Why ancient earth wasn't an iceball

One of the great science mysteries might finally have been solved - why wasn't ancient Earth covered in ice?

Back in the early days of our planet, it was mostly covered in seas. Since the Sun was warming much less back then, it has puzzled scientists why these seas were not frozen. Now Danish and US scientists offer an explanation.

Why Earth Wasn't One Big Ball of Ice 4 Billion Years Ago When Sun's Radiation Was Weaker

Scientists have solved one of the great mysteries of our geological past: Why Earth's surface was not one big lump of ice four billion years ago when Sun radiation was much weaker than today. Scientists have presumed that Earth's atmosphere back then consisted of 30 percent CO2 trapping heat like a greenhouse. However, new research shows that the reason for Earth not going into a deep freeze at the time was quite different.

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Now, however, Professor Minik Rosing, from the Natural History Museum of Denmark, and Christian Bjerrum, from the Department of Geography and Geology at University of Copenhagen, together with American colleagues from Stanford University in California have discovered the reason for "the missing ice age" back then, thereby solving the Sun paradox, which has haunted scientific circles for more than 40 years.

Professor Minik Rosing explains: "What prevented an ice age back then was not high CO2 concentration in the atmosphere, but the fact that the cloud layer was much thinner than it is today. In addition to this, Earth's surface was covered by water. This meant that the Sun's rays could warm the oceans unobstructed, which in turn could layer the heat, thereby preventing Earth's watery surface from freezing into ice. The reason for the lack of clouds back in Earth's childhood can be explained by the process by which clouds form. This process requires chemical substances that are produced by algae and plants, which did not exist at the time. These chemical processes would have been able to form a dense layer of clouds, which in turn would have reflected the Sun's rays, throwing them back into the cosmos and thereby preventing the warming of Earth's oceans.

So, the lack of life, which in turns leads to less clouds, and the liquid surfaces, are the reasons why the water didn't freeze, even when the heat from the Sun were lower.

This is a much better explanation than the earlier proposed explanation (also mentioned in the ScienceDaily article) that the CO₂ levels were much higher back then. The new investigation which led to the new explanation demonstrates that the CO₂ levels back then were higher, but nowhere nearly as much higher as the old explanation would have required.

The actual study is behind a paywall at Nature, but if you have access, you can find it here.