Did Meteorites Crashing Into Earth Form These Ancient Rocks?


A new study published in Nature Geoscience claims that some of the oldest rock on this planet were formed at very high temperatures resulted after meteorites crashed into Earth.

In Northwest Canada, there are felsic rocks (similar to granite) that date back to Earth’s early age. However, the composition in the felsic rocks from Canada is different from the felsic rocks at the middle of the continents. The authors used computer modeling, finding out that the different composition of the rocks from Northwest Canada would be the result of meteorite impacts.

Just right after Earth was formed, the Hadean era started (4.6 – 4 billion years ago). The authors explain in their paper the following:

“Given the predicted high flux of meteorites in the late Hadean, impact melting may have been the predominant mechanism that generated Hadean felsic rocks.”

Idiwhaa Gneisses

The 4.02-billion-year-old rocks studied were found in the Acasta Gneiss Complex in Canada, and are called Idiwhaa gneisses. In stable parts of continents, there are other old rocks which have a “tonalite–trondhjemite–granodiorite” composition. The Idiwhaa gneisses contain less silica and a lot more molecules which contain iron. This discovery made geologists realize that these rocks were formed after they partially melted older “mafic” rocks.

Using the data and complex calculations of melting points, temperature, composition and pressure, the researchers ran a computer simulation to see what happens if a 10-kilometer-wide meteorite hits a mafic crust at 12-17 km/s. The results showed that these rocks could form at a distance of 10-50 km from the impact and it also affected the mafic rocks at 3 km depth, making them melt and create the Idiwhaa gneisses.

Balz Kamber (Trinity College Dublin) was not involved in the study, but he believes that this theory can explain the different composition of Idiwhaa gneisses:

“The idea of making felsic melts by large or giant impacts seems plausible considering the high-energy nature of these events and the pockmarked ancient surfaces of other inner Solar System planets and moons.”

The authors based their study on computer modeling, with all the possible knowledge about Earth’s state in the Hadean era, which was quite hellish.


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