Toxic algal blooms – a sign of rivers under stress
Box 2 | Cyanobacteria: the simple things of life
Cyanobacteria, also known as blue-green algae, started out on Earth quite a while ago. Their fossils have been found in rocks that are about 2500 million years old.
They are with us still. Indeed, blue-green algal blooms are becoming increasingly more evident in Australia's rivers and lakes as human activities create conditions in which they thrive.
Bacteria are characterised by prokaryotic cells
Cyanobacteria are 'prokaryotic' life forms, which simply means that the genetic material in their cells is not enclosed by a membrane. This characteristic is distinctive of bacterial cells; all other cells (eukaryotic) have their genetic material contained inside a membrane.
Bacteria are hardy creatures
Bacteria can survive in hot, cold, salty, acidic and alkaline environments in which eukaryotes would perish. They have a bad image: after all, they cause many diseases in humans, some of them fatal.
Yet, without them we might not be here. Most scientists believe that the earliest life forms were bacteria, simple creatures that fed on carbon compounds that were accumulating in Earth's early oceans. In the harsh conditions that were present then, no other organism could have survived.
Other organisms evolved from early bacteria
Slowly, other bacteria evolved that could use the sun's energy to manufacture their own food. Cyanobacteria then went a step further: they started to extract hydrogen from water during photosynthesis, releasing oxygen as a by-product. Over time, enough oxygen accumulated in the Earth's atmosphere to allow the evolution of oxygen-using organisms.
We could even owe them more than that. Many scientists think that eukaryotic cells may have evolved from prokaryotic cells which 'swallowed' other prokaroytic cells, thus creating membrane-enclosed nuclei.
Regardless of how it happened, the creation of eukaryotic cells was a significant milestone in the history of life on Earth. As conditions became more favourable, there was a rapid expansion in biological diversity and the evolution of ever more complex organisms.
Two or three billion years later, we have reached a point in our own evolution where we can peer down a microscope at perhaps a thousand of these tiny life forms drifting about in a drop of water. Are we looking at our ancestors?
Boxes
Box 1. Is Newcastle's water vulnerable to toxic algal blooms?
Box 3. Harmful effects of blue-green algae on human health
Related site
Cyanobacteria: Fossil record
Posted August 1997.