More than 4.5 billion years ago, the Earth began to form from a mixture of dust and gas that was around our young Sun. Eventually, it grew bigger and bigger until it resembled the planet we live on today, a process that scientists now say happened much faster than they once thought. That formation, they say, also included water, a detail that indicates that finding another habitable planet isn’t out of the question.

In a new study published in Nature this week, researchers say the Earth formed in just 3 million years. This is considerably faster than previous estimates which place the timeline up to 100 million years.

Millions of years may not seem fast to mere humans, but on an astronomical scale, it’s incredibly fast. In the 4.6 billion years of existence of our solar system, 3 million years is like the blink of an eye. That’s the equivalent of less than a minute in a 24-hour day. (If the Earth formed over tens of millions of years, that would equal 5-15 minutes a day.)

Planets can go from their infancy to the size of Earth and Mars in a few million years, which is very fast indeed compared to the hundreds of millions of years previously thought, said Isaac Onyett, lead author of the study and Ph . .D. candidate at the University of Copenhagen. We can also predict that if other planets formed by the same mechanism, then ingredients necessary for life such as water, should be present on other planets and other systems, so there is a greater possibility that we have water worlds elsewhere in the galaxy. .

The authors say 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 quickly pull in those pebbles like a vacuum cleaner. Some of those pebbles are frozen and could provide a water supply to the Earth, thought of as pebble snow. This would have led to an early version of our planet, known as proto-Earth, which is about half the size of our current planet. (Our current representation of Earth likely formed after a major impact about 100 million years later, which also resulted in the formation of our moon.)

However, this pebble accretion theory for Earth formation is controversial.

Scientists agree that this theory explains the formation of gas giants in our solar system, such as Jupiter and Saturn, pebble accretion is the only way for a giant planet to grow fast enough before its planetary disk dissolves . But it is disputed for their terrestrial counterparts. Others have pointed out issues about where the pebbles come from around planet Earth or why the planets aren’t bigger.

A more traditionally accepted theory is that terrestrial planets, like Earth, formed through a sequence of asteroid collisions that got progressively larger and larger, Onyett said. This process would mean that the Earth took about 100 million years or more to form. In this mechanism, the presence of water on Earth may have been fortunate, perhaps delivered by an asteroid or comet.

Co-author Martin Schiller said he and his colleagues want others to rethink how terrestrial planets form. Yes of course, pebbles are available everywhere. Naturally, terrestrial planets will also grow by accretion of pebbles, said Schiller, also a cosmochemist at the University of Copenhagen.

Bizzarro added that this study provides the strongest evidence that terrestrial planets formed through pebble accretion.

The team determined the timescale of Earth’s formation by observing the silicon isotopes of more than 60 meteorites and planetary bodies in the Earth’s vicinity, which represent the debris left over after the planet’s formation. Silicon is a major element in rocks and a vital building block of a planet, similar to what carbon is to life. Because it is so abundant in the universe, it is easily and commonly produced and can serve as a good tracer for planetary formations.

By analyzing silicon compositions in samples of different ages, Onyett said he could piece together a timeline of what was happening in the dust disk before Earth formed. They found that as the samples increased in age, the composition of the asteroids changed towards the composition of cosmic dust that was being accumulated by Earth.

This is very strong evidence that this dust was also blown away as it moved inward towards the Sun, Onyett said. It would have been swept off the Earth as it grew by accretion.

Birger Schmitz, an astrogeologist at Lund University who was not involved in the research, said these findings are very compelling and could change the way we think about the formation of our planets.

If these interpretations hold (and I think they will), it represents a major paradigm shift in our understanding of Earth’s formation, Schmitz, a research associate at the Chicago Field Museum, wrote in an email. Paradigm shifts always come as big surprises… wrong have we been for so long!

More importantly, he said the findings show there’s nothing special about our planet that carries water. It’s 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.

Cosmo isotope chemist Francois Tissot, who was not involved in the study, said the new research presented a fascinating insight into the isotopic composition of silicon in so many planetary materials. But he’s not sure that pebble accretion is the simplest explanation for trends in the silicon data. He said further analysis of how the new isotope data fits, or doesn’t fit, with other models is needed.

Still, these are exciting results that will bring key new constraints to our understanding of Earth’s formation, said Tissot, based at the California Institute of Technology. It’s an exciting time for the community and an undeniable step forward.

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