Earth's ancient atmosphere trapped in rocks

Fog streaming over the Namibian desert in Africa may be responsible for transporting sulfur from the ocean to terrestrial rocks. Researchers believe it may also be the place where the sulfur is oxidized by ozone or hydrogen peroxides

July 13, 2000
Web posted at: 12:17 p.m. EDT (1617 GMT)

By Environmental News Network staff

Scientists on a quest to characterize the long-term chemical evolution of Earth's atmosphere need to understand what the air was like millions of years ago. To do this, they've come to realize they can leave no stone unturned.

Uncovering the signature of so-called "fossil air" in terrestrial rocks and sediment is reported for the first time in today's issue of Nature.

The signature is in the form of an irregular isotope of oxygen that gets transferred from ozone and other atmospheric oxidants to sulfate during the oxidation of reduced sulfur gases, according to Huiming Bao, a geochemist at the University of California, San Diego.

These oxidized gases become incorporated into sulfate minerals in solid deposits on Earth's surface. Scientists have searched for this signature for decades. They finally found it in gypsum deposits from the Namibian desert in Africa and in volcanic ash deposits in Nebraska and South Dakota.

Detection of the isotope anomaly gives scientists an important new tool to answer questions about the composition of Earth's early atmosphere, the atmospheric processes of ancient volcanic eruptions, past ocean circulation patterns and early biological productivity.

"No one has found a way you can measure the ancient atmosphere in solid examples," said Mark Thiemens, a professor of chemistry at the University of California at San Diego. "Ice cores don't go back far (about 250,000 years). Now one can go back hundreds of millions of years or billions of years."

Mark Thiemens, a professor of chemistry at the University of California at San Diego, believes studying the long-term chemical evolution of Earth's atmosphere will prove useful in discussions of global warming

Thiemens said the ability to characterize the long-term chemical evolution of Earth's atmosphere will help scientific, economic and political leaders in their discussions of global warming.

"One always hears the argument, 'Isn't this (global warming) all part of a natural cycle?'" he said. "To answer that question, you really want to have a large-scale record. This will give it to us. We really need to understand the past to understand the present and the future."

The scientists believe the signatures in the volcanic ash from Nebraska and South Dakota could provide geologists with more information about the chemistry of volcanic plumes and the nature of the eruptions that produced them.

Because the coast off central Namibia is a major zone of upwelling with intense biological activity, the researchers were able to tie the anomalous sulfate deposits to the activity of nearby sulfur-producing marine micro-organisms and the unique desert environment that is able to preserve the signature.

However, the upwelling current may not have been constant during the past several millions of years and may be intimately tied to the change of ancient climate conditions. The researchers said that if such a connection can be made, it might provide insight to previous ocean circulation and biological productivity.

The long-term chemical evolution of the atmosphere of other planets such as Mars may also be preserved in terrestrial sediment, said Thiemens. As such, presumed Martian meteorites and future samples returned from Mars may provide information about the chemical evolution of the Martian atmosphere.

Copyright 2000, Environmental News Network, All Rights Reserved

Warming drops Great Lakes toward historic lows
April 26, 2000
America's most wanted: Power plants urged to clean up their act
April 21, 2000
Soot eats clouds, turns up global thermostat
May 12, 2000
Arctic warming signals dire straits for birds
April 5, 2000

Plants spread secrets about climate change
Little ice age holds big climate clues
Historic global warming linked to methane release
El Nino's history archived in sediment
Martian meteorite disappoints scientists

Nature
Mark Thiemens
ENN's Global Warming
EPA Global Warming Site

Note: Pages will open in a new browser window

External sites are not endorsed by CNN Interactive.