trouble I didn't know about. Anyway, he operated and being a good doctor he managed to save me from 'another place'.

When you went on to high school, did any mentors particularly excite your interest in science, or was that almost a natural bent?

All the teachers at the local high school had Masters degrees from the university and the quality of the teaching was really very high: one received very good education in English and Latin, maths, and so on. Our Scottish chemistry teacher was very good and he taught us classical chemistry very effectively. I always liked chemistry, but I couldn't say I was particularly excited by that more than anything else. I did receive a science prize in the sixth form, however, which triggered me into doing science later.

During this time the Second World War was on, preoccupying almost everybody's attention. Like almost all of my contemporaries I was very keen to become a member of the Air Force – in retrospect, that was exceedingly dangerous. We were obviously seduced by the propaganda. I inherited a certain distrust of these large organisations from my father, who had been in the First World War. Having survived the disaster at Passchendaele, he had lost any faith he might have had previously in the British High Command's ability to conduct battles. But being so preoccupied I did enlist in the Air Force, even though the war was coming to an end – and my elder brother was an Air Force pilot, flying Sunderlands in the Atlantic.

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Building a chemistry base

After that, it was on to the University of New Zealand.

Yes. I thought I had better do Science at the university. I'd never thought to do Arts but I had some inkling of doing Law. Fortunately, I chose to do chemistry.

In those days, it was just one university, wasn't it?

Yes, with several different campuses. I was at Canterbury University College, in Christchurch: a very interesting place, with about 2,000 students and a highly qualified academic staff for such a small university. One lecturer in particular was Karl Popper, a refugee from Vienna who somehow spent the war years in Christchurch – the University of London seized him after the war. I attended one or two of the lectures he used to give, and I regret not having heard more of them. Our geology professor, Professor Allen, was fascinated and became a friend of Popper's. He used to give us secondhand Popper in his lectures and I thought, 'This is what I've come to a university to find out about.'

The chemistry and physics were very well taught, very efficient, but geology fascinated me more, particularly perhaps because of this philosophical bent and also because it opened up the vista of the geological history of the planet, which I had not really known anything about. I'd always been interested in history (which I still read for pleasure and also as a reminder not repeat the mistakes of the past) and so this led me to major in geology as well as chemistry.

There were a couple of well-known physicists at the university, MacLeod and White. Could you tell us something about them?

Duncan MacLeod was the acting professor. He was famous because he had invented the MacLeod gauge. He was a very good lecturer but hopeless at doing mathematics on the blackboard. He always got it wrong, and all the students used to complain. Realising it was all in the textbook anyway, though, I used to take the textbook to the lecture and follow what he was talking about. His explanations of gas laws and wave theory were very high quality, and I learned a lot.

Professor Fred White had been snatched off during the war to CSIRO, in Sydney. His name was still on the door and his imminent return was eagerly awaited, like the Second Coming, but he never made it back.

Chemistry won out over geology for a while, I understand, because you went into a chem lab in a freezing works as a holiday job. Did you learn anything there?

Yes, indeed. There was a lot of pressure in the laboratory, which looked at the by-products from the freezing works, such as tallow and blood-and-bone. We were the central lab for half a dozen freezing works around New Zealand, and every morning, in the mail, samples came in. The rule was that the results went out at 4 o'clock in the afternoon, so I had to work quickly and accurately and to get the right answers. It was in great contrast to the usual dishevelled state of university laboratories, and I actually learned to do chemistry properly there. I worked at that, off and on, for a couple of years. It was a good training ground, good discipline.

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Applying trace element chemistry to geology

Nevertheless, you went on to do an MSc in geology. Who was your mentor then?

This was Professor Allen, Popper's friend. It involved a large amount of field work and mapping large areas of unmapped country, and I learned a great deal about the difference between doing geology in the field and reading about it in the university. The thesis was titled 'The Geology of the Stonyhurst Area of North Canterbury'. One had to wander all over that hundred square miles – a very interesting area – mapping and unravelling the structure. One of my pieces of unfinished business is that I have never actually published the thesis.

It was very much straight geology, not geochemistry, wasn't it?

It was classical geological mapping, but very good training. In geology, sampling is always a problem. There are so many variables, so many possibilities in picking up samples. The Earth is so big, relative to what you can analyse in the laboratory, that you have to be very careful in the selection of samples and to have almost an intuitive field sense for what is critical, which many geologists develop as a result of this work. Looking at the country, you must be able to decide which area to get the sample from.

You went off after that to do a PhD in the United States. Where did you go, and why, and what did you do there?

After the Masters degree I wanted to get into university teaching. Research hadn't really come into it very much at that point. Looking around, I realised I needed to get a PhD. The tradition was to go to England, usually to Cambridge, to do a DPhil, but I could see a lot of very good geology coming out of America. One of my former teachers from Christchurch was over there – he had been a PhD student with Goldschmidt, the founder of geochemistry, but because of the war he had left Norway for Sweden, eventually returning to New Zealand, where I met him. By this time he had gone to Indiana University as a professor. I wrote to him and he said, 'Well, why don't you come here? You can do a degree in geochemistry.' He suggested I do some work on trace elements, as they had a very good spectrographic laboratory set-up at Indiana. None of this was then available in New Zealand.

Chemistry interested me, but from the way that chemistry had been taught to us – it was a very cut-and-dried subject – everything seemed to be done and I could see very few new openings. And the field geology I had been doing was standard field geology that people had done for 100 years. Of course it's much easier to see all this in hindsight, but I had an intuitive feeling that it was better to go into new fields, and geochemistry was obviously opening up. So I went off to Indiana and learned how to operate spectrographs and do trace element analysis, which made sense by putting together the chemistry and the geology as geochemistry.

How old was the field of geochemistry, Ross, when you went to Indiana?

It started about 1930, with Goldschmidt working in Göttingen and subsequently in Oslo. The first textbook appeared in 1950, just a year before I got to Indiana. Then my first job as a graduate student was to proofread Brian Mason's new textbook, and I realised I was suddenly right up to date. I've always told my students subsequently to pick the right PhD supervisor, because without much effort you find yourself up at the cutting edge of the subject.

