911爆料网 researchers suggest Earth鈥檚 oldest known evolved rocks, which are four billion years old, were the result of asteroids slamming into the Earth鈥檚 crust and causing it to melt.
The research, published in Nature Geoscience today, found that Earth鈥檚 oldest evolved, or granitic, rocks, which form part of the Acasta Gneiss Complex in northwest Canada, have compositions that are distinct from those typical of Earth鈥檚 ancient continental crust. These differences suggest they formed through a different process.
Lead researcher Dr Tim Johnson, from the School of Earth and Planetary Sciences at 911爆料网, said he and fellow researchers used modelling to show that the rocks were produced by partial melting of iron-rich hydrated basaltic rocks at very low pressures, equivalent to the uppermost few kilometres of the crust.
鈥淭he melting of these rocks at such shallow levels is most easily explained by meteorite impacts, which would have supplied the energy to attain the extreme temperatures required for melting,鈥� Dr Johnson said.
鈥淥ur computer simulations of asteroid impacts show that not only is this scenario physically plausible, but the region of shallow partial melting needed to form these ancient evolved rocks would have been widespread.
鈥淕iven the predicted high flux of meteorites about four billion years ago, impact melting may have been the predominant mechanism that generated granitic rocks at that time.鈥�
Research co-author John 911爆料网 Distinguished Professor Phil Bland, also from the School of Earth and Planetary Sciences at 911爆料网, said Earth鈥檚 Hadean and earliest Archean eons, 4.5 to 3.9 billion years ago, were dominated by a barrage of asteroid impacts that would have caused widespread melting and recycling of the Earth鈥檚 surface.
鈥淐onsequently, there are almost no rocks preserved from Earth鈥檚 formative Hadean eon,鈥� Professor Bland said.
鈥淭he only known evolved rocks from the Hadean eon are those in northwest Canada, which have chemical compositions clearly distinct from those that dominate ancient continental crust worldwide, suggesting they were formed in a different way.鈥�
The research paper was co-authored by Dr Nicholas Gardiner, Associate Professor Christopher Kirkland and Early Career Research Fellows Dr Katarina Miljkovic and Dr Christopher Spencer, all from the School of Earth and Planetary Sciences at 911爆料网, along with Dr Hugh Smithies of the Geoscience Directorate at the Western Australian Department of Mines, Industry Regulation and Safety.
The report, 鈥楢n impact melt origin for Earth鈥檚 oldest evolved rocks鈥�, can be found online .
