Researchers Argue Earth Formed Much Faster Than Believed, Suggest More Planets C...

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An anonymous reader quotes this report from the Washington Post: In a new study released in Nature this week, researchers state that Earth formed within just 3 million years. That's notably faster than previous estimates placing the timeline up to 100 million years.... "We can also predict that if other planets formed ... by the same mechanism, then the ingredients required for life such as water, should be present on other planets and other systems, so there's a greater chance that we have water worlds elsewhere in the galaxy," said Isaac Onyett, lead author of the study and Ph.D. candidate at the University of Copenhagen.

The authors assert that this rapid genesis occurred through a theory called pebble accretion. The general idea, according to co-author and cosmochemist Martin Bizzarro, is that planets are born in a disk of dust and gas. When they reach a certain size, they rapidly attract those pebbles like a vacuum cleaner. Some of those pebbles are icy and could provide a water supply to Earth, thought of as pebble snow. This would have led to an early version of our planet, known as proto-Earth, that is approximately half the size of our present-day planet. (Our current rendition of Earth likely formed after a larger impact about 100 million years later, which also led to the formation of our moon....)

The team determined the time scale of Earth's formation by looking at silicon isotopes from more than 60 meteorites and planetary bodies in the vicinity of Earth, which represent the rubble leftover after planet formation... By analyzing the silicon compositions in samples of different ages, Onyett said they can piece together a time sequence of what was happening in the disk of dust before Earth formed. They found that, as the samples increased in age, the composition of the asteroids changed toward the composition of the cosmic dust that was being accumulated by Earth. "That's very strong evidence that this dust was also being swept up as it was drifting inwards towards the Sun," said Onyett. "It would have been swept up by Earth as it was growing by accretion."

Birger Schmitz, an astrogeologist at Lund University who was not involved in the research, said these results are "very compelling" and could shift how we think about our planet's formation... Most importantly, he said the results show there is nothing special about our water-carrying planet. "It is just a very ordinary planet in our galaxy. This is important in our attempts to understand how common higher forms of life are in the universe."

While scientists agree pebble accretion does explain the formation of gas-giant planets like Jupiter and Saturn, some still argue that rocky planets like Earth were instead formed through larger and larger asteroid collisions...

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