If the sun suddenly disappeared, how long would life on Earth last, from humans and plants to subterranean bacteria?
Anthony Woodward
Portland, Oregon, US
It depends