Astronomers reveal what prompted the Earth to form the continents it is today

Unlike any other planet, the Earth's surface possesses both continents and oceans. Continental crust is much less dense and denser than oceanic crust, which causes it to essentially float higher than oceanic crust.

The presence of continents on Earth has greatly influenced the planet's atmosphere, oceans, climate, and proliferation. For example, runoff from the continents is the main source of some important nutrients for the ocean, such as phosphorus, which is needed to make DNA and other biological building blocks.

Previous research has discovered cycles in the production of continental crust. Scientists often think that these cycles are related to the frequent birth and destruction of supercontinents on the Earth's surface by plate tectonics - the drift, collision, and subduction of rock plates giants that made the Earth's surface what it is today.

However, these cycles are also seen in some of the Earth's oldest rocks, where plate tectonics may not have existed yet.

In the new study, published in the journal Geology, researchers analyzed data from two of the earliest historical repositories of the Earth's continents - the North American crater in Greenland and the North American crater in Greenland. Pilbara crater in Western Australia.

The decay of uranium in zircon crystals helped scientists pinpoint the details of continental formation at both sites, which spanned from about 2.8 billion to 3.8 billion years ago. The isotopes of hafnium inside these crystals also help determine the timing of the magma fluxes involved in crust production.

By looking at vast amounts of data from a large amount of rock, the researchers discovered a pattern in the formation of continental crust that is about 170 million to 200 million years old. "Only through large data sets can this pattern be identified," said lead author Chris Kirkland, a geochronologist at Curtin University in Perth, Australia.

This pattern corresponds to the time it takes for the Solar System to pass through one of the four main spiral arms of the Milky Way, which has a high density of stars and interstellar clouds, when it completes. an orbit around the center of the galaxy.

The gravitational influence of the spiral arms can pull comets from the Oort cloud in the outermost regions of the Solar System into Earth and other planets. Scientists think that such Cometary impacts may have ejected large amounts of rock from the Earth's surface, resulting in the underlying rock being compressed and melted, and may have sown the seeds for the eruption. forming continents.

"These impacts have shaped our planet's evolution, and it's unlikely that our continents would have evolved the way they do today without the collisions," said Kirkland. like this. From this it can be seen that our planet is connected to the structure of the galaxy."

The researchers found more evidence for this idea inside furrows of spherules, which are rock formations created by cosmic impacts. These blocks contain small spheres that are formed from molten rock discharged during an impact or from evaporative rock that condenses and flows out after an impact. They note that the age of the spherule beds in Australia and South Africa matches the motion of the Solar System into the Norma spiral arm about 3.25 billion to 3.45 billion years ago. They note that pinpointing the age of more spherule beds may add further evidence to this claim.

Although Earth is impacted more frequently by the asteroid belt rocks than by comets in the Oort cloud, the Oort cloud collisions will generate more energy. This is because near-Earth asteroids "are moving in the same direction as Earth," said Phil Sutton, a planetary scientist at the University of Lincoln, UK, who co-authored the study.

Imagine cars traveling on a multi-lane road in the same direction. If a car crashes into another vehicle next to it, "the relative collision velocity is quite low," he explains.

However, if an intersection crosses this road and a car hits another vehicle at this intersection at a 90-degree angle, "the damage will be greater," Sutton said.

The role of impacts in continental crust formation is likely to decrease over time due to an exponential decline in the average size and number of potential actors as the Solar System develops. The scientists note that over time, the emergence of tectonic plates also began to play a more important role in the production of continents on Earth.