The earth is about 4.6 billion years old (with apologies to young earthers). During that time, the climate has changed numerous times, including several episodes of freezing that put the earth into virtual hibernation.

The processes that led to "Snowball Earth," where miles of ice have entirely covered the planet have only been dimly understood. But scientists have found an important clue; there's a lot less rock on the surface than there should be. Simple erosion cannot account for the missing miles of crust.

Los Angeles Times:

“There must have been some sort of special event in Earth’s history that led to widespread erosion,” said Steve Marshak, a geologist at the University of Illinois at Urbana-Champaign who studies what has come to be known as the Great Unconformity.

New research suggests it was something special indeed. Scientists propose that several freak episodes of global glaciation scoured away miles of continental crust, obliterating a billion years of geologic history in the process.

Scientists call it "The Great Unconformity" and it throws conventional theories about climate change for a loop.

Today, however, researchers have come to accept the outlandish notion that, a few times in its 4.6-billion-year history, the planet froze over and became a “Snowball Earth.” Now Keller and his colleagues hope to convince their peers that the glaciers that crawled across the continents between 720 million and 580 million years ago were responsible for the Great Unconformity.

Since there are so few rocks from that period, the researchers had to look for other kinds of clues to figure out what happened. They reasoned that the missing layers probably went through the full geologic spin cycle: They would have been broken down into sediment and washed out to sea, then deposited on the ocean floor and recycled into the mantle during subduction before finally melting into the magma that feeds volcanoes.

If so, a record of this activity should hide in tiny time capsules called zircons. These indestructible crystals grow in magma, and they contain the elements oxygen and hafnium. Oceanic and continental crust have distinct signatures of these elements. Therefore, a huge spike in the amount of recycled continental material should have left a clear chemical signal in zircons that formed at that time — and it did.

During these episodes of global glaciation, almost all life is snuffed out. So the question of what has been causing global climate change for the last half billion years becomes relevant to us.

What we know is that it almost certainly wasn't carbon dioxide or any other trace gas in the atmosphere that was responsible. It appears that levels of CO2 have fluctuated modestly over that period of time and would have little or nothing to do with creating a "snowball earth" or any other radical alteration of the climate.

The question then becomes, why would greenhouse gases have much to do with climate change today? There is no doubt that there is a correlation between greenhouse gases and temperature, but no supercomputer in the world could predict any kind of radical alteration of the climate because X amount of CO2 was spewed into the atmosphere. There are many other factors at work in climate change - none of them man made - that to assign CO2 as a culprit for global warming is absurd.

A lack of CO2 in the atmosphere did not lead to "snowball earth." Why should an overabundance of CO2 lead to catastrophic global warming?