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If you were to imagine all of Earth ’s history as just one day , as in Carl Sagan ’s cosmic calendar , humans would n’t arriveuntil the last few seconds before midnight . A few hundred thousand years of our species come to only a flyspeck fraction of our planet ’s yesteryear . So how old is our planet , and how do we even live its age ?
terra firma take shape about 4.54 billion year ago , about 10 million years after thesolar systemwas born . After a gigantic cloud of gasoline crack up to make the Lord’s Day , snatch of that swarm were left over to make planet .
Earth during hurricane season, as seen by a NASA satellite.
" I like to think of early solar system like a pizza , " saidMark Popinchalk , an astronomer at the American Museum of Natural History and New York University . " If the gas cloud the star forms out of is a ball of cabbage , it might start out like a blob , but it will have some initial spin . The star will constitute out of 99 % of that ' dough , ' but the rest still has that twisting — and , yield enough clock time , it will drop out like a pizza around the superstar . It ’s from that 1 % of the ' dough ' that all the planets are form . "
Baby Earth , however , was nothing like the lush , unripe cosmos we recognize today . Right when it formed , it was still molten from the collision that create it . The heavier bits , like iron , sank to make the core of our planet , and the lighter element bubbled up to the open . finally , this run to a superimposed Earth with acore , mantel and freshness .
Related : How long will Earth subsist ?
Once the solar system calmed down and few asteroids were smacking into Earth , the oceans formed and lifepopped up almost like a shot . " While humans could n’t survive for much of Earth ’s story , cellular life sentence has an continuous streak going for about 3.5 billion geezerhood , " Popinchalk said . ( young research shows that number may even be bigger , as long ago as4.2 billion year ! )
We owe our cognition of this timeline to the literal ground we stand on ; rocks are the key to determining the age of Earth and what it was like in the past . With a appendage experience asradiometric geological dating , scientists can utilize the amounts of unlike radioactive elements to mold how one-time a John Rock is . Earth rocks can be tricky , though , because " Earth is an active , busy place , " Popinchalk order . " Volcanoes , weathering and geologic processes think of that it ’s unmanageable to find rocks from when the Earth formed . "
The moon , however , formed from a collision with our planet in its early childhood , and it does n’t have peskyplate tectonicslike Earth does . Samples ofmoon rocks from the Apollo erahave helped refine our major planet ’s age estimate , andnew samples from missions like Chang’e 5are adding to our apprehension of the Sun Myung Moon ’s chronicle .
— Is Earth getting close to the sun , or farther off ?
— ' Starter ' Earth grew in a flashing . Here ’s how the planet did it .
— How do we acknowledge how old Earth is ?
For nearby planet like Mars , we can send a rover to pick up rocks and dissect them to determine their historic period . But how do we determine the ages of planets around otherstars , which are way too far for us to travel to ?
" The best style to learn about planets around other mavin is actually just to consider the star itself , " Popinchalk articulate . " I specialize in guessing the age of a star by looking at how quickly it is spin out . Young stars spin fast ; older stars spin slow . If I can measure the spin rate of a major planet - host sensation , I can forecast the long time of the star and expend a similar phone number for the satellite . "
As we find out and characterise new world beyond our solar system , we ’re take more about the item of how planet form , which will help us sympathise the history of our own planet even better .
