All good things, they say, must come to an end – and like woolly mammoths, Tasmanian tigers, and the CW’s Supernatural, one day, humanity’s time will run out for good.
In fact, much as we hate to think about it, eventually, everything on Earth will end. But when will that be? Well, believe it or not, we have some weirdly specific dates on that.
When will Earth become uninhabitable?
As you may be aware, humans are sort of turning the planet into a fiery hellscape wracked by constant climate disaster. As you may not be so aware, we’re also taking everything else with us.
“It’s not just the number of species that is declining,” said François Keck, a postdoctoral researcher in Altermatt’s research group and the lead author of a massive synthesis study measuring the extent and impact of human activity on the natural world, earlier this year. “Human pressure is also changing the composition of species communities.”
It’s a worrying picture on multiple levels: species are dying off; biodiversity is being lost; ecological niches are no longer being fulfilled. Even without human intervention, we’re already at the point where animals – including our own species – are dropping dead from extreme heat and resource loss, to say nothing of the increasingly dramatic and unpredictable climate events that are turning up more and more these days.
But let’s be optimists. Let’s say we live in a magical alternative universe where the world’s governments see the oncoming disaster and actually take action to avert it, saving us all.
Well, sorry, but we’re still heading for that hell world – it’ll just take a whole lot longer to arrive.
“The outlook in the distant future appears very bleak,” said Alexander Farnsworth, Senior Research Associate with the Cabot Institute for the Environment at the University of Bristol, in 2023. As lead author on a study using supercomputers to model global climates over the next 250 million years, Farnsworth and his team discovered a picture of an Earth virtually uninhabitable by any mammal.
At the end of that quarter-billion years, “carbon dioxide levels could be double current levels,” he explained. “With the Sun also anticipated to emit about 2.5 [percent] more radiation and the supercontinent being located primarily in the hot, humid tropics, much of the planet could be facing temperatures of between 40 to 70 °C [104 to 158 °F].”
That world will be one we don’t recognize – dominated by a single supercontinent; the atmosphere containing some 50 percent more CO2 than current levels, with a Sun hotter and brighter than it now is. “Widespread temperatures of between 40 to 50 degrees Celsius [104 to 122 °F], and even greater daily extremes, compounded by high levels of humidity would ultimately seal our fate,” Farnsworth said.
When will Earth run out of oxygen?
It’s a bleak picture for us, but not necessarily for everybody. After all, life can survive even in the Atacama desert – so why would a little thing like super-solar-radiation and constant sauna-level temperatures wipe everything out entirely?
No, for a more dramatic doomsday scenario, we need to widen our perspective a little. Make life not just uncomfortable, but impossible. Take away the oxygen.
“For many years, the lifespan of Earth’s biosphere has been discussed based on scientific knowledge about the steadily brightening of the sun and global carbonate-silicate geochemical cycle,” explained Kazumi Ozaki, Assistant Professor at Toho University, in a statement in 2021.
But that discussion is missing something, he said. “One of the corollaries of such a theoretical framework is a continuous decline in atmospheric CO2 levels and global warming on geological timescales,” Ozaki continued. “Indeed, it is generally thought that Earth’s biosphere will come to an end in the next 2 billion years due to the combination of overheating and CO2 scarcity for photosynthesis.”
If that sounds like a gloomy prediction, take heart: Ozaki, along with co-author Christopher Reinhard, an Associate Professor at the Georgia Institute of Technology, calculated that the time limit for life on Earth is probably much shorter than that. Using computer models to stochastically forecast climate and biogeological processes, the pair concluded that Earth’s oxygen-rich atmosphere will likely only last another billion years or so.
Unfortunately, there’s truly nothing we can do about it. “Future deoxygenation is an inevitable consequence of increasing solar fluxes,” the pair wrote in a Nature-published study, while “its precise timing is modulated by the exchange flux of reducing power between the mantle and the ocean-atmosphere-crust system.”
Basically, as the Sun grows more luminous – a natural consequence of its ageing – the CO2 in the atmosphere will get stripped away. Sounds like a good thing to greenhouse-gassed humans, maybe – but if you’re a plant, it’s a recipe for starvation.
With no plants photosynthesizing, there’s simply no oxygen being produced. “The [forecast] drop in oxygen is very, very extreme – we’re talking around a million times less oxygen than there is today,” Reinhard told New Scientist at the time.
The result: a world similar to the one that existed around 2.5 billion years ago – before the so-called “Great Oxidation Event” that kickstarted life as we know it. The atmosphere will be “characterized by […] elevated methane, low levels of CO2, and no ozone layer,” Ozaki said.
It will happen very quickly – over the course of just 10,000 years or so – and it will be devastating. “The biosphere cannot adapt to such a dramatic shift in environmental change,” Ozaki told New Scientist.
And the worst news of all? That’s kind of a best-case scenario.
“Some models predict that terrestrial C3 plants will cease to be viable at Earth’s surface less than ~500 [million years] into Earth’s future,” the pair wrote. “If true, this might place a long-term physical limit on the ability of photosynthetic biospheres to maintain high levels of atmospheric oxygen, giving rise to a fundamental trade-off between long-term stellar evolution, the geologic carbon cycle and the intrinsic timescale of atmospheric oxygenation.”
The end of all life on Earth?
So: two billion years, and all life will be gone. Right?
Well, possibly not. It’s not for nothing that the “Great Oxidation Event” is also known as the “Oxygen Holocaust”; while rising oxygen levels were a boon for the development of complex life, it was terrible for the organisms that were already around.
And there were organisms around: tiny, anerobic life forms, surviving by using retinol to extract energy from green-spectrum light. It’s not going to produce the Mona Lisa or write any symphonies, but it’s something – and after the great deoxygenation, “many of the anaerobic and primitive bacteria [that] are currently hiding in the shadows will, again, take over,” Reinhard told New Scientist.
The definitive point at which life can no longer exist on Earth, then, will likely be when the Sun explodes, becoming a red giant big enough to gobble up its nearest planets – including us. Technically, the Earth will be just 42 “years” old at that point – though for a human timescale, we can think of it as around five to seven billion years from now.
Until then – well, to quote a great mathematician: life, uh, finds a way.
Source Link: When Will All Life On Earth Die Out? Here's What The Data Says
