Geoscience Reference
In-Depth Information
damning review with one of his favorite quotes: “False facts are highly injurious to the progress of
science for they often endure long: but false views, if supported by some evidence, do little harm, for
everyone takes a salutary pleasure in proving their falseness.”
This comes from Charles Darwin, the originator of the theory of evolution, and it makes an import-
ant point. When people argue about ideas—“views”, in Darwin's words—all the arguments have to be
based on the available “facts”. If one of the facts is wrong, the whole edifice can crumble—taking
all
the ideas with it.
But whose “facts” were wrong—Paul's or Martin's? Had the rocks come from the Snowball ocean
or not? Paul might be right about the “picket fence” crystals from Namibia and their related cements. It
is possible that the crack they grew in was from some earlier time, and that the whole lump of rock had
then broken off and been amalgamated into the younger Snowball formation. In the end, Martin left
those samples out of his paper, just in case. But the peloids are harder to argue away, and the caviar-
like oolites harder still. To break those off from older rock and transport them and mix them into a new
formation would surely have smashed their delicate structures. They really did seem to come directly
from the Snowball ocean, just as Martin said.
So was this indeed a fatal flaw in the Snowball argument? After all, the carbonates leading up to
the Snowball had been light, and Paul had assumed that the ones that formed during the Snowball
would be the same. But he hadn't made any direct assertions about this in his papers. Unlike Martin,
Paul had no carbonate rocks from the Snowball period; with no data to interpret, neither he nor Dan
had thought particularly hard about what the isotopes would be like. Now, though, they had an incent-
ive. Spurred on by Martin's findings, Paul and Dan focused on this issue. And for two different though
complementary reasons, they realized that you'd actually
expect
the Snowball ocean to be heavy—just
as Martin had found. Ironically, Martin's heavy rocks didn't conflict with Paul and Dan's model at all.
Paul had realized that the oceans would have been heavy because they contained old material, dis-
solved from rocks on the seafloor. The floor of the Snowball ocean was lined with carbonate rocks
that had been created when life was still abundant. And the acidic seawater would have dissolved this
old carbonate, just as acidic lime juice can dissolve a marble cutting board. The effect, says Paul, was
to change the signature of the ocean. If you pour hot milk onto cocoa powder, the milk turns brown
because the dissolved cocoa swamps the milk's original colour. Similarly, the “heavy” signals of plen-
tiful life dissolved from the old seafloor carbonate would have swamped the “light” signal from the
largely lifeless Snowball ocean.
Dan has discovered another effect that reinforces this one. His answer involves a more arcane is-
sue, beloved of geochemists and understood by few others. The carbon isotopes in the ocean don't
depend only on the activity of living things; they are also affected by the way carbon dioxide gas mi-
grates from the atmosphere into the ocean. And this in turn depends on what proportion of carbon the
atmosphere already contains.
Nowadays the atmosphere has only a tiny proportion of carbon, less than 5 per cent. But the Snow-
ball was very different. According to Paul and Dan's model, carbon dioxide gas had been building up
in the atmosphere for millions of years. The Snowball atmosphere contained a much higher proportion
of carbon, and that would have made all the difference.
Dan did the sums. He crunched through all the equations that predict how this change would affect
the ocean isotopes. And he came up with a number that matched—precisely—the heavy values Martin
had found. Even if the Snowball ocean was totally lifeless, the carbonate cements would be just as
firmed
the Snowball theory.
