Connecting small grains of the Earth with our own galactic environment. In a study published in the journal Geology, an international team of scientists has identified a rhythm in the production of early continental crust and, according to their conclusions, everything points to a truly grandiose driving mechanism that could have formed our Earth’s crust.
The surface of the planet, we initially imagined as something formed by processes always immersed within the Earth, but it is clear that our planet has felt the effects of its cosmic environment in its historical trajectory, which includes periodic changes in the Earth’s orbit , variations in the Sun’s emission, gamma-ray bursts and, of course, asteroid impacts.
How was the earth’s crust formed?
So far, Earth is the only planet we know of that has active continents and plate tectonics. These features have helped make Earth hospitable to life because they influence the atmosphere, hydrosphere, and biosphere.
“As geologists, we normally think that the internal processes of the Earth are really important for the evolution of our planet,” explains isotope geologist at Curtin University in Australia and co-author of the work, Chris Kirkland. “But we can also think on a much larger scale and look at extraterrestrial processes and where we fit into the galactic environment.”
The oldest rocks on Earth
In their study, the researchers analyzed zircon crystals deposited in the North American Craton in Greenland and the Pilbara Craton in Western Australia, two regions that preserve some of Earth’s oldest continental crust, dating to the eon Archaic. By measuring the decay of uranium within the crystals, they were able to establish a timeline for the formation of cratons, which spans from about 2.8 to 3.8 billion years ago. They also looked at hafnium isotopes, which allowed them to identify juvenile magma inflow times associated with crust production. The analysis revealed a longer period, a 200-million-year wobble in the data, which correlates with Earth’s motion through the Milky Way; something that was also reflected in the oxygen isotope data, which reinforced their results.
“The study of minerals in the Earth’s crust revealed a rate of crust production every 200 million years that coincided with the transit of our solar system through areas of the Milky Way with a higher density of stars,” Kirkland said.
The solar system rotates around the center of the galaxy slightly faster than the spiral arms, periodically passing through and overtaking them. Perhaps cosmic encounters with more stars, gas and dust within the spiral arms affected the young planet, the team suggests. Some of those encounters would have sent comets zooming in on the inner solar system, and a fraction of those icy denizens would have collided with Earth, the researchers propose.
The resulting magma would have naturally separated into a denser part, the precursor to more oceanic crust, and a lighter, buoyant liquid that eventually became continental crust , the researchers suggest.
The team hopes their findings will prompt further investigation into how forces outside the solar system have shaped the planet we live on.
“The findings challenged the existing theory that crust production was entirely related to internal Earth processes,” continues Kirkland. “Our study reveals an exciting link between geological processes on Earth and the motion of the solar system in our galaxy. Linking the formation of the continents, the land masses on which we all live and where we find most of our mineral resources, to the passage of the solar system through the Milky Way sheds a whole new light on the formative history of our planet. planet and its place in the cosmos.
Referencia: C.L. Kirkland et al. Did transit through the Galactic spiral arms seed crust production on the early Earth? Geology, published online August 23, 2022; doi: 10.1130/G50513.1