For my thesis I worked on the trace element chemistry of the Banks Peninsula volcanoes, immediately adjacent to Christchurch. I collected a whole set of samples and took them over to Indiana to work on the chemistry of them. Mainly that taught me the techniques: I thought I made rather more geological breakthroughs in my Masters degree thesis than in my doctorate thesis – which did get published, about 20 years later. But this was still trace element chemistry on geological materials, rather than geochemistry.

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Trace element emission spectroscopy, in a new laboratory

After you graduated in 1954, you left Indiana for Oxford. Who influenced that?

Curiously, there was again an Oslo connection. Brian Mason went off to a museum job in New York, having recruited one of his friends to fill in for a couple of semesters at Indiana: Henrich Neuman, a mineralogist from Oslo – a very sophisticated, educated European, very nice to talk to. I was rather aghast when he suggested I should go to Oxford, which had Bill Wager, who amongst other things had almost got to the top of Mount Everest in 1933 and was a geologist, and Louis Ahrens, who was the leading expert (having just published a textbook) on trace element spectroscopy. This was obviously a glittering place to go to, and it was with some fear and trepidation that I wrote to Wager. I got a very nice letter back offering me a demonstratorship, like a junior lecturer job, there. I discovered subsequently that Neuman had written independently – you learn some of these things later on in life.

What was the mix – mostly lecturing, or some lecturing and some research?

It was a fairly heavy lecturing load, but at the same time Ahrens wanted a laboratory set up. He'd arrived there from MIT only a year or so before. My job was to set up their spectrograph (in a bare room) and get the laboratory properly organised and operating. The whole set-up was a bit primitive, but it worked. Hilger spectrographs were actually very good instruments. And so I had teaching, tutorials and running this lab, which had a lot of students through it. I was very busy.

In a way you were lucky to be thrown in at the deep end to teach, which is so necessary in an academic job, as well as to establish a laboratory, which was useful for your future career.

Well, yes. I wasn't married at the time, and so one just worked days, evenings, weekends. Actually, I needed a fair bit of time to do all these things.

After about 18 months in Oxford, you were offered a tenured post which you held for your remaining years there. It was a real feather in your cap, to get a tenured position so soon.

It was certainly very nice, and I left only with a great deal of regret. I still have a very soft spot for Oxford, and the tie I am wearing is the Geology Department tie.

Did you meet and marry Noel in Oxford?

Yes. She had come from West Australia and was doing a PhD with Dorothy Hodgkin, the organic crystallographer, on a very complicated organic crystal structure. In those days they had to go down to Teddington to run the stuff through the National Physical Laboratory's very primitive computers. Nowadays it's a routine thing, but then it called for a great deal of judgment: if you were not on the right track you wasted months. We were married in 1958, just before leaving Oxford.

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Teaching and practising geochemistry, in a second new laboratory

Where next, and who was your link this time?

I went to Cape Town, where by then Louis Ahrens was a professor in the Chemistry Department. He was South African by birth and very much attached to the country. Cape Town is a beautiful place, if you exclude the politics, and he found the living there much more to his liking than in either MIT or Oxford. Ultimately, though, he might have been much better in the American scene, where he had real competition. He was arguably the leading geochemist in the younger generation, and South Africa was too much of a backwater for him. He was much too big a fish in that small pond; he should have stayed where the action was.

What were your responsibilities in Cape Town?

I moved into the Geology Department and, with a couple of assistants, set up a separate small Department of Geochemistry. We taught courses in geochemistry and again I set up a laboratory, around another Hilger spectrograph. Eventually we got new buildings and so on, which also kept me very busy for the next three years. Having developed the techniques of trace element analysis, I looked around for interesting projects to work on. I started to work on tektites and I was working on minerals as well – feldspars, particularly, and various rock types. And then there were students with their research projects. So there were a whole lot of things going on.

Were you now really beginning to use chemistry for geological purposes?

Yes. It was rather difficult getting good science data from these instruments, but once you had all the techniques straightened out you could look at some of the many geological problems. I enjoyed the fact that almost everything you looked at was new – nobody had done it before.

Once you have worked out the compositions, very accurately, what does the geochemistry then tell you about the geology?

Until you know the actual composition of the rocks, you have no idea where they or the material in them came from. As you delve into the history of rocks on the surface of the Earth, finally you discover that the elements in them have come through many cycles of repeated extractions from the interior of the Earth. You can then map all these things through trace element chemistry – and also with isotopic systems, which I never really got into but which tell you the ages. It just opens up an entirely new approach to the evolution of the Earth that had formed.

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A university incensed

You were in South Africa in the late '50s, very early '60s. Political topics such as apartheid became prominent worldwide later on. Were they already to the fore in South Africa itself?

Yes, very much. The notorious Nationalist government, having got into power in 1948 by defeating Smuts, had set about implementing their policy of apartheid. One realised that the Boer War was still going on in South Africa – these, effectively, were the Boers. There was still a profound division between the English and the Afrikaners, to the extent that Cape Town was an English university whereas Stellenbosch, 30 miles away, was an Africaner university where Afrikaans was spoken, and there was almost no contact between the two. The government decided that there should be complete separation of the races and started carving up the multiracial districts in Cape Town and segregating people, incensing the university by saying it could not have black students any more.

Unlike many demonstrations in universities, this was the students and staff together, rather than the students against the staff, wasn't it?

Very much so, yes. Everybody was united on this. We had many protest meetings, and signed petitions, and every few months there was uproar about what the government was trying to do next. Eventually separate universities were set up for the coloured and then the black population. Everything was rigidly divided by race.

I thought this was a crazy situation. Many of the South Africans, having grown up with it, accepted it to some extent. However, I found more discussion on these matters at the University of Cape Town than in America, Oxford or Canberra. What constituted university freedom, what universities were supposed to be doing and the question of university independence were endlessly discussed, and pamphlets about them were written and distributed around. So there was a very active political environment, totally opposed to the government policy.

