Biogenic Natural Gas Linked to
Climate Change, Renewable Energy
1/25/2008 - University of Massachusetts Amherst - Natural gas
reservoirs in Michigan's Antrim Shale are providing new information
about global warming and the Earth's climate history, according to a
recent study by Steven Petsch, a geoscientist at the University of
The study is also good news for
energy companies hoping to make natural gas a renewable resource.
Results were published in the February 2008 issue of Geology.
found that carbon-hungry bacteria trapped deep in the rock beneath
ice sheets produced the gas during the ice age, as glaciers advanced
and retreated over Michigan.
"Bacteria digested the carbon
in the rocks and made large amounts of natural gas in a relatively
short time, tens of thousands of years instead of millions," says
"This suggests that it may be
possible to seed carbon-rich environments with bacteria to create
natural gas reservoirs."
The study also helps explain high levels of methane in the
atmosphere that occurred between ice ages, a trend recorded in ice
cores taken from Greenland and Antarctica.
"When the ice sheets retreated,
it was like uncapping a soda bottle," says Petsch. "Natural gas,
which is mostly methane, was released from the shale into the
This research can be used in current climate change models to
account for the effects of melting glaciers," says Petsch.
"Climate scientists haven't
focused on the role that geologic sources of methane play in global
Petsch used the chemistry of water and rock samples from the shale,
which sits like a bowl beneath northern Michigan, to recreate the
For most of its history, the
Antrim Shale contained water that was too salty to allow bacteria to
But areas rich in natural gas
showed an influx of fresh water that was chemically different from
"This water, which is similar
to meltwater from glaciers formed during the ice age, was injected
into the rock by the pressure of the overlying ice sheets," says
Glacial meltwater diluted the salt water already present in the
shale, allowing the bacteria to thrive and quickly digest available
The natural gas they produced
was chemically similar to the surrounding water and had a unique
carbon chemistry that proved its bacterial origin.
Petsch calculated that
trillions of cubic feet of natural gas were eventually stored in the
shale under pressure.
At least 75 percent of the gas was released into the atmosphere as
the ice sheets retreated, adding to methane from other sources such
as tropical wetlands.
While methane from the Antrim
Shale accounts for a small fraction of the rise in methane observed
between ice ages, there are many natural gas deposits that were
formed in the same geologic setting.
The cumulative effect may have
caused large emissions of methane to the atmosphere.
Klaus Nüsslein of the UMass Amherst microbiology department
analyzed DNA from water samples and identified bacteria capable of
breaking down hydrocarbons in the rock.
Other microbes were present
that produced methane from the break-down products. Both of these
groups can live without oxygen.
Identifying and studying the needs of these
microbes, which are capable of living deep in the Earth, is an
important step in creating new natural gas reserves.
Additional members of the team include post-doctoral researcher
Michael Formolo and undergraduate student Jeffrey Salacup of the
University of Massachusetts Amherst and Anna Martini, a professor of
geology at Amherst College.
The research was funded by the
National Science Foundation and the Research Partnership to Secure
Energy for America.