The extinction of humanity
Life on Earth will surely be wiped out eventually. Humans face pressure from a changing planet with limited resources, from other humans and from the natural world. Whether an out-of-this-world catastrophe, like an asteroid strike, occurs or not, the demise of humanity is inevitable. All things must pass. That includes life on Earth, which will surely be wiped out eventually. But how long does it have?
The fossil record tells us that life on Earth has lasted at least 3.5 billion years. In that time it has survived being frozen, clobbered by rocks from space, mass poisoning, and even lethal radiation.
But there’s no shortage of potential apocalypses. Which of them will finally render the Earth barren?
The boiling of Earth’s oceans.
For billions of years, Earth has been an ocean-covered world, with simple and complex life originating in the seas and only coming onto land relatively recently. Yet thanks to the future evolution of our Sun, our oceans won’t be around forever. Over time, the Sun heats up and expands, becoming more luminous and emitting more power as time goes on. As the oceans boil and the atmosphere fills with water vapor, the greenhouse gas effects will take over, causing Earth’s temperature to rise catastrophically.
Volcanic apocalypse (within 100 million years)
The life has come to ultimate destruction on our planet 250 million years ago during the Permian mass extinction. The event obliterated perhaps 85% of all land species and 95% of all ocean-dwelling species.
Asteroid threat (within 450 million years)
It’s common knowledge these days that asteroids and dinosaurs don’t get along. If a massive asteroid could contribute to the extinction of all of the world’s large dinosaurs, could one also wipe out all life on Earth? Objects more than a half-mile wide—which strike Earth every 250,000 years or so—would cause firestorms followed by global cooling from dust.
Reversal of Earth’s magnetic field (3 to 4 billion years)
Worse, the strength of our magnetic field has decreased about 5 percent in the past century. The magnetic field deflects particle storms and cosmic rays from the sun, as well as even more energetic subatomic particles from deep space. Without a magnetic field our planet will lose its atmosphere, and all life will die.
Another life destroyer are intense waves of radiation called gamma-ray bursts (GRBs). They are formed by intense explosions in space, for instance when a giant star explodes or two stars collide. A long GRB could obliterate Earth’s ozone layer, leaving the life on the surface exposed to deadly ultraviolet radiation from the Sun.
For billions of years, the planets of our solar system have been performers in a stately dance around the sun. But what would happen if another star came barrelling through?
Expanding Sun (between 1 and 7.5 billion years)
Our home star bathes us in light, and supplies the energy for almost all the life on Earth. But it won’t be friendly forever.
As we saw earlier, the Sun is gradually getting hotter. Eventually it will be hot enough to evaporate all Earth’s oceans, and cause a runaway greenhouse effect that sends temperatures soaring upwards. This process might begin in about a billion years, and would wipe out all but the most resistant microorganisms.
Germs and people have always coexisted, but occasionally the balance gets out of whack. The Black Plague killed one European in four during the 14th century; influenza took at least 20 million lives between 1918 and 1919; the AIDS epidemic has produced a similar death toll and is still going strong.
The death of Milky Way
On Earth, we’ve got another billion years or two before the oceans boil and the planet becomes uninhabitable. The Sun will heat up, swell into a red giant, fuse helium in its core, then blow off its outer layers and contract into a white dwarf. But even our own Milky Way will cease to exist. When enough time passes, there will be no stars, stellar remnants, or even black holes left at all.
Sources: BBC “Earth”, Discover, Forbes