The university succeeded ultimately by various tricks: black students were allowed in under the grounds that there were no other facilities in the country where they could be taught particular subjects, and so on. One way and another, the university survived with probably a 10 per cent black population, until very recently.

One good thing about being in a university is that you are portable. I thought, 'Well, I don't really have to live in this community. I don't have to put up with this and I wouldn't want to bring up a family in this environment.' One could see disaster of some sort coming – within about five years, I thought, but curiously enough the country remained in that condition for the next 20 or more years.

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Moving on to spark-source mass spectrometry, in the next new laboratory

Who drew you further south?

I received an offer from John Jaeger, who was setting up the Geophysics Department in physical sciences at the Australian National University and was interested in setting up trace element geochemistry. I had never met Jaeger, but he had offered a professorship in geochemistry to my mentor in Cape Town, Louis Ahrens, who after a lot of soul-searching had turned it down. I let it be known that I would be interested in coming here anyway, so then Jaeger offered me a job. I thought it was too good an offer to turn down – but I'd no sooner arrived here when I received an offer of a Readership in mineralogy at Oxford, one or two steps up from my old job, basically. I pondered for a long time before deciding to stay here.

Chewing the end of your pencil, no doubt! What were your first responsibilities here?

I set up another laboratory, with a spectrograph in it. Fortunately, as a student in Indiana I'd learnt the nuts and bolts of doing this, and by now I was used to it. But here, in 1961, it was easier because money was much more readily available, so I could buy the really fancy stuff. Where always I had struggled on with hand-to-mouth funding – a few hundred pounds a year – here I could buy the most expensive equipment. It was very nice to get the right stuff at last.

I worked on the spectrographs but we were reaching the end of what we could do with them. Their detection limits were only perhaps a part per million for many elements and there were a lot of elements we just couldn't reach. We needed some other technique. There were various options available, such as neutron activation, but then I discovered that spark-source mass spectrographs were being built in the solid-state electronics industry for trace element analyses of semiconductors and so on, and I decided we could adapt that instrument to do geological samples. They were not so very different.

I'm only used to gas mass spectrometers. How does a spark-source work?

In basic spectrographic analysis you have a direct-current arc and a powder; you ignite the sample and you look at the atomic spectra. In the spark-source, the sample is compressed into small electrodes and you use a 25 kV spark which erodes the sample and ionises the atoms. These then go into a mass spectrometer and you get a mass spectrum at the end. The one we had was a nice big double-focusing mass spectrograph, which used a photographic plate. You got the whole periodic table out on it in each photographic plate. For various reasons we could only really look at elements above about mass 80, but that was the area which was very interesting, the area we couldn't reach with other techniques. The lighter elements were mostly easy to reach by spectrographic techniques, X-ray fluorescence or various other techniques.

Just because they were more abundant?

Yes. These were less abundant elements, such as the rare earths, uranium, thorium, hafnium, tungsten – lots of nice elements which you can do a lot with geochemically, once you have established the precise analyses. I have brought with me four such plates: one from a lunar sample, one from a tektite, one from a sample from the deep crust, and one of loess, the windblown sediment of which the most famous example is the Yellow River regions in China – very thick deposits of windblown clay from the Ice Age. Together these give an average sample of the upper crust of the Earth, which is one of the things I was always looking for. My students mounted this little exhibit and gave it to me at my retirement. It remains one of my treasures.

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Conflicting theories about tektites

At the ANU you pursued further your interest in tektites, didn't you?

Yes. I'd been rather an earthbound geologist until, when Harold Urey was on sabbatical leave at Oxford, he used to come over and talk to the Geology Department people at morning tea about the Moon and tektites and all sorts of other things. That triggered my interest.

Tektites are tiny glassy objects which you find scattered on the surface of the Earth. I have here one with a little flange on it and one looking like a teardrop. They result from localised meteorite or asteroid impacts and occur in only four or five localities,. The ones in Australia, for example, cover most of the country, as in most of Indonesia and a lot of South East Asia, so these so-called strewn fields of tektites are very widespread. But they are still localised.

I understand that there was quite a heated controversy on the origin of tektites. What were the two conflicting theories?

Harold Urey had at that time woken up interest in the Moon. His great contribution was to wake up interest in the chemistry of the solar system as opposed to its dynamics. So people started looking at tektites. There was no obvious source for those that were found, so the idea arose that they had perhaps been blasted off the Moon by, say, meteorite impact or perhaps volcanoes. Some people had even worked out which crater on the Moon they'd come from. Of course, if they were samples from the Moon, they would be of extraordinary interest. Anyway, an argument broke out whether tektites were from the Moon or from the Earth. People very rapidly split into two camps, and at some of the meetings we had some rather heated exchanges.

The advantage of the trace element spectrography was that you saw data for a lot of elements. I had done a lot of analyses of tektites, looking very carefully at them and comparing spectrographic plates of granite and basaltic lavas on the Earth with those of tektites, and they seemed to me to be very similar to terrestrial rocks. So in 1963, at the University of Pittsburgh – one of my first international meetings on tektites – I got up and gave my paper saying what I thought. And people said, 'Oh, you're in the terrestrial camp, are you?' I said, 'No, I'm just trying to understand where they come from.' One was put willy-nilly into this camp, and the lunar people then attacked one quite viciously, saying, 'These are perfectly reasonable samples from the Moon.' This controversy went on for several years, right up until the first Moon landing.

In 1969 I went to a meeting on tektites held by Corning Glass, who had research laboratories to study glasses. Tektites are extremely dry, with almost zero water content. This fascinated the glass chemists, because in industry it is very difficult to get the final water out of glass. At the end of the meeting Brian Mason – my PhD supervisor, who was there as chairman – said, 'Well, in about three months we're going to know the answer to this, so why don't we take a vote?' The vote was 50/50 for lunar versus terrestrial origin, and to this day I retain a residual distrust of people who voted for the lunar origin. But it was a very vicious scientific controversy, because obviously the stakes were quite high. I was a bit astounded to find myself in the middle of all this, because by about 1962 I had firmly come to the conclusion that they had to be terrestrial rocks.

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How and where tektites originate

What is the origin of tektites, then? How do they come to be like they are?

