SNOWBRAWLS - Snowball Earth - page 79

have taken place there. The idea is that a sudden underwater landslide could reduce the pressure on
the hydrate deposit, decomposing it and sending deadly bubbles of gas up to the surface. This is plaus-
ible enough geologically, but, sadly, the shipping end doesn't hold up. The Bermuda Triangle simply
hasn't swallowed an abnormal number of ships—ask Lloyds of London.
Still, methane hydrates have apparently been responsible for real-life dramas in the past. In the
Barents Sea, just off Norway's northeastern tip, hydrate deposits seem to have exploded thousands of
years ago, leaving behind giant craters that pockmark the seafloor. That probably happened at the end
of the last ice age, when warmer seas destabilized the hydrates there until they erupted like a volcano.
And some researchers believe that destabilized hydrates released more than a million cubic kilometres
of methane at the end of the Palaeocene, about 55 million years ago.
Martin Kennedy wants to explain the carbonates that blanketed the Earth immediately after the
Snowball in the same way. Methane hydrates, he thinks, might have been more widespread than they
are today. After all, everyone agrees that conditions were colder then. When warmer temperatures re-
turned, those methane hydrates would have released their gas, to be quickly oxidized and precipitated
into the ocean as a blanket of carbonate. 3
Martin felt that he had found clear evidence for this idea in the Noonday dolomite in Death Valley.
That's why he was so excited. The chevrons filled with cement, the rocks that looked as if they had
been simultaneously squeezed and stretched, the “worm burrow” structures—all of these could have
been caused by decomposing methane hydrates. As the light methane travelled upwards through the
heavier mud, it would have created tube-like vertical passageways, just like the dark tubes in the rocks.
And if the gas hit an obstruction—a microbial mat, say, which is dense and rubbery—it would have
lifted the mat up into a dome, creating both the chevron shape and the cavity that cement would even-
tually move in to fill. The strange structures in the Noonday dolomite were Martin's missing evidence.
“They're stunning,” he breathed. “They do exactly what you'd predict. It's better than I could ever
have imagined.”
Martin wasn't just trying to disprove Paul and Dan. He had other reasons for preferring his ex-
planation of the cap carbonates. Martin, like Nick, is deeply rooted in the world around him. He too
thinks that seeing is believing. And he likes his methane theory precisely because it uses processes
that we see happening today. There's plenty of methane hydrate in the world right now. This explan-
ation for the caps doesn't require insanely high weathering rates, an extreme hothouse after the ice, a
frozen ocean, all the things that make Paul and Dan's Snowball so radically different. “Paul and Dan's
Snowball is really non-uniformitarian,” Martin told me once. “It really worries me when you suddenly
evoke a Martian-like world.”
But there are some things that Martin is willing to admit, and that Paul and Dan immediately seized
on. His methane idea doesn't explain nearly as much as Paul and Dan's theory can. It can't explain
the iron formations or the ubiquitous ice. It tells you nothing about why the Snowball might ulti-
mately have ended. And it doesn't necessarily oppose Dan's explanation for the cap carbonates. Even
if Martin was right, the hydrates could have been decomposing at the same time that acid rain was
lashing on to ground-up rocks. There's nothing to stop the two effects working in tandem. Martin's
methane-hydrate theory, it turns out, doesn't disprove the Snowball at all.
Martin, however, had another challenge to make. All of Paul's information about the Snowball
ocean came from the isotopes in his carbonate rocks, but he only had carbonates from before and after.
Martin, on the other hand, had found something extraordinary. He had carbonates from during the
Snowball. And they seemed to show that Paul's Snowball theory had a fatal flaw.