Why Early Earth Didn't Freeze Over Still a Mystery - Yahoo! News
Global warming gases cannot explain why Earth was not frozen billions of years ago when the sun was cooler, researchers say.
In the Archean Eon about 2.5 billion to 4 billion years ago, before the first advanced life appeared on the planet, the sun was only about 70 percent as bright as it is today. This means the amount of heat felt on Earth was much less, and Earth's surface should have been frozen.
...The contradiction between the cold Earth that apparently should have existed and the temperate Earth that apparently did exist is known as the "faint young sun paradox." Until now, the most popular explanation for this enigma was that there was a higher concentration of "greenhouse gases" such as carbon dioxide in the atmosphere than today. These gases absorb heat from the sun, helping warm the planet."Just like the average temperature of Earth is getting higher today because there are more greenhouse gases than there were before the Industrial Revolution, or even before the invention of agriculture, the presence of high concentrations of carbon dioxide and methane should have kept the early Earth warm," Pope said. [Early Earth Was Purple]
For greenhouse gases to explain the faint young sun paradox, their concentrations would need to have been extremely high, hundreds to thousands of times as much as today.
"If levels of carbon dioxide were that high, they would be recorded in ancient soils and sediments in the rock record," Pope said. "If levels of methane were that high, they would actually form a kind of organic haze in the atmosphere that blocks the sun's rays and would counteract its properties as a greenhouse gas."
Now scientists analyzing relatively pristine 3.8-billion-year-old rocks from Isua find no evidence that greenhouse gas levels were high enough to explain the faint young sun paradox, further deepening the mystery, Pope told LiveScience.
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