Comet impacts formed continents when Solar System entered galactic arms

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New Curtin research has found evidence that Earth’s early continents resulted from being hit by comets as our Solar System passed into and out of the spiral arms of the Milky Way Galaxy, turning traditional thinking about our planet’s formation on its head.

The new research, published in Geology, challenges the existing theory that Earth’s crust was solely formed by processes inside our planet, casting a new light on the formative history of Earth and our place in the cosmos.

Lead researcher Professor Chris Kirkland, from the Timescales of Mineral Systems Group within Curtin’s School of Earth and Planetary Sciences, said studying minerals in the Earth’s crust revealed a rhythm of crust production every 200 million years or so that matched our Solar System’s transit through areas of the galaxy with a higher density of stars.

“The Solar System orbits around the Milky Way, passing between the spiral arms of the galaxy approximately every 200 million years,” Professor Kirkland said.

“From looking at the age and isotopic signature of minerals from both the Pilbara Craton in Western Australia and North Atlantic Craton in Greenland, we see a similar rhythm of crust production, which coincides with periods during which the Solar System journeyed through areas of the galaxy most heavily populated by stars.”

“When passing through regions of higher star density, comets would have been dislodged from the most distant reaches of the Solar System, some of which impacted Earth.

“Increased comet impact on Earth would have led to greater melting of the Earth’s surface to produce the buoyant nuclei of the early continents.”

Professor Kirkland said the findings challenged the existing theory that crust production was entirely related to processes internal to the Earth.

“Our study reveals an exciting link between geological processes on Earth and the movement of the Solar System in our galaxy,” Professor Kirkland said.

“Linking the formation of continents, the landmasses on which we all live and where we find the majority of our mineral resources, to the passage of the Solar System through the Milky Way casts a whole new light on the formative history of our planet and its place in the cosmos.”

Professor Kirkland is affiliated with The Institute for Geoscience Research (TIGeR), Curtin’s flagship Earth Sciences research institute.

Also contributing to the study were researchers from the University of Lincoln, the Astromaterials Research and Exploration Science Division within NASA’s Johnson Space Center and the Geological Survey of Western Australia.

The full research paper, ‘Did transit through the galactic spiral arms seed crust production on the early Earth?’ was published in the journal Geology and can be found online here.