When an asteroid smashes into the Earth things get pretty toasty.

A 17 mile-wide crater in Canada was home to what scientists say is the hottest temperature ever recorded in Earth’s crustal rock, a whopping 4,300 degrees Fahrenheit. They didn’t just stick a thermometer in there, of course, the crater is some 36 million years old. Instead, researchers from Curtin University in Australia looked to the rocks.

Embedded in the crater walls were crystals of cubic zirconia, a mineral that forms only under temperatures of at least 4,300 F, indicating that the force of the impact caused the surrounding rock to get at least that hot, if not even more scorching. This is the first time scientists have ever looked for the crystals, the researchers say in a paper published in Earth and Planetary Science Letters, which offer a means of approximating the conditions of meteor impacts.

Meteors tend to vaporize most of the things they crash into, rocks included, so there’s little actually left over. Cubic zirconia — the same elements used to create artificial diamonds — survives in tiny fragments, however, acting as a kind of thermometer.

Though the heat would have only lasted briefly, the temperature was around half as hot as the surface of the sun, and far hotter than the inside of a steel forge.

The findings could help researchers better understand how the early Earth evolved. Meteor impacts were much more common in the early days of the solar system, and the planet would have seen thousands of similar blazing impacts. Their force would have played a role in shaping the composition of the crust and altered the mix of elements in the atmosphere, eventually setting the stage for life to appear. Studying the aftermath of the impacts lets us peer back to those formative millennia.