Asteroid impacts, supernova explosions, and other calamities could wipe out humanity. But no matter what, a catastrophic event a billion years from now will likely rob the planet of oxygen and wipe out life.
Life is resilient. EITHERfirst living things on earthIt appeared 4 billion years ago, according to some scientists. At the time, our planet was still being pummeled by huge space rocks. But life persisted anyway. And throughout Earth's history, we've seen all kinds of cataclysms. Disparate apocalypses, from supernova and asteroid explosions to massive volcanic eruptions and sudden climate changes, have killed countless forms of life. And sometimes these mass extinctions even wiped out most species on Earth.
However, life has always recovered. New species emerge. The cycle repeats itself.
So what would it take to kill life completely? Well, it turns out that while humanity can be surprisingly fragile, it's not easy to sterilize an entire planet. However, below are just a few possible apocalyptic events that could permanently extinguish all life on Earth, with the last one likely inevitable.
This artist's illustration highlights the tremendous amount of energy released when an asteroid hits a planet.
asteroid impact apocalypse
When oneCity-sized asteroid hit the Gulf of Mexico 66 million years ago, it was game over for dinosaurs, as well as most other species on Earth at the time. And while our ancestors hadn't yet evolved, the impact was perhaps the most important event in human history. Without the asteroid impact, dinosaurs might have continued to rule Earth, leaving us mammals still cowering in the shadows.
Humans, however, will not always be on the winning side of these random events. A future asteroid could easily destroy all people on Earth. Fortunately, that's unlikely to happen anytime soon. According to the geological record of cosmic impacts, the Earth is struck by a large asteroid approximately every 100 million years.according to nasa. However, smaller asteroid impacts happen all the time. There is even evidence that some people may have beenkilled by small meteorite impactsduring the last thousands of years.
But what are the chances that our planet will be hit by an asteroid big enough to wipe out all life on Earth? Simulations published inNaturein 2017they suggest that it would take a truly gigantic space rock to accomplish such a feat. Killing all life on Earth would require an impact that would literally evaporate the oceans. And only asteroids like Pallas and Vesta, the largest in the solar system, are big enough to do that. There is evidence thatInfant Earth was struck by a large planetoid called Theia. But today, collisions of such large objects are extremely unlikely.
A fossil of a trilobite, one of the first arthropods on Earth, is seen on display at the Shanghai Museum of Natural History. Trilobites ruled the world during the Ordovician.
death by deoxygenation
To get a more likely view of an Earth-altering cataclysm, we must look into the distant past.
Almost 2.5 billion years ago, a period calledGreat oxidation eventit gave us the breathable atmosphere we all now depend on. An eruption of cyanobacteria, sometimes called blue-green algae, filled our atmosphere with oxygen, creating a world where multicellular life forms could take root and where creatures like humans could finally breathe.
However, one of Earth's great deaths, an event from 450 million years ago called the Late Ordovician mass extinction, probably happened because the opposite happened. The planet saw a sudden drop in oxygen levels that lasted for several million years.
What could have caused such an extreme event? During the Ordovician period, the continents were a messy mass called Gondwana. Most of the life on Earth still lived in the oceans, but plants were beginning to emerge on land. Then, near the end of the Ordovician, radical climate change left the supercontinent covered in glaciers. That global cooling alone was enough to start killing off species.
But then a second extinction pulse kicked in as oxygen levels plummeted. Scientists see evidence of this change in deep-sea samples collected from around the world. Some researchers believe that glaciers were responsible for fundamentally altering the layers of the oceans, which have unique temperatures and specific concentrations of elements such as oxygen. However, the exact cause of the oxygen drop is still up for debate.
Whatever the cause, the end result is that more than 80% of life on Earth went extinct during the Late Ordovician mass extinction.according to some estimates.
So it may have happened before, but can a deoxygenation event happen again? In an uncanny comparison to today, the researchers involved in the recentnature communicationsClimate change is already reducing oxygen levels in our oceans, which could kill marine species, a study says.
Bright beams of light called gamma-ray bursts can originate in binary star systems, as shown in this illustration.
Universidad de Warwick/Mark Garlick
gamma ray burst extinction
Even if a sudden wave of global cooling triggered the late Ordovician mass extinction, what triggered it in the first place? Over the years, numerous astronomers have suggestedthe culprit may have been a gamma-ray burst(GRB).
GRBs are mysterious events that appear to be the most violent and energetic explosions in the cosmos, and astronomers suspect they are related to extreme supernovae. However (and thankfully), we still haven't seen an explosion close enough to us to fully understand what's going on. Until now, GRBs have only been seen in other galaxies.
But if one were to occur in the Milky Way, as it probably did in the past, it could cause a mass extinction on Earth. A GRB pointed our way might only last 10 seconds or so, but it could still destroy at least half of Earth's ozone in that short period of time. As humans have learned in recent decades, even a relatively large populationsmall amount of ozone depletionit's enough to destroy our planet's natural sunscreen, causing serious problems. Large-scale ozone depletion could wreak havoc on food chains, killing large numbers of species.
A GRB would eliminate life forms living in the upper levels of the ocean, which currently contribute significant amounts of oxygen to our atmosphere. And it turns out that gamma rays also break down atmospheric oxygen and nitrogen. These gases are converted to nitrogen dioxide, which is more commonly known as sun-blocking smog over heavily polluted cities. Having this pollution covering the entire Earth would block out sunlight and usher in a global ice age.
Eventually, the emissions from the aging Sun will be so intense that they will deplete the oxygen in Earth's atmosphere.
end of the sun
Any of the above devastating scenarios, while undoubtedly dire for life, is only a fraction as bad as the ultimate fate of the future Earth. Gamma-ray burst or not, in about a billion years, most life on Earth will eventually die out anyway due to lack of oxygen. That's according to a different study published in March in the journalNaturegeoscience.
The researchers suggest that our oxygen-rich atmosphere is not a permanent feature of the planet. Instead, in around a billion years, solar activity will bring atmospheric oxygen back to the level it was before the Great Oxidation Event. To determine this, the authors combined climate models and biogeochemical models to simulate what will happen to the atmosphere as the Sun ages and releases more energy.
They found that eventually the Earth reaches a point where atmospheric carbon dioxide breaks down. At that time, oxygen-producing plants and organisms that depend on photosynthesis will die. Our planet will not have enough life forms to sustain the oxygen-rich atmosphere that humans and other animals need.
Exactly when this starts and how long it takes (the deoxygenation process could take as little as 10,000 years) depends on a wide range of factors. But in the end, the authors say that this cataclysm is inevitable for the planet.
Fortunately, humanity still has another billion years to figure out other plans.