Sixty-six million years ago, after a massive asteroid hit Earth with the explosive energy of roughly 1 billion nuclear bombs, a shroud of ash, dust and vaporized rock covered the sky and slowly rained down on the planet. As plant and animal species died en masse, tiny undersea amoebas called forams continued to reproduce, building sturdy shells out of calcium and other deep-sea minerals, just as they had for hundreds of millions of years. When each foram inevitably died — pulverized into seabed sediment — they kept a little piece of Earth’s ancient history alive in their fossilized shells.

For decades, scientists have studied those shells, finding clues about the ancient Earth’s ocean temperatures, its carbon budget and the composition of minerals spilling through the air and seas. Now, in a new study published today (Sept. 10) in the journal Science, researchers have analyzed the chemical elements in thousands of foram samples to build the most detailed climate record of Earth ever — and it reveals just how dire our current climate situation is.