Chemical analysis of the glass shows that they are basically sedimentary, basically shaly sandstones. Those in a small area in Europe, particularly, another area in America and one on the Ivory Coast turned out to be associated with a meteorite impact crater. Tektites from a crater in Germany are found in Czechoslovakia, two or three hundred kilometres away. They are the spray from the impact. As the meteorite hits, it explodes like a bomb, and molten sediment or soil or whatever from the crater is sprayed out, almost like water from a hose. The spray then solidifies into droplets which fall down.

The ones in Australia have come from above the equator, from somewhere (not yet located) in Cambodia. They have been thrown up above the atmosphere and then re-entered it at about five kilometres a second. The flanges which developed on them look just like the flanges of a spacecraft re-entering the atmosphere, and actually the same rather flat, saucer shape was used for the design of re-entry modules. There had been a lot of work on tektites, trying to answer how these things could have come in through the atmosphere at high velocity – which was one reason people said they come from the Moon.

There's no contamination from the material of the original meteorite?

There is a very small amount of it present, but so small as to be almost invisible. Because the meteorites are coming at probably 20 kilometres a second, the explosive energy is so high that the amount of contamination is really very low. It is even difficult to find it around obvious meteorite craters. Most of the energy goes into blowing the hole in the ground.

Does the composition of the rock in Cambodia tell you that our tektites originated there?

We know from the isotopic signature giving us the dates, and also because there are various streaks of tektites across Australia. In an area of West Australia the heavy tektites, above about 100 grams or so, lie in a line. Projected back, the lines would meet in Cambodia, or somewhere about the Ho Chi Minh Trail – very awkward places to find. And probably the crater has been filled in with sediment. It's about three-quarters of a million years old, and these craters vanish very quickly. A 90-kilometre crater at the mouth of Chesapeake Bay 34 million years ago produced tektites which finished up in Texas and Georgia, but the crater has totally vanished, filled in – only found by geophysical research.

Would you say the argument is over? Are the non-terrestrial people quiet now?

Well, somebody said that the people had to die off before the argument would subside. One of my friends and I had to write a paper about five years ago pointing out, with reference to another paper which had been published talking about a lunar origin, that the whole thing had been dead for 30 years. It tells you a lot about the human component in science.

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What the 'seven blind men' might think of the continental crust

At about that time you began to work on the growth of the Earth's continental crust. Did you coin the term 'andesite model' for the outcome of that work?

Yes. In the way of these things, I became stuck with the label. Once I got this mass spectrograph running, we could analyse rare earth elements, for example. Then one of my friends – another Oslo person – turned up and said, 'Well, this is a beautiful looking instrument, a lovely toy. What are you going to do with it?' And there's a lot to be said for being given these pieces of advice.

At that point we were worrying about the chains of explosive volcanoes around the Pacific, the famous 'Ring of Fire'. There was again a famous controversy, this time over whether the continental crust had always been here and had just split apart, whether there had been originally a complete cover of granite around the Earth, or whether the thing had grown slowly through geological time. People were adopting absolutely poles-apart positions about continental drift versus unmoving continents.

It's a feature of studying natural history, I think. The problems are so large and so complicated, and the scale on which you have to look at them so big, that you can't easily arrive at the answer and so people divide into camps. The story of the seven Indian blind men examining the elephant – they each find some different part of the elephant – is a very good analogy for a lot of geological problems. As somebody said, what is revealed truth in Cambridge is only a bad joke in Oxford. I got interested in the continental crust for just such reasons.

Rather early in the game, we did some analyses of andesite volcanoes, which are beautiful symmetrical cones like Mount Fujiyama, and are very explosive, like Mount St Helens. They are named from the Andes, and the rock type of which they are made – andesite – is actually very close to the composition of the continental crust. At that time I was working also on the problem of establishing the composition of the crust, because it is very diverse, and this got me into trying to work out a sampling mechanism to look at the crust. One way would have been just to run about, collecting several hundred thousand samples and analysing them all, but there has to be an easier way around these problems.

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Nature's grinding wheel and the andesite model

You have said that the key is in the sedimentary record.

Yes. It became clear that there were lots of sedimentary rocks – muds, shales, sandstones – sitting around because Nature has already done this work for you. It's eroded away the rocks, dumped them in the ocean and mixed them all up along the way, basically just as geochemists used to take rocks in the laboratory, grind them up and analyse them, but on a very large scale. So you can go out and pick up a shale or a sandstone and it is telling you something about where it came from, the history of this large area and so on. Traditionally in geochemistry, people worked on igneous rocks – basalt, lavas, granite, gneiss, relatively simple systems that people could understand. Sediments such as all this mud and sand were thought to be just rather messy and were not worked on very much. It turned out, though, that things like the rare earth elements were astonishingly uniform. You could pick up a shale in Australia, one in Europe and one in America, and they had identical patterns in them.

Nature was doing the sampling for you, providing a mechanism so you could go beyond the detailed sampling to some overall average. You could get a handle on what the crust was made of and then you could say, 'Well, what's making it?' When you looked around, here were these nice volcanoes pushing this stuff up out of the mantle with about the right composition. And this is how the andesite model arose.

So Nature has provided the grinding wheel which you yourself don't then have to use. Is andesite very similar in composition to the sedimentary rocks?

There are similarities, yes. It became apparent that the stuff coming out of the volcanoes is effectively made into the crust, but then you get a lot of melting within the crust itself, usually from the amount of radioactive elements in it and probably also because of lavas coming up underneath it. Then granites tend to form.

To a non-geologist the crust is almost something you can see. What is the thickness of the crust you're talking about?

The continental crust is 40 kilometres thick. The oceanic crust is only five kilometres thick: basaltic lava coming from the mid-ocean ridges, spreading out and diving down at the ocean deep, back into the mantle. Part of that gets remelted on the way, and this is where the andesite comes from. Then that remelts again within the crust. Typically, if you go out and sample the upper crust you come out with granite, which is another stage more evolved than this andesite. But the whole crust together is an andesite composition, fractionated into an upper and lower crust. This andesite model has survived ups and downs over the years, and is actually in fairly good shape.

