EUREKA - Snowball Earth - page 53

stuff about the Snowball is fascinating! You can't bury it! You can't just put one little sentence in about
the implications. You need to think about this idea more. What does it mean ?
Paul didn't need a second invitation. He had been hoping Dan would bend his brain to the Snow-
ball story. So Paul told Dan about the strange cap-carbonate rocks and about how unexpectedly light
the carbon isotopes were. He told him about the weird textures: the huge, graceful crystal fans, and the
wormlike tubes.
He also told him the whole story as it stood then. That the Earth had frozen over, top to toe, pole to
pole. That during this Snowball, volcanoes had continued to spew their greenhouse gases over the fri-
gid Earth. That over millions of years the planet's atmosphere had become scorching. That this super-
greenhouse catastrophically melted the ice. That the greenhouse gases stayed around afterwards for
tens of thousands of years, blasting the Earth into a hothouse until they finally subsided.
Dan listened carefully. He retreated into a corner to think, while Paul and the friend politely chat-
ted. When Dan is concentrating on a problem, he goes silent. His eyes dart around, focusing on
something out of view. He often bites his bottom lip. Then, when he comes upon an answer, his eyes
fire up. He immediately, eagerly, blurts it out. Wait! I've got it! I can explain the carbonates!
His idea was brilliant.
The planet was in stasis, cryogenically preserved. A thick layer of ice covered the oceans. Great
glaciers crept and ground their way over the rocky surface of the continents, slowly pulverizing
everything in their path. Ice bred more ice as the shining white surface repulsed sunlight, locking Earth
in the mother of all winters.
So it was, and so it would always have been, but for volcanoes that poked above the ice or
squatted on the seafloor. They erupted, as they always have, and each eruption spewed out ash and lava
and—above all—carbon dioxide gas. Gradually, slowly, this volcanic gas built up in the air, wrapping
the Earth in a blanket of warmth. And in the end, fire conquered ice. Drip, drip, came the first sounds
of change, then trickle, then flow, then flood. Then meltdown. The ice vanished, and Earth went from
icehouse to hot-house in a geological instant. So much was Joe Kirschvink's vision.
But now comes the new part, the part that suddenly dawned on Dan one Sunday night in Harvard.
That hothouse, he realized, was like the tropical heat engine gone mad. The ice had gone, but the heat
that melted it remained behind, on full blast. Dry, scorched air sucked up moisture from the oceans and
whirled it into storm clouds. Hyper-hurricanes raced around the Earth's surface, flinging their watery
burden back on the ground in torrents. And that burden was no longer just water. The air was filled
with carbon dioxide. Whatever rain passed through it turned immediately to acid.
What did the acid rain fall on? An inviting layer of powder. Over millions of years, glaciers had
ground the continents' rocks into dust. Ground-up material is always easier to react with. Think how
much faster sugar dissolves when it's not bound up in a lump. In the post-Snowball world, that com-
bination of ground-up rock and torrential acid rain was a chemical factory waiting to happen. Rock
dust and acid met, mated and were swept off into the sea. They set the waters fizzing and foaming,
creating a Coca-Cola ocean.
And then a new snowstorm began, this time underwater. All around the world, the post-Snowball
ocean turned milky with flakes of white. They poured down on to every inch of the ocean floor. From
the chemistry of acid rain and rock dust had come a massive outpouring of carbonate, which blanketed
the entire planet. The flakes squeezed together, and hardened and turned into rock. They were the cap
carbonates. This was Dan's idea. The cap carbonates, he said, arose directly from the intense, bizarre
conditions that had rescued the Earth from its Snowball.