A huge find deep in the Arctic Ocean has caught the attention of the scientific community, and could help shed light on how the world looked as it emerged from the Ice Age and warmed to the planet we know today. Scientists discovered craters as wide as 12 city blocks on the sea floor, signs of gigantic eruptions caused by methane gas trapped underground.

Scientists first spotted a smattering of craters in the area in the 1990s, but this new study shows that there are a staggering 100 giant craters and thousands of smaller ones, and they all date back to about 11,600 years ago. They think that the explosions happened as the ice sheets started retreating, releasing the frozen gases from the sea floor.

The finding shows just what a volatile place the Earth was during this critical period in the planet’s history. Some of the craters were about a kilometer in width, indicating some truly epic explosions.

“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.”