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The uniqueness of the Earth

Does that model also apply to other planets?

No. This is the interesting thing about the Earth in comparison with the other planetary surfaces. Of the rocky planets, Mercury may be similar (we don't know much about it) but Mars and Venus are typically covered with basaltic lava. Basaltic lavas are what you get in a rocky planet when the mantle starts melting – due to heat from radioactivity, say. In the case of Venus, basaltic lava has covered the planet, and Mars is pretty well covered with it as well. On the Earth, the reason why the lava comes up along the mid-ocean ridges, travels along on this conveyor belt and dives back down into the mantle, getting recycled to produce the continental crust, is probably the water content. Without that we could have been stuck with barren plains of basalt everywhere – no continents, no ore deposits, and so on.

So this mechanism of recycling depends on water content rather than the physical size of the planet. But why would we have more water?

It's one of those chance events. We are just lucky to have it. Mars's very small amount was lost; it has a little bit of water but not enough. Either Venus never had it or it boiled away in an early greenhouse. We don't have very much water, in fact – only about 500 parts per million in the bulk Earth. As somebody says, it's so small we could ignore it to a first approximation except that we're here because of it. It is what makes the Earth unique. The continental crust of the Earth and granite are probably unique in the solar system.

For such a degree of uniqueness to be just chance sounds a bit unlikely. It must be connected, surely, with the size or with the origin of the solar system.

This would perhaps be viable, except that we have Venus as the twin planet – the same size, same density. To a first order, the Earth and Venus are the same planet. And yet they are wildly different, as different as Dr Jekyll and Mr Hyde.

This is proximity to the sun, then, is it?

Slightly, but not really. It's just that Venus has a thick atmosphere of carbon dioxide so it acts as a hot-house. The surface temperature is something like 470º centigrade, and if it had oceans earlier on, the water boiled away. (There may not have been water, of course. That's another argument we have.) I'm not really an atmospherics expert, but probably the primitive atmosphere on the Earth was lost through large collisions, during one of which the Earth melted and the Moon formed.

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Prophetic words

In 1967 you took another period of study leave, this time at the University of California, San Diego. There you met Urey for the second time and he said some prophetic words to you, didn't he?

Yes. It was Harold who had got me interested in tektites. He was a very authoritative person, a homespun philosopher in the great American tradition who loved to give advice to younger people. In his deep voice he used to say, 'I'm just a simple country boy from Indiana, but it seems to me…' He told me, 'Ross, you must always work in important problems' – great advice, if you can identify which problems are important.

Harold was the person who persuaded NASA to go to the Moon. He was a formidable figure. He had a Nobel Prize for discovering deuterium and had worked on the atom bomb during the war as a physical chemist. Afterwards, deciding that he was too far out of touch with physical chemistry, he looked around for something else to work on and discovered the Moon and meteorites. Somebody said he had a love affair with the Moon. He continually talked about it and explained that it was a primitive object: if we went to it we would discover how the solar system was formed. He had sufficient clout to be on all the NASA committees, and using his personality and reputation he persuaded NASA, in effect, that they should mount a mission to the Moon.

The Moon turned out not to be quite what Harold thought it was. That disappointed him greatly, but it did teach us a great deal about the origin of the solar system.

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Preparing for lunar rocks to land in yet another new laboratory

About two years after those prophetic words, you became involved with the lunar missions. How did that come about?

There's lots of serendipity and chance in people's careers. I guess a couple of things came together. Some years previously, Louis Ahrens had asked me to be a co-author on a second edition of his book on spectrographic analysis. I had jumped at such an incredible opportunity for a young person and so I became known as someone who knew about spectrographic analysis. The other thing was my interest in tektites.

On a Christmas card, I think, I told my friend Robin Brett (who had come from Adelaide and was with the US Geological Survey) that I was going to the March 1969 conference on tektites – the one where they took the vote. Robin said, 'I'm now down in Houston, where NASA have taken me on as the chief of the geochemistry branch. We are getting ready for the lunar sample return. Why don't you come and see what we're up to? You can easily come by Houston on your trip.' So I went, and he arranged for me to stay there for about a month.

One day, one of the NASA chiefs called me into his office and talked about the spectrographic laboratory which was being built to receive the lunar samples. I had seen it and talked to the people there, and I knew they were in trouble. Typically of the American system, NASA had subcontracted the running of the laboratory to Brown & Root, a big construction company which had dug some of the Snowy Mountain tunnels – a very efficient company at tunnel digging. They had hired a bunch of technicians to run the spectrograph, but these poor people had no idea how to analyse rocks, because it was a real art. Obviously, Robin Brett had Machiavellian plans when he invited me to Houston, because there I was asked would I run the laboratory for the lunar mission.

So I had to call my wife and tell her about this. She had been expecting me to be home in a month, and we were halfway through building a house. We had just got the walls up when I left. Being a scientist herself, she understood and said, 'Of course you have to stay.' So I settled down with about three months to prepare for the lunar samples, and when I did come home she had finished the house.

What did you have in Houston in the beginning – just the instrument and the building?

Yes. These people had got the instrument operating, but that was all there was. There were no standards. In that business you needed calibration standards very similar to what you were analysing because of various matrix effects. The ideal standard was one which had an identical composition to the sample – and as you deviated from that, you got into increasing trouble. So if you were trying to analyse a limestone using a granite as standard you got wildly erroneous results.

And so you had to have a stab at what the Moon was going to be.

I got together all sorts of standards and things, all the little bits and pieces that make a laboratory run, including some which my very good assistant here sent me from our lab. A lot of these scientific things turn on what appears to be trivia – the sort of mortars you use or the way you mix the samples. We had to mix in internal standards and there were whole problems with mixing procedures, and all the detail. This is what makes the difference, but it is hardly ever written down. I got the lab into shape just as we got the first samples. I was running on about three hours' sleep a night, so it was useful to have developed stamina by growing up on a farm.

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Handling the lunar samples

It must have been very exciting for you, Ross, to see the first lunar samples come in and start work on them.

