CREATION - Snowball Earth - page 98

early worm. 13 But most of his colleagues sigh and point out that there's no sign of the creatures them-
selves among the “trails”, which makes his argument much harder to swallow. Other researchers have
just reported the discovery of blobby grooves, like worm casts, in 1.2-billion-year-old sandstones from
southwestern Australia. 14 But once again, there's no sign of any animal, nor any clear evidence that
complex creatures really created these “trails”, and few biologists think they pose problems for the
Snowball theory.
More troubling, though, are the algae. Algae are marine plants that live throughout the modern
ocean. Some are small, hairy blobs floating through the water or clinging to rocks. Others are huge.
Kelp is a form of algae, and the kelp forests off the coast of California contain plants that are hun-
dreds of feet tall. Algae certainly existed before the Snowball. There was nothing like kelp; the biggest
creatures were just a fraction of an inch across. But they were almost certainly multicellular.
For instance, Nick Butterfield, a Canadian biologist now at Cambridge University, has found fab-
ulously preserved red algae in a lump of chert that he collected from Somerset Island in the Canadian
Arctic. The rock is 1,200 million years old, and the fossils it contains are tiny, hairy things, scarcely
visible to the naked eye. But when Nick put his samples under a microscope, he realized that the fossil
images were dead ringers for a modern red alga called Bangia , which you can scrape off rocks on
many seashores today. He saw the classic rows of disc-shaped cells that make up the Bangia 's fila-
ments, and the wedge-shaped cells that adult Bangia possess, having divided their discs into eight,
twelve and sixteen pieces. He also saw separate cells that were orientated vertically, and appeared to
be making up a “holdfast”, a kind of anchor that could bind the alga into the seafloor and enable it to
grow upwards rather than merely sideways like the primitive flat mats of Slimeworld. 15
Then there's fancy filamentous algae from Spitzbergen, which look much like green algae does
today. And a strange beast named Valkyria , with appendages that look almost like legs (but aren't).
And a Siberian fossil found by Andy Knoll, a colleague of Paul Hoffman's at Harvard, which looks
just like a modern green alga called Voucharia . Many of these are not just collections of cells. They
really look as if they've already learned to specialize.
These finds may seem to topple the biological part of the Snowball argument, but they leave open
one big mystery. Algae apparently learned to be multicellular by 1.2 billion years ago. If they then
passed on the secret to the rest of the world, why did it take another 600 million years before animals
did the same? If this was the crucial step that changed the world for ever, why did the rest of the planet
stay mired in simple slime for so long afterwards? Nobody believes that one evolutionary event can
trigger another occurring hundreds of millions of years later. Even Nick Butterfield says so. “There's
still this huge delay before things got rolling,” he acknowledges, rather sadly. “Biology moves faster
than that.”
There are, then, two remaining possibilities. Either algae invented complexity separately, and kept
the secret to themselves— which would pose no particular problem for the Snowball idea—or there
were plenty of complex animals around before the Snowballs, but they left no trace in the rocks. That
would definitely be a problem, since the Snowball couldn't trigger something that already existed long
before. But how would you test this without fossils? There might just be a way. The evidence would
come not in the form of fossils, but from applications of a more oblique approach known as a “mo-
lecular clock”.
The genetic material—the molecule called DNA—inside every living cell contains information
about its ancestry. In principle, with a sample of my DNA and some of yours, we could work out how
closely you and I are related. Although we are both humans, your DNA differs slightly from mine.
That's why our faces are perhaps different shapes, or our eyes a different colour. These changes in