Scientists have just found something incredible on the sea floor in the Arctic Ocean, something they weren’t expecting to find and quite surprised them when they stumbled upon it. Massive craters as wide as 12 city blocks were found there that scientists think were caused by huge eruptions of underground methane gas.

While some of the craters had been known to scientists since the 1990s, a new study maps out these features in tremendous detail, and researchers discovered far more craters than they had known about. They discovered 100 giant craters and thousands of smaller ones that date back about 11,600 years ago when the ie sheets were retreating, causing the release of these frozen gases under the sea floor.

It’s an incredible discovery that paints a colorful picture of the end of the Ice Age, as explosions ruptured the sea floor and Earth began the gigantic change that brought about the planet we know of today.

“The crater area was covered by a thick ice sheet during the last ice age, much as West Antarctica is today. As climate warmed, and the ice sheet collapsed, enormous amounts of methane were abruptly released. This created massive craters that are still actively seeping methane ” says Karin Andreassen, first author of the study and professor at CAGE Centre for Arctic Gas Hydrate, Environment and Climate. “But that is nothing compared to the blow-outs of the greenhouse gas that followed the deglaciation. The amounts of methane that were released must have been quite impressive.”