One of the more startling recent discoveries about Earth's history is that some 2.3 billion years ago the entire planet was covered in ice, more than a mile thick at the equator. While the discovery has not been (to my knowledge) disputed, nobody could figure out why. Now, a group of California Institute of Technology students and scientists think they've found the reason:

Several graduate students, along with supervising professor Joe Kirschvink, have released a paper presenting their explanation of what caused "Snowball Earth," a periodic deep freeze of Earth's atmosphere that has been theorized for years. The Caltech team argues that 2.3 billion years ago, cyanobacteria, or blue-green algae, gained the ability to break down water, which in turn released a flood of oxygen into the atmosphere.

That oxygen reacted with the atmospheric methane, which insulated the Earth at the time, and broke it down. While the oxygen-methane reaction created the greenhouse gas carbon dioxide, the protective nature of the barrier cracked.

As always, the findings are already being debated, but it's good to see new discoveries and theories being made about one of the most curious episodes in our planet's history.