The fist-sized, glassy rock collected by Micheal Zanetti at the Mistastin Lake Crater. Credit: Micheal Zanetti
About 38 million years ago, an estimated city-sized asteroid raged against the Earth and exploded mid-air close to what is nowadays Labrador in the northern Canada. The impact was so strong that it created the Mistastin Lake Crater which is 16 km (9.9 mi) in diameter. It was believed the original crater spanned 28 km (17 mi) in diameter. Great impacting force comes with intense explosion and high temperature. According to a recent publication in the journal Earth and Planetary Science Letters, the meteor strike heated rocks in the vicinity to at least 2370 °C (4298 °F), the highest ever evidenced on the surface of the Earth.
Rocks are constantly exposed to extreme temperatures deep under the Earth’s surface. Take granite, for example, it is one of the most common rocks found in the crust (the base layer of the continents and the outer layer of earth’s rocky body) and has a melting point of 1215–1260 °C (2219–2300 °F). Beneath the crust lies the mantle, whose temperatures range from 500 to 900 °C (932 to 1652 °F) at the upper border with the crust; to over 4000 °C (7230 °F) at the boundary with the core. At such high temperature, rocks start to melt, forming the large magma reservoirs that feed the Earth's volcanoes. Without the pressure, it is almost impossible to have such high temperature on the surface of the Earth.
When Michael Zanetti, a post-doctoral researcher at Western University in London, Ontario, found a rock sample during his a mock "mission to the moon" at the Mistastin Lake Crater In 2011, he never imagined that it would turn out to be a significant scientific discovery. The crater is often used by space scientists to simulate the far side of the moon because of their shared geology and mineralogy features. The Canadian Space Agency funded efficiency studies to evaluate the working dynamics between an astronaut and robotic rover on the moon surface. That was when Zanetti, then a Ph.D. student, first set eyes on this strange looking rock.
The zircon grain at the center of the rock. Credit: Micheal Zanetti
Geochemists from Curtin University in Australia found naturally occurring cubic zirconia in the rock sample. Both Zircon and cubic zirconia are zirconium dioxide in nature. But they have the entirely different crystalline structure: zircon has a tetragonal while zirconia has a more densely packed cubic structure. Zirconia, often a cheap diamond substitute, are mostly artificially produced by heating up naturally existing zircon. Because the minimum temperature for the transformation to happen is 2370°C or 4298°F, the researchers suggested that the impact of the Mistastin Crater asteroid must have heated the surrounding rocks to that temperature if not higher. While most other rocks evaporated due to low melting/evaporation point, the zircon containing rocks survived and underwent a structural transformation. It was estimated that the extreme temperature could have lasted from seconds to minutes. It is almost twice as high as the temperature of lava from a volcano.
“The discovery is interesting to researchers because up until now, they've relied on computer models to estimate the temperatures produced in an asteroid impact like this, but didn't have any good physical evidence to back those up,” said Micheal Zanetti, a co-author of the recent publication. "This closes the gap a little bit."
Top Ten Meteor Strikes on Earth. Credit: TopTenz