Geoscience Reference
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It's a slow process. Stromatolites grow just a fraction of an inch each year. The ones in Hamelin
Pool are hundreds of years old and would be astonishing feats of engineering, had they been created
by design. For these micro-organisms to erect a stromatolite three feet high is like humans building
something that reaches hundreds of miles into the sky, and scrapes the edges of space. I wade a hun-
dred yards, two hundred yards offshore, and the slope is still so gentle that the deepening is barely
perceptible. Mercifully, the flies and butterflies have dropped back, and the birdsong is out of earshot.
At last I begin to feel that I've travelled back to life's earliest days.
H AMELIN P OOL'S mats and stromatolites look utterly alien, but they were once ubiquitous. Time was,
this scene of stromatolites and stippled microbial mats would have greeted you everywhere you went.
Forget dolphins and wallabies. This is how the Earth looked for nearly three and a half billion years.
The imprints of the stromatolites and their mats show up still wherever sufficiently ancient rocks poke
through to the Earth's surface. I've seen them in Namibia, in South Africa, in Australia and California.
They are sometimes dome-shaped like these in Shark Bay, sometimes cones, sometimes branching like
corals. There are places where you can walk among ancient petrified stromatolite reefs, rest your feet
on their stone cabbage heads, and see where they have been sliced through to reveal rings of petrified
growth. And you can run your fingers over fossilized mats, which give rock surfaces the unexpected
texture of elephant skin. This slime used to be everywhere, and now it's almost nowhere.
How did we get from there to here? This is at once a simpler and more powerful question than it
seems. Of course, life took many separate evolutionary steps on its way from stromatolites to walla-
bies. It had to invent eyes and legs and fur and feet, and everything else that distinguishes marsupials
from slime. But there was one particular step that was more important than all the others, one that
made all the difference.
The step was this: learning to make an organism not from just one cell, but from many. Though the
first microbes on Earth were woefully unsophisticated, they did gradually learn new tricks to exploit
the planet's many niches. But they all still had one thing in common. Each individual creature was
packaged in its own tiny sac, a single microscopic cell. Then at some particular point in Earth's his-
tory, everything changed. One cell split into two, then four. From that time onwards, organisms could
be cooperative, and above all their cells could specialize. There could be eye cells and skin cells, cells
to make up organs and tissues and limbs.
For life, this was the industrial revolution. Forget the old cottage industries. Now you could have
factories with production lines. Parcelling out tasks and specializing is always more efficient than try-
ing to do everything yourself. And there are some things, wallabies for instance, that can only be made
with a massive collaborative effort.
In just the same way, when organisms developed the ability to become multicellular, they gained
a world of possibilities. Your body is made up of trillions of cells. Every hair is packed with them.
You shed skin cells whenever you move. Your blood cells carry energy around your body, to feed the
organs made up of still more cells. This multiple identity is the one criterion that's vital for any com-
plex creation. Every dolphin and dugong, every shark, pelican and wombat depends for its existence
on that crucial leap from one cell to many. This was the point when simple slime yielded its pre-emin-
ence to the complex creations that heaved their way out of the sludge and started their march towards
modernity.
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