One of the ironic things when I got to look at the first samples was that the bitter controversy about the origin of tektites added to my fascination to see actually what turned up.

I suppose you had to get information quickly to the press and make sure that what you were telling them was the truth. Doing such precise science under pressure isn't easy.

It was even worse than I expected. We thought we were in fairly good shape for the first samples, which we got in at about noon. It takes only a few minutes to run a sample on the spectrograph; then you have to develop the plates, dry them, look at them on the densitometer, and examine the spectra against wave-length standards and so on to see which lines are present. We did that – and I realised there was something rather fishy with the results. The samples had been extraordinarily difficult to handle. The spectra were very complicated because the samples had about 20 per cent iron, for which the atomic spectra are hundreds of lines. They also had a lot of chromium, a lot of titanium, all these transition elements with lots of atomic spectral lines. We had to fight our way through a real forest of stuff, looking for interferences and so on. And these concentrations were much more than what we were used to looking at in terrestrial rocks.

Are these mass spectra or emission spectra?

These are emission spectra, for which, between about 2,000 and about 10,000 Ångströms, there are 100,000 potential lines. So you needed good dispersion instruments and good knowhow, to see that you weren't being fooled. Clearly something was wrong, and then I realised there was a weak chromium interference on our internal standard line, which was crucial for all of the data. So we had to rapidly find another internal standard line and recalibrate everything. People were hammering at the door, with their hand out for the results, and we were in the midst of this crisis in the lab. You had to know exactly what to do and to do it very quickly.

I'd had by this stage about 15 years' experience in the business, so I realised what the trouble was. You could tell you had an interference. You looked for another chromium line about the same intensity somewhere near, and if that was showing, then you knew you had the interference. The nice thing about spectrographic analyses is that you could be absolutely certain what you were dealing with, and you could say whether elements were present or absent.

Finally, at about 4 o'clock in the afternoon, Robin Brett, who was waiting for the data, ran off and gave it to the press. But even as I was giving it to him, I said, 'No, stop. I don't like the sodium value.' I went back, did a five-minute recalibration and looked at it: 'No, it's not 2½ per cent, it's half a per cent sodium,' which was the right answer. And so the first results appeared in the papers. One's whole professional career was riding on not making any mistake with those samples.

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Quarantine tales

I'd like to read an extract from a speech which was given by John A Wood, who had made the case for your presentation of the Leonard Medal in Dublin in July 1998.

I should say that John Wood is a very distinguished geophysicist, an author of books on the origin of the solar system, a very good friend of mine at that fortuitous time.

He told this story when he was introducing you for the presentation:

'Those were exhilarating times in the Apollo program, and also bizarre times. Samples from the first three missions had to be opened in a sealed glovebox to protect the world from infection by hypothetical lunar microbes. One of the gloves in the box tore while Ross was working near it, theoretically exposing everyone in the room to deadly lunar pathogens. Protocol was that everyone exposed to lunar germs had to be put into quarantine for two weeks.

'However, the quarantine officer on duty was Robin Brett. Robin told Ross he was going to have to sound the spill alarm, but he would delay doing so for a short time so Ross would have a chance to escape the room before the quarantine was imposed. Egress was through the men's room, and as Ross was on his way out through it the quarantine police, suited up in bio-isolation garments, were on their way in. If they encountered Ross, the game was up, but Ross was way ahead of them. As a thoughtful student of military history, he had made a contingency plan to cover a situation like this. He rushed into a small compartment that was near at hand, closed the door, and hid until the quarantine police had stormed past.'

Is that true or false, Ross?

It's reasonably true, although it improves with every telling, particularly by Robin Brett. But I should take the opportunity to assure everybody I didn't put the world at risk due to this exposure to lunar germs.

This was the Apollo 12 mission, three months after the first mission, Apollo 11. There were bizarre features of working under these circumstances, and it was very difficult. Whenever they had spill alarms – sometimes hourly – you had to put on a gas mask until they decided that the alarm was false. (Doing analytical work in a gas mask has to be experienced!) The quarantine officials had masks of very superior quality which were not issued to the ones 'in the trenches'. They had to come by, of course, and tell you what to do, but there was no way they could be heard, so they had to take the mask off to tell you what to do and then put it back on again.

The quarantine had been breached, however, on the initial sample return. When the capsule landed in the ocean, they came with the helicopter, put a flotation ring around the capsule and opened it. They got the astronauts out, took them by helicopter to the deck of the aircraft carrier, and put them in a sealed caravan which was then flown to Houston, because they were worried lest the capsule sink or something. The safety of the astronauts overrode everything else.

The problem was that the lunar dust was extremely dry, so the static charge was very high and the dust stuck to everything – you could take a vial of lunar dust, turn it upside down and it would stay in the vial. The astronauts' clothes were coated with it, the inside of the capsule was coated with it, and as they opened the capsule, the whole Pacific Ocean was exposed to lunar soil. At that point the quarantine already had gone. What we were putting up with was, effectively, a public relations exercise, as was widely understood in the laboratory.

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The geochemical evolution of the Moon

You remained a consultant for NASA for 20 years, didn't you?

Yes, as what they called a principal investigator. NASA were very good about issuing lunar samples. They decided very early that the samples would be available to anybody in the world who was sufficiently qualified and applied to work on them. There were two or three hundred principal investigators at various times working on the samples – the distribution of them is almost a reflection of gross national product. NASA have about 800 lbs of samples from Apollo 11, 12, 14, 15, 16 and 17, and a lot of it even now has not been looked at. About half has been put into storage for future work and so on.

There were lots of different samples, but they fall into two basic types. The dark areas on the Moon which make the pictures of the Man in the Moon are lava flows on the surface, mostly filling hollows excavated by large impacts. The white areas are basically a very thick crust, anywhere between 60 and 100 kilometres thick and mostly of feldspar, which is a very unusual composition. This answered another puzzle about the Moon, because on terrestrial analogues people thought these white areas were probably something like granite. We learned that terrestrial analogues were very dangerous: everything in the Moon is a bit different.

