Geology Reference
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of methane gas into the atmosphere. This methane adds significantly to the greenhouse ef-
fect, which causes the oceans to warm even more. Some scientists now point to a possible
catastrophic Neoproterozoic release of ocean-floor methane as a way to accelerate global
warming, perhaps flipping Earth from cold to hot in a matter of decades.
This Neoproterozoic scenario depends strongly on the sources of methane. If microbes
produce most of the ocean's natural gas, then clathrate production probably slowed during
snowballepisodes,andmethanereleasemaynothaveplayedsuchamajorroleinwarming.
If,ontheotherhand,asignificantamountofmethanerisesfromthehotpressurizedmantle,
then stores of methane clathrates would have built up continuously throughout any global
cooling spell independent of microbial life, triggering a much greater feedback. So what
process produces the methane—deep rocks, shallow microbes, or a combination of the
two?
The question of deep versus shallow origins of methane may seem straightforward, but
it's a problem colored by a long-standing, sometimes heated international controversy in
the oil and gas business. Petroleum is formed primarily of hydrocarbon molecules, of
which methane is the simplest and most abundant. It's widely assumed that whatever nat-
ural processes form methane also play a role in the formation of oil.
OnonesideofthedebateistheRussian-Ukrainianschool,fatheredinthemid-nineteenth
century by the famed Russian chemist Dimitri Mendeleev, best known for his ubiquitous
periodic table oftheelements. Mendeleev proposedanabiogenic originforpetroleum long
beforetherewereexperimentstobolsterhisclaims.“Thecapitalfacttonote,”hewrote,“is
thatpetroleumwasborninthedepthsoftheEarth,anditisonlytherethatwemustseekits
origin.” Mendeleev's ideas enjoyed resurgence in Russia and Ukraine in the second half of
the twentieth century, and they inform Russia's thriving oil and natural gas industry. Some
Russiangeochemistsstilladvocatethatvirtuallyallpetroleumandnaturalgasderivesfrom
deep abiogenic sources. In their view, some productive oil fields are renewable resources,
continuously filling from vast mantle reservoirs below.
Such thinking is scientific heresy to most American petroleum geologists, who cite a
litany of evidence for an exclusively biological origin for petroleum: oil is only found in
sedimentary horizons where life once thrived; oil is loaded with distinctive molecular bio-
markers; the isotopic composition of oil is uniquely lifelike; the trace elements also point
to a living source. For many North American petroleum geologists, the case is settled: vir-
tually all petroleum and natural gas is biogenic.
The debate, polarized by decades of Russian-American rivalry, was rekindled in North
America by the brilliant, pugnacious, far-reaching Austrian astrophysicist Thomas
(Tommy)Gold,whotaughtatCornellUniversitybeforehisuntimelydeathin2004.Gold's
chief claim to scientific fame, at least within his chosen specialty of astrophysics, was his
realization that metronomic radio pulses from deep space, the so-called pulsars, are in fact
