New theory of Earth's rapid creation makes alien life more likely
(The Hill) – The formation of the Earth may have looked more like a fast, inevitable landslide than like a slow series of occasional cataclysms, as scientists have long theorized, according to findings published on Wednesday in Nature.
If it did, Earth-like planets could be far more common than previously thought, the findings suggest.
The paper represents a groundbreaking revision of the conventional understanding of how the Earth was created — and a new theory about the origin of the planet’s life-giving water.
The appearance of that water, its authors wrote, “might not have happened entirely by chance.”
That would represent very good news for the search for Earth-like planets — not to mention alien life.
The findings put forward a radically revised model of how planets like ours — small, rocky and wet — tend to form across the galaxy, under which a very different vision of life in the universe emerges.
“With this new planet formation mechanism, the chance of having habitable planets in the galaxy is much higher than we previously thought,” said coauthor Martin Bizzarro of Denmark’s Globe Institute.
Wednesday’s study revises two pieces of conventional understanding, which can be reduced to a single idea: that the Earth is the way it is because of a long history of titanic collisions between celestial objects.
In the conventional account, the Earth — and all rocky planets — formed from the infrequent but cataclysmic series of “giant impacts” between embryonic proto-planets.
Because these are very uncommon occurrences, even in the crowded terrain of the early solar system, that would mean that it took a very long time for Earth to form: a period of more than a hundred million years, approximately the amount of time that separates us from the emergence of Tyrannosaurus Rex.
“If that is how Earth was formed, then it is pretty lucky that we have water on Earth,” said study coauthor Martin Schiller, also of the Globe Institute.
That’s because in the long-term, repeated-smashing model of Earth’s creation, any water on those colliding planetoids would be destroyed — so “the presence of water on Earth would need a sort of chance event,” Schiller added.
Specifically, the current presence of water would require an unlikely series of large-scale collisions — in this case, between water-bearing comets or asteroids and the smoldering infant Earth.
By extension, “this makes the chances that there is water on planets outside our Solar System very low,” Schiller said.
But by comparing rocky samples from Earth and Mars with a survey of dozens of meteorites from the early years of the solar system, the Nature team found evidence for an alternate model: one in which the Earth formed by the equivalent of a sudden rockslide.
To get a glimpse of what this might have looked like, let’s travel back 4.5 billion years to the early days after the formation of the solar system.
During this period, the Sun drifted alone amid an orbiting cloud of celestial dust left over from the ruins of a previous supernova — similar to the dust which had gradually fused in earlier ages to make the Sun itself.
That dust contained millimeter-sized pebbles covered in tiny ice particles — pebbles which began to fall into each other, forming a clump that grew faster and faster as its growing gravity allowed it to draw in ever more dust. Eventually, those clumps reached the status of planets.
“Once a planet reaches a certain size, it sorts of act like a vacuum cleaner, sucking up all that dust very quickly,” first author Isaac Onyett said in a statement.
In such a dynamic, a planet the size of the Earth can form in less than 5 million years — still a very long time, but more than 20 times faster than in the conventional understanding. For comparison, 5 million years is the approximate amount of time that separates contemporary society from the first proto-hominids to walk on two legs.
Such a process also allows water to accrete gradually onto a growing planet throughout its formation — rather than in a lucky strike long after the process has ended.
Such a finding would indicate that Earth’s temperate, habitable state is less a freak chance than a natural consequence of its orbital position in the size of our Sun.
“This theory would predict that whenever you form a planet like Earth, you will have water on it,” Bizarro said.
“If you go to another planetary system where there is a planet orbiting a star the size of the Sun, then the planet should have water if it is in the right distance,” he added.