I think much of your work on the evolution of the Moon after its creation arose from your study leave at Houston in 1973-74.

Yes. The chemistry of the samples was very complicated. They had lots of strange features relative to terrestrial chemistry: in the lavas there was lots more iron, chromium, titanium and so on, and the highland (white-crust) samples, were mostly feldspar, but in the crust there were also very high concentrations of elements such as thorium and uranium. All this was a great puzzle, because nothing fitted anybody's previous ideas about how the Moon had been formed. Certainly it wasn't a primitive object; it was obviously a very fractionated object, unlike what Harold Urey had wanted. So everyone was busy analysing, and producing endless amounts of data – we had thousands of pages of papers dealing with analytical details of the Moon, but no broad overview. The director of the Lunar and Planetary Institute at Houston asked me to try to make some sense of it all, and so I sat down at Houston for a year and tried to work out exactly what all this stuff meant: how the Moon had come to have a thick crust of feldspar, how these lava flows had come into existence and so on. And I produced a model of its geochemical evolution.

We soon realised you had to start with a completely molten Moon, which was a very strange, worrying thing – how did you melt it? Then, having melted it, you went through a crystallisation sequence: you started forming minerals like olivine, which sank to the bottom, and feldspar, which floated to the top. And you did a gigantic differentiation of a fractionation moon, so you finished up with a crust like icebergs of feldspar, floating on a liquid which then slowly crystallised underneath. From that, subsequently, a little bit of radioactive heating in it produced lava which came out and flooded over the top of the white crust, producing the dark markings on the Moon. That's pretty much the standard model now, but like all these things it survives intense amounts of criticism – from some of my nearest colleagues, actually.

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An answer to how the Moon arose

If that model depends on an initial molten state for the Moon, what is your theory of its origin?

This was a great puzzle. We continued working for another 10 years or so on the details and examining this model of evolution. To this day people still produce large amounts of data from the lunar samples, but by 1984 people began to say, 'This is all very well, but how did the Moon arise? Now you know what it's made of and what happened to it, what's it doing there?' The Moon is unique in the inner solar system. Mars has two tiny moons, Mercury doesn't have one at all, Venus doesn't have one. What is the Moon doing there, how did it get there and why is it different in density from the Earth? (It is about half the density of the Earth.) This is a classical problem known from at least the 19th century: how do you get two bodies close together differing in density by a factor of two? Everyone had a model to make, but none of these models worked and survived the funny chemistry we began to find.

Did the fact that the chemistry was so different trigger the unseating of some of the earlier models?

That was one of the triggers. Another was supplied by Al Cameron, a nuclear physicist who had come up with a model for the nuclear synthesis, the elements, at the same time as Burbidge, Burbidge, Fowler and Hoyle had produced their papers. Cameron worked it out when he was in Canada with the Atomic Energy Commission, and he possibly should have had a Nobel Prize as well as Willy Fowler. He said that because the Earth–Moon system is spinning very rapidly, you have to hit it with something very big, the size of Mars, to produce the angle of momentum of the system. Because there were so many ideas floating around, we thought we'd better have a conference – as you do when you have an insoluble problem.

The next question was where the conference should be held. An old version of the origin of the Moon is that it came out of the Pacific Ocean. In fact, a paper in Nature in 1881 said that it is perfectly obvious: there's a big hole where the Pacific Ocean is and there's a ring of volcanoes around it where the Earth is still trying to 'heal' itself from this event, so somehow the Moon spun out of there. We thought if we had a conference in Hawaii, in the middle of the Pacific Ocean, we might get some special insight. And it certainly worked – Cameron's model became the only model in town. His idea took a lot of swallowing, but then it produced desirable effects. It melted the Earth and it produced your molten Moon.

Was it fully molten?

Yes. There still were some arguments because some people would like it half-molten, but it's almost certainly been fully molten. It has even been fairly well established now that there is a tiny iron core in the Moon – not very big, about three or four per cent of the Moon. So in Cameron's model you hit the Earth with something the size of Mars, at a glancing angle, and what spins out into orbit is not bits from the Earth but bits from most of the impactor. (Some of it falls back on the Earth.) The iron core of this body, however, rams back into the Earth. You're left with a ring of silicate debris out in orbit, from which the Moon is collected and forms rather quickly. This explains how you get a Moon which is essentially rock, low density, sitting along with the Earth, which has a large iron core and a high density.

All this gathers, under gravity, in less than a day, while everything is still at very high temperature – which explains why the Moon is bone-dry. We can't find a trace of water on the Moon at all. And it explains another strange thing about its chemistry: it is depleted not only in water but also in elements like lead, thallium, bismuth, which are volatile at about 1,000º centigrade. These too have gone, leaving the Moon composed of rather refractory materials.

All the rest just boiled away?

Yes. So you need a high-temperature event, which Cameron supplied with his model, but the dynamical problems are still being argued about.

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Having a go at the solar system

Back in Australia you continued to work on the continental crust, and about five years before you retired you decided to extend your work to the evolution of the other planets. What set you on this new tack?

Well, as one gets close to retirement the options are to continue working as you did when you were post-doc, or to take some broader view of things, to try to arrive at some overall answer – although that is a well-known trap and one has to be careful in these matters. I wrote to the director of the Lunar and Planetary Institute in Houston, suggesting that I come there again on sabbatical and work on another book, using their very good facilities for producing books. He said, 'Yes, you can certainly come here and do that, but you're not allowed to write another book about the Moon.' In order, then, to do something a bit different, I thought somewhat brashly that I would have a go at the solar system. By this time we had a lot more data from the Pioneer and Voyager missions to the outer planets – a vast amount of data not only from the Moon but from Jupiter, Saturn, Uranus, Neptune and the satellites and so on. I started to try to put all this together, and found that the solar system seemed to be a very untidy place. For example, although the planets were more or less in circular orbits, they all rotated at different speeds, they were tilted at different angles, none of the satellites looked like one another.

