The Mistastin Lake crater was created about 36 million years ago, when an asteroid hurtled into what is now the province of Newfoundland and Labrador in Canada. As Aylin Woodward reports for New Scientist, a recent study has found that the impact of the space debris briefly heated the surrounding rocks to 2370 °C (4298 °F)—the hottest temperature ever recorded for rocks on the Earth’s surface.
An international team of researchers gauged the ancient temperatures created by the powerful blast thanks to the presence of a tough crystal at the site of the impact known as zircon. Back in 2011, Michael Zanetti, now a post-doctoral researcher in earth sciences at Western University in Ontario, was exploring the site when he noticed unusually shiny rock lying on the ground. As Zanetti tells Emily Chung of the CBC, when he put a slice of the rock under a microscope, he observed “this kind of weird-looking" grain of zircon—a mineral composed of zirconium, silicon and oxygen.
The grain was surrounded by a brown ring, which analysis revealed to have once been cubic zirconia, a crystal that only forms when zircon is heated to at least 2370 °C— “halfway to the temperature at the sun’s surface,” as Woodward notes. Researchers were consequently able to conclude that the asteroid strike at Mistastin Lake created temperatures that were at least this high. The results of their study were published in the journal Earth and Planetary Science Letters.
Nicholas Timms, a senior lecturer at Curtin University in Perth, Australia and lead author of the study, tells Woodward that this is the first time cubic zirconia has been used to trace temperatures that scorched the Earth’s surface millions of years ago. “Nobody has even considered using zirconia as a recorder of temperatures of impact melts before,” he says. “This is the first time that we have an indication that real rocks can get that hot.”
The team’s findings are an important breakthrough. The task of measuring the heat created by ancient asteroids has posed quite a challenge for past researchers. As George Dvorsky explains for Gizmodo, minerals usually vaporize when they are exposed to extremely high temperatures, leaving few clues for scientists of the modern era. The presence of cubic zirconia, however, shows that “extremely high melt temperatures can be achieved, even in moderate-sized impact events, and are not limited to giant, basin-forming impacts,” the authors of the study write.
“Moderate-sized” impacts like the one at Mistastin Lake were in fact common during the Late Heavy Bombardment period, which started some 3.8 billion years ago and may have helped deposit water on the Earth’s surface. Because of this, the new findings at Mistastin Lake may help scientists glean a better picture of conditions on our planet during its early years, before it became hospitable to human life.