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An exciting new application of the QMS instrument uses a high-energy laser fired through a modified microscope to open individual gas inclusions in ice. Ice from Greenland and Antarctica contain atmospheric gases that were captured in snow as it formed. The gases were retained as the snow turned into ice and formed bubbles. Analysis of these bubbles provides detailed information on the past composition of the atmosphere.
Sea-level changes, changes in solar activity, and, according to some astrophysicists, even the signals from distant supernovas, are also recorded in the ice. Compiling and studying this record helps us to evaluate current changes in the atmosphere and to predict future trends. Ice-core studies provide valuable information about the levels of human pollution, past climate patterns, sources of moisture, the altitude of the ice when it formed, frequency and magnitude of natural events, and biological activity at the ocean surface. Return to this point in index.
Air bubbles, amber, and dinosaurs
Ages of ice samples found on the Earth cover a span approaching 200,000 years. But how can we tell what the Earth s atmosphere was like before that? Recently, USGS scientists have used a gas QMS to determine the oxygen level of ancient samples of Earth s atmosphere from a most unlikely place amber. The fossilized resin of conifer trees, amber is interesting to scientists as a medium that traps insects, small animals, and plants, preserving them through geologic time for future study.
Amber --the fossilized resin of conifer trees--provides a unique means of protecting intricate samples of the past. This mosquito, lying trapped for 45 million years in a piece of amber, is almost perfectly preserved.
The recent extraction by scientists, of ancient DNA from organisms entombed in amber much like in the science-fiction novel and movie, Jurassic Park is an example of why scientists are intensely interested in amber. Minute bubbles of ancient air trapped by successive flows of tree resin during the life of the tree are preserved in the amber. Analyses of the gases in these bubbles show that the earth s atmosphere, 67 million years ago, contained nearly 35 percent oxygen compared to present levels of 21 percent. Results are based upon more than 300 analyses by USGS scientists of Cretaceous, Tertiary, and recent-age amber from 16 world sites. The oldest amber in this study is about 130 million years old.
This 84-million-year-old air bubble lies trapped in amber (fossilized tree sap). Using a quadrupole mass spectrometer, scientists can learn what the atmosphere was like when the dinosaurs roamed the earth.
The consequences of an elevated oxygen level during Cretaceous time are speculative. Did the higher oxygen support the now extinct dinosaurs? Their demise was gradual in the transition from late Cretaceous to early Tertiary times, as was the decrease in oxygen content of the atmosphere.
This chart shows a major decrease in oxygen content in the atmosphere from 35 percent to the present day level of 21 percent. This decrease occured about the same time that the dinosaurs disappeared--65 million years ago.
Recent methane emissions from Gulf Coast marshes
The Earth s atmosphere is still changing. Natural environmental processes (geological, biological, and geochemical) produce carbon dioxide (CO2) and methane (CH4). These gases, along with water vapor, are responsible for trapping heat at the Earth s surface.
Because biological processes are responsible for the production of methane in environments where organic matter ferments, wetlands (swamps, bogs, etc.) were previously the principal source of methane. Now, however, the combination of rice cultivation and cattle raising have taken over as the principal contributor. Studies of methane sources help us to understand their relative contributions and the factors that control the methane production and release to the atmosphere.
The studies show that when coastal wetlands are flooded by sea-level rise, salt marshes are inundated, up-slope brackish marshes become saltier, and some fresh marshes near the coast become brackish. Consequently, total methane emissions decrease because salt marshes do not produce as much methane as fresh marshes.
Fifteen miles inland from the Gulf of Mexico in a brackish marsh in Terrebonne Parish, Louisiana, methane emissions are collected in inverted buckets and measured with a portable gas analyzer. Using these measurements, scientists can determine one effect of global sea-level rise.
USGS studies of methane in Gulf Coast Louisiana indicate that brackish marshes emit between one-fourth and one-half the methane of the fresh marshes they replace during sea-level rise. The results of these local measurements in Louisiana can be used to project the world-wide effects of sea-level rise on methane emissions. By the year 2050, projected world-wide, sea-level rise will replace 50 percent of coastal fresh-water marshes with brackish water marshes. This will reduce the world s methane emissions by 2 percent. Return to this point in index.
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