I came to the view that chance events in the shape of large impacts and so on during the formation of the system had been the dominating influence. Chance became the theme of the book, eventually – that the solar system was not something you produced by sitting down with a large enough computer and putting all the physics and chemistry constants into it, but rather there were very many chance events intervening. You had random events, like the origin of the Moon, which were unpredictable, and such strange things as Venus rotating very slowly backwards (it takes 243 days for one rotation), and Uranus lying on its side, with its rings of satellites in equatorial orbit around it. And, later on, new planets were discovered which didn't bear any resemblance to our present system.

My view was quite well received, and a number of astronomers told me that they liked the book. I was very pleased to hear this, because stepping out into areas where one has very little expertise could be quite dangerous.

You have a lot of expertise, I would say. I think you now have seven books altogether, in addition to 225 or more papers.

Yes. This is one of the advantages of working at the Australian National University at the time I was there, when one was hired to do research. I always took this rather seriously. Having been in teaching departments, and seeing the problems that my friends have in other universities – with students and most of the time taken up with other matters – I recognised this as a wonderful opportunity to work.

The first book was on spectrochemical analysis, with Louis Ahrens. Then I wrote a small one, just after the Apollo missions, and one at Houston in 1975, explaining my model for lunar evolution. I did another edition of that and then I worked with one of my students to write a book on the continental crust – its chemistry and the chemistry of the sediments. That book is constantly referred to. (I have learned that you must put lots of data into books if you want people to refer to them.)

Then I wrote a book on the solar system and I am now working on its second edition. A couple of years ago I wrote a more popular book called Destiny or Chance, which was about whether the solar system arose by a series of chance events or was a pre-ordained thing you could just pull out of some computer program. Unfortunately, perhaps, the more I think about that, the larger the number of chance events I think there have been.

On your retirement there was the Taylor Colloquium on the differences and similarities between the planets of the solar system.

Yes, and also on planetary crusts, the continental crust and so on. I have kept one foot on the Earth and one on the Moon!

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Matters of honour

In recognition of your contributions to geochemistry and geology you have been given a number of prizes and awards, including the Goldschmidt Medal of the Geochemical Society of America and, in 1988, the Leonard Medal of the Meteoritical Society. Whether John Wood is your friend or foe I'm not sure, in view of the two stories he told in the citation for that award. The second of those related to a keynote talk you were asked to give at a plenary session of one of the earliest lunar science conferences. Wood told in agonising detail how Robin Brett, expecting you to be easily flustered when you spoke, arranged for you to be tricked into thinking an attractive young woman was about to climb onto the stage and, as you were beginning to talk, unbutton her trenchcoat and 'flash' you.

As Wood put it, 'What would Ross do? We don't give Leonard Medals to people who couldn't handle such a situation. Ross just said, "First slide, please," and the room was plunged into darkness.'

That's a true story. I thought there had to be some way to handle this problem.

In addition to being a Fellow of this Academy, you are an Honorary Fellow of the Royal Society of New Zealand and – perhaps the greatest honour of all – in 1994 you were elected as a Foreign Associate of the US National Academy of Sciences. That is a high honour, not given to many Australians.

About 15, I think. It came totally out of the blue. I was really astounded by it.

Another honour came your way in 1997, when an asteroid was named after you: 5670 Rosstaylor. The citation says it is equal to 1985 VF2. What do all those names for one asteroid mean?

The asteroids are numbered in sequence of discovery, No. 1 being Ceres, discovered in 1801. About 12,000 have now been discovered. They are assigned a number when the orbital elements are sufficiently well established so that the asteroid can be recovered. The man who found Ceres lost it again, and it was recovered by Olbers, who was famous for his paradox: why is the sky dark at night? This asteroid is No. 5670 in sequence of discovery, and it was picked up in 1985 by Gene Shoemaker. It is about 30 kilometres in diameter. The shape is not too clear at the moment, but Gene Shoemaker said its surface area is big enough for a decent sized New South Wales sheep station, if only you could get the sheep there. It is sitting at about three astronomical units from the Earth in a moderately eccentric orbit – which I find slightly amusing.

Gene Shoemaker and his wife were asteroid and cometary discoverers. Gene was a geologist, responsible basically for establishing the meteoritic origin of large-impact craters on the Earth. (There were very large arguments about that when I was a student.) By about 1960 Gene had decided that the big crater in Arizona, for example, was formed by an impact of a meteorite and not some kind of internal explosion of the Earth. He then established the principles for geological mapping of the Moon and so on. Tragically, though, only a couple of months after this he was killed in a car accident out in West Australia, where he was looking at meteorite craters – for the past dozen years or so, with his wife, he had done a lot of mapping in the outback in Australia, amongst a host of other activities. His loss was irreparable.

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The extreme age and fascination of meteorites

You have also an interest in meteorites, I believe.

Yes. At one point I was President of the Meteoritical Society. Meteorites, which come from the asteroid belt, are of great interest as the oldest objects we can get our hands on in the solar system. Mostly, meteorites are broken-off bits of asteroids, and a number of them have iron cores. I have with me one which is a mixture of an iron core and rocky, olivine crystals from the mantle of a small body which had formed like a very small-scale analogue to the Earth. These date right back to the beginning of the solar system, having formed within, probably, three or four million years of the beginning of the solar system. So the great fascination of meteorites is their extreme age. They tell us about events. There's a great gap on the Earth of another 500 or so million years before we find any rocks at all. We find rocks on the Moon filling that gap back to within perhaps 100 million years of the formation of the system, which makes the Moon very useful.

That piece has really large pieces of iron right throughout it.

Some of the iron meteorites are extremely massive pieces, and what's nice about this one is that it has the mixture with the olivine crystals. These are probably the most spectacular meteorites. When a meteorite hits, explodes and blows the crater, its main mass vaporises. But bits are blown off the meteorite or bits come off it as it comes through the atmosphere, and so there are usually lots of bits of meteorite scattered around the craters. This piece is from a small crater, probably less than the size of this building, in the middle of Kansas.

Ross, you've had a very prolific and extremely interesting career. Thank you very much for sharing some of it with us.

Well, it's interesting to think of the areas you find yourself working on. Just being led from one area into the next, just following your nose, you can finish up in the middle of the solar system.

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