Earth sustains life only because our planet teeters on a delicate and truly improbable balance.
Our atmosphere, proximity to the sun, and countless other beautiful coincidences not only permit life to evolve but also thrive.
And yet, here we are, sitting at desks and in coffee shops and walking down the street like our very existence isn't some kind of extraordinary miracle.
But all good things must come to an end.
One day Earth will be inhospitable to anything resembling life as we know it.
The life on this planet likely won't until billions of years from now. But, depending on the vicissitudes of astrophysics, it could also happen tomorrow or anytime in between.
Here are the many ways scientists believe the Earth could die.
1) The Earth's molten core might cool.
Earth is surrounded by a protective magnetic shield, called the magnetosphere.
The field is generated by Earth's rotation, which swirls a thick shell of liquid iron and nickel (the outer core) around a solid ball of metal (the inner core), creating a giant electric dynamo.
The magnetosphere deflects energetic particles that emanate from the sun, changing its size and shape as it's hit.
Source: National Oceanic and Atmospheric Administration (NOAA)
If the core cools, though, we'd lose our magnetosphere — and also our protection from solar winds, which would slowly blast our atmosphere into space.
Source: Live Science, Tech Insider
Mars — once rich with water and a thick atmosphere — suffered this same fate billions of years ago, leading to the seemingly lifeless world we know today.
Source: Tech Insider
2) The sun could start to die and expand.
The sun, and our position relative to it, is perhaps the most important piece of our tenuous existence.
But the sun is still a star. And stars die.
Right now, the sun is midway through life, steadily converting hydrogen into helium through fusion.
That won't last forever, though. Billions of years from now the sun will run low on hydrogen and start fusing helium.
Source: The Conversation
It's a more energetic reaction and will push the sun's layers outward, and possibly start pulling the Earth toward the sun.
Sources: Cornell, Scientific American
We'd be incinerated and then vaporized.
Sources: Scientific American
That or the sun's expansion would push the Earth out of orbit. It'd die frozen as a rogue planet, untethered to any star and drifting through the void.
Source: The Conversation
3) We could collide with a rogue planet. Speaking of rogue planets, space isn't kind. Planets often get kicked out of their solar systems during formation.
Source: National Geographic
According to recent simulations, in fact, rogue planets may outnumber stars in the Milky Way by 100,000 to one.
Source: National Geographic
One of those rogue planets could drift into the solar system, put Earth into an extreme and inhospitable orbit, or even kick us out of the solar system.
Source: University of Cambridge
Or one could crash into Earth and obliterate it. It wouldn't be unprecedented. About 4.5 billion years ago, a small planet crashed into a larger planet in the solar system — forming Earth and its moon.
Source: NASA
4) Asteroids could bombard the planet. Hollywood loves death-by-asteroid.
Rocks from space can be pretty destructive — a big one probably wiped out the dinosaurs — though it would take a lot of asteroids to properly dispatch the entire planet.
Still, it could happen. Earth was heavily bombarded by asteroids for hundreds of millions of years after it formed. The impacts were so intense that the oceans boiled for a full year. All life was single-celled at that point, and only the most heat-tolerant microbes made it. Today's larger lifeforms almost certainly wouldn't make it. Air temperatures could reach more than 900 degrees Fahrenheit for several weeks if we suffered a similar pummeling.
Source: Wired, New Scientist, Science News
5) The Earth could pass too close to a wandering black hole.
Black holes might be Hollywood's second-favourite form of planet death. It's easy to see why.
They're as mysterious as they are frightening. Even the name is ominous.
Source: NPR
We don't know much about them, but we do know they're so dense that not even light can escape beyond a black hole's event horizon.
And scientists think "recoiled" black holes are out there wandering through space. It's not inconceivable that one could pass through the solar system.
Source: NASA
If light can't escape, the Earth definitely won't. There are two ideas about what could happen after the point of no return, given a big-enough rogue black hole. (A smaller one would just spaghettify the planet.)
Source: KIPAC/Stanford
Beyond the event horizon, atoms might stretch until they're pulled apart entirely.
Source: Business Insider
Other physicists have theorized we'd run right into the end of the universe, or end up in an entirely different one.
Source: National Geographic
Even if a recoiled black hole misses Earth, it might pass closely enough to cause earthquakes and other devastation, kick us out of the solar system, or spiral us into the sun.
Source: AskAMathematician
6) The Earth could be obliterated in a gamma ray burst.
European Space Organization via Wikimedia Commons (CC BY 3.0)
Gamma ray bursts, or GRBs, are one of the most powerful phenomena in the universe.
Source: Universe Today
Most are the result of massive stars collapsing when they die. One short blast can emit more energy than our sun will over the course of its lifetime.
Source: National Geographic
That energy has the potential to eradicate the ozone layer, flood the Earth with dangerous ultraviolet light, and trigger rapid global cooling.
Source: International Journal of Astrobiology
In fact, a GRB pointed at Earth might have caused the first mass extinction 440 million years ago.
Source: Live Science
Luckily, David Thompson, deputy project director on the Fermi Gamma-ray Space Telescope, told National Geographic that GRBs aren't really a big concern.
He told the magazine the risk was equivalent to "the danger I might face if I found a polar bear in my closet in Bowie, Maryland."
Source: National Geographic
7) The universe could go to pieces in its final "Big Rip."
This is the thing that could actually end the whole universe, not just the Earth.
The idea: A mysterious force called dark energy is pushing the universe apart at a faster and faster rate.
If this keeps accelerating, as it seems to be doing now, perhaps 22 billion years from now the force that keeps atoms together will fail — and all matter in the universe will dissolve into radiation.
But assuming the "Big Rip" is a dud, who knows what might happen after a global calamity humans don't survive?
It's possible some microbes will survive to reseed life.
But if our destruction is total, we could at least hope some other intelligent life exists out there, and can pay its respects.
Kelly Dickerson contributed to this post.
Read the original article on Business Insider. Follow us on Facebook and Twitter. Copyright 2018.
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