Study links continent creation to 200-million year galactic comet cycle

Amazing stuff! This could be a consequential study, if confirmed! May partially explain why some planets remain fireballs for long periods of time.

E.g. how much of the travel of the Solar System through the Milky Way galaxy contributes to global warming/climate change?

"Geologists have discovered a long-term cycle that may connect the formation of Earth’s continents to increased comet impacts and the planet’s journey through the galaxy. The team connected fluctuations in tiny grains in stable parts of the crust to the times our solar system passed through the galaxy’s spiral arms. ...
the scientists observed patterns that suggested crust production spikes every 170 to 200 million years. Intriguingly, this was consistent across both cratons, even though they’re at opposite ends of the planet, indicating the cycle isn’t caused by local factors. ...

The team says that when our [Solar System] moves into one of the spiral arms, gravitational influences of the higher density of material can shake material loose from the Oort cloud, which surrounds the solar system. These objects can then migrate towards the inner solar system in the form of comets, increasing the chances of collisions with Earth.

Comets tend to travel at much higher speeds than asteroids, and the team says that when they strike Earth, they excavate and melt large portions of the mantle, causing the molten rock to rise to the surface and float on top of the denser mantle material. As these sections cool, they form “seeds” of continental crust, that can grow over time as more magma sticks to them. ..."

"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. ..."

From the abstract:

"Although there is evidence for periodic geological perturbations driven by regular or semi-regular extra-terrestrial bombardment, the production of Earth’s continental crust is generally regarded as a function of planetary differentiation driven by internal processes. We report time series analysis of the Hf isotopic composition of zircon grains from the North Atlantic and Pilbara cratons, the archetypes of Archean plate tectonic and non-plate tectonic settings, respectively. An ~170–200 m.y. frequency is recognized in both cratons that matches the transit of the solar system through the galactic spiral arms, where the density of stars is high. An increase in stellar density is consistent with an enhanced rate of Earth bombardment by comets, the larger of which would have initiated crustal nuclei production via impact-driven decompression melting of the mantle. Hence, the production and preservation of continental crust on the early Earth may have been fundamentally influenced by exogenous processes. A test of this model using oxygen isotopes in zircon from the Pilbara craton reveals correlations between crust with anomalously light isotopic signatures and exit from the Perseus spiral arm and entry into the Norma spiral arm, the latter of which matches the known age of terrestrial spherule beds. Our data support bolide impact, which promoted the growth of crustal nuclei, on solar system transit into and out of the galactic spiral arms."

Study links continent creation to 200-million year galactic comet cycle

Did transit through the galactic spiral arms seed crust production on the early Earth? (open access)

Comet impacts formed continents when Solar System entered galactic arms New Curtin [university, Australia] 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.