Astronomers find the shocking reason that shaped Earth’s continents

Earth is the only one A planet known to have continents. in New study Published on August 23 in the magazine geologyResearchers are proposing unexpected seeds for the formation of the first continents on our world – comets launched into our solar system as they passed through the spiral arms of the Milky Way.

Here’s the background – Unlike any other known planet, the Earth’s surface possesses both Continents and oceans. Continental crust is less dense and thicker than oceanic crust, causing it to essentially float higher than oceanic crust on the Earth’s dense mantle.

The presence of continents on Earth greatly affected the planet’s atmosphere, oceans, climate and the spread of life. For example, runoff from continents is the primary source of a number of key ocean nutrients, such as phosphorous, which is needed to create DNA and other biological building blocks.

Previous research revealed cycles in continental crust production. Scientists generally believe that these cycles are associated with the regular birth and destruction of giant continents on the Earth’s surface due to the movement of tectonic plates – the erosion, collision and submersion of the giant plates of rock that currently make up the Earth’s surface.

However, these cycles are also seen in some of Earth’s oldest rocks, when plate tectonics may not have been present.

Our location in the Milky Way was affected when comets collided with the Earth and formed our continents.bad. Kirkland and others.

What did the scientists do? – In the new study, the researchers analyzed data from two places with the oldest history of continents preserved on Earth – the North American Craton in Greenland and the Pilbara Craton in Western Australia. (Cratons are giant stable clumps of Earth’s crust that make up the cores of continents.)

The decay of uranium in zircon crystals helped scientists determine details about the continental composition at both sites, over a time period from about 2.8 billion to 3.8 billion years ago. The isotopes of hafnium found within these crystals have also helped identify times of magma flows associated with crust production.

By looking at massive amounts of data from large amounts of rock, the researchers discovered a rhythmic pattern in the formation of continental crust about 170 million to 200 million years old. They detected a similar pattern when looking at oxygen isotopes, and support their findings. “This pattern can only be determined from large data sets,” said the study’s lead author Chris Kirkland،, a time geologist at Curtin University in Perth, Australia inverse.

What did they find? – This pattern corresponds to the amount of time it takes the Solar System to pass through one of the four main spiral arms of the Milky Way, where the density of stars and interstellar clouds is high, as it completes an orbit around the galactic core.

The gravitational effect of the spiral arms can move comets from the Oort cloud at the outer reaches of the solar system inward at Earth and other planets. Scientists argue that such a cometary bombardment may have excavated huge amounts of rock from the Earth’s surface, loosening the underlying mantle rock and melting, like the crackling of a cork on a bottle of champagne. The generation of these floating molten rocks may in turn have produced the continents.

“While the impacts are seen as catastrophic events, they also shaped the evolution of our planet, and it seems our continents would not have developed the way they did without them,” Kirkland says. “Our planet is connected to the galactic structure.”

The researchers found more evidence for this idea within globular layers, which are rock formations caused by cosmic influences. These deposits of small balls formed either from molten rock that was expelled during the impact or from vaporized rock that condensed and rained down after the impact. They pointed out that the ages of the globular family in Australia and South Africa correspond to the movement of the solar system in the spiral arm Norma about 3.25 billion to 3.45 billion years ago. They noted that determining the ages of more football families could add more evidence.

The continents we know today could have been formed by external forces. Ilbusca / Digital Vision Vectors / Getty Images

“It has become clear that the solar system and the Earth did not form on their own, but with influence from outside,” says study co-author Phil Sutton, a planetary scientist at the University of Lincoln in England. inverse. “We need to redirect our gaze to the outside rather than just focus on the internal mechanisms.”

Although impacts on Earth occur more often from rocky bodies of the asteroid belt than from comets in the Oort cloud, collisions from the Oort cloud will strike with much greater energy. This is because near-Earth asteroids are “going in the same direction as Earth,” says Sutton. “So when there is an effect from this group, the difference in velocity is much less.”

Imagine cars traveling on a multi-lane road in the same direction. If a car collides with another car next to it, the “relative collision velocity is very low,” he explains.

However, if there was a junction across that road and one car collided with another at that junction at 90 degrees, “the damage would be much greater,” says Sutton, “which is basically what happens with comets compared to asteroids.”

In addition, the gravitational pull of the Sun and Jupiter makes it difficult to hit near-Earth asteroids from their orbits. In contrast, the Sun exerts a weak influence on comets in the Oort cloud, making them more susceptible to turbulence, Sutton explains.

The researchers stress that the time frames during which these giant impacts occur are “enormous and in no way pose a danger to us,” says Sutton. “For example, dinosaurs were on the planet about the same time it takes to go from one spiral arm to another, which is hundreds to thousands of humans longer.”

Interestingly, “life is thought to have arisen at the times when we report periodic crust production,” says Sutton. “Is this a coincidence, or is it the spark that ignited the explosion of life on this planet?”

What’s Next? – It is possible that the role of forcings in continental crust production has declined over time due to the accelerated decline in the mean size and number of potential forcings with the evolution of the solar system. Scientists note that the emergence of plate tectonics would also have started to play a more important role in the production of the continent on Earth.

“It would be great to see a similar pattern in the timing of lunar collisions,” Kirkland says. “You can expect the same rate of impact on the moon as well.”