My Mind and Matter column in the Wall Street
Journal is on abiogenic methane
Coal, oil and gas are “fossil” fuels, right? They are derived
from ancient life-forms and are nonrenewable, stored energy,
extracted from prehistoric sunlight. In the case of coal and most
oil, this is obviously true: You can find fossil tree trunks and
leaves in coal seams and chemicals in oil that come from
plankton.
But there’s increasing doubt about whether all
natural gas (which is 90% methane) comes from fermented fossil
microbes. Some of it may be made by chemical processes deep within
the earth. If so, the implications could be profound for the
climate and energy debates.
When the Earth was forming, the meteorites that crashed into its
surface were about 3% carbon by weight. Some carbon was in the form
of simple hydrocarbons. Gases like methane would have bubbled out
of the rocks as the Earth’s core heated up. This “outgassing” still
happens on planets. It probably explains why there are lakes of
liquid methane and ethane on the surface of Titan, a moon of
Saturn.
When geologists started drilling for oil and gas, they began to
speculate about where it came from. Broadly speaking, the Americans
backed the fossil theory, while the outgassing heresy was
championed by some Russians, led by the great chemist Dmitri
Mendeleev, and later revived by the astrophysicist Tommy Gold. To
date, the fossil theory has worked well in predicting that oil and
gas would be found where ancient marine plankton had been trapped
in the shallow crust.
By contrast, a couple of wells drilled to more than 20,000 feet
in Sweden in the 1980s in a place where a meteorite had cracked the
granite crust, which might have let methane seep up from the molten
mantle far beneath, proved a costly failure. The Russians have kept
Mendeleev’s flame alive, however, and at a recent conference in
Kazan, in Russia, the idea that some gas fields are chemical, not
fossil, gained some support.
The meeting also discussed another idea: that a lot of natural
gas is made chemically but that life plays a part in gathering one
of the ingredients. The ocean floor accumulates not just the soft
bodies of plankton but also their shells and skeletons, made in
effect from dissolved carbon dioxide, which build up to thick
layers of carbonate rocks (such as the white cliffs of Dover in
England).
When the ocean floor is driven down deep into the molten mantle,
in the so-called subduction zones where continents are barging
their way over the oceanic crust, this carbonate gets heated and
pressurized. In 2004, Henry Scott of Indiana University and his
colleagues discovered that ideal conditions exist for this
carbonate to lose its oxygen and gain hydrogen instead, making
methane on a massive scale.
In effect, this would recycle the Earth’s carbon dioxide by
turning it back into the fuel from which it was made when burned or
breathed. Maybe this explains why so much methane bubbles up
through hydrothermal vents on the ocean floor. Moreover, a new paper by Vladimir Kutcherov of the Royal
Institute of Technology in Stockholm argues that this might also
explain why vast quantities of hydrated methane (known as fire-ice)
have been found under the seabed near the continental margins:
Perhaps it has come up from the mantle. Recently the Japanese
announced a successful pilot project to extract some of this
methane as a source of energy.
Dr. Kutcherov thinks the evidence “confirms the presence of
enormous, inexhaustible resources of hydrocarbons in our planet.”
If he is right—and America’s new Deep Carbon Observatory aims to
resolve the question in the next few years—natural gas may
effectively never run out.