Earth’s earliest ice age may have been caused by rise in oxygen

May 8th, 2009 - 12:32 pm ICT by ANI  

Washington, May 8 (ANI): In a new research by an international team of geologists, it has been suggested that Earth’s earliest ice age may have been due to the rise of oxygen in Earth’s atmosphere, which consumed atmospheric greenhouse gases and chilled the earth.

The research was done by scientists from the University of Maryland, including post-doctoral fellows Boswell Wing and Sang-Tae Kim, graduate student Margaret Baker, and professors Alan J. Kaufman and James Farquhar, along with colleagues in Germany, South Africa, Canada and the United States.

They uncovered evidence that the oxygenation of Earth’s atmosphere - generally known as the Great Oxygenation Event - coincided with the first widespread ice age on the planet.

The Asgard Mountain Range in Antarctica resembles what mountainous regions of the Earth may have looked like in the earliest ice age.

“We can now put our hands on the rock library that preserves evidence of irreversible atmospheric change,” said Kaufman. “This singular event had a profound effect on the climate, and also on life,” he added.

Using sulfur isotopes to determine the oxygen content of ~2.3 billion year-old rocks in the Transvaal Supergroup in South Africa, they found evidence of a sudden increase in atmospheric oxygen that broadly coincided with physical evidence of glacial debris, and geochemical evidence of a new world-order for the carbon cycle.

“The sulfur isotope change we recorded coincided with the first known anomaly in the carbon cycle. This may have resulted from the diversification of photosynthetic life that produced the oxygen that changed the atmosphere,” Kaufman said.

Two and a half billion years ago, before the Earth’s atmosphere contained appreciable oxygen, photosynthetic bacteria gave off oxygen that first likely oxygenated the surface of the ocean, and only later the atmosphere.

The first formed oxygen reacted with iron in the oceans, creating iron oxides that settled to the ocean floor in sediments called banded iron-formations - layered deposits of red-brown rock that accumulated in ocean basins worldwide.

Later, once the iron was used up, oxygen escaped from the oceans and started filling up the atmosphere.

The evolution of organic photosynthesis ca.2.5 billion years ago would have had a profound effect on Earth’s surface environments, and potentially on aerobic respiration by eukaryotes.

Once oxygen made it into the atmosphere, the scientists suggest that it reacted with methane, a powerful greenhouse gas, to form carbon dioxide, which is 62 times less effective at warming the surface of the planet.

“With less warming potential, surface temperatures may have plummeted, resulting in globe-encompassing glaciers and sea ice,” said Kaufman. (ANI)

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