Bugs and breakfast

If you look at a map of Australia, the big lump in the top left corner is the Pilbara region. Here all is red, green and blue - the red of the rocks, the green of the prickly spinifex grass, and the blue of the sky. In some of these red rocks we find the oldest fossils in the world. But they are not fossils of bones or shells. Amazingly, they're fossilised stromatolites, a bit like the ones still growing today in other parts of Western Australia.

In the 1980s, scientists collected some dark grey, flinty rocks that are found with the fossil stromatolites. They cut the rocks with a special diamond saw, into really thin slices, thinner than tissue paper - slices so thin you can see through them. Then, using a very powerful microscope, the scientists were able to find the actual fossilised remains of the bugs that made the stromatolites.

We owe a lot to these bugs, particularly the cyanobacteria. Incredible as it may seem, they gave us the oxygen we breathe. Even more surprisingly,

they made the mountains of iron ore in the Pilbara. These are mined and turned into the cans which contain the baked beans you had for breakfast and the car that you were driven to school in.

Speaking of baked beans . . . Before there was oxygen in the air, a few thousand million years ago, there was a lot of methane. (That's the unmentionable gas that appears when you've eaten too many baked beans.) There was also a lot of another gas, carbon dioxide. Like plants today, the ancient blue-green bugs turned the carbon dioxide into sugars, using energy from sunlight. A side product was the gas oxygen. When these bugs first started doing this, oxygen bubbled into the sea. This caused iron minerals dissolved in the sea to turn into rust.

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For hundreds of millons of years the sea continued to produce rust. These iron-rich muds have since turned into the great mountains of iron ore that today are mined in the Pilbara, to make your baked bean can, your parent's car, and so on.

The little bugs kept on soaking up the carbon dioxide and spitting out the oxygen. Once the air became rich in breathable oxygen (probably about your shoulder on our trip down your arm), some of these simple bacterial cells came together, some living inside others. And so evolved slime and the first seaweeds (near your elbow). Some time after that, though we don't know exactly when, other cells got

First seaweeds appear

First seaweeds appear

('Evolved' means 'changed over a very long period of time' - see pages 12-13.) We are still hunting for their fossilised remains. Maybe they are so tiny that we won't be able to find them.

So, we owe a lot to those early slimy bugs. Not only did they give us the air we breathe and our tin cans, but they're also our extremely long-, long-, long-lost ancestors. In between us and them are some fearsome and far-fetched creatures, as you'll see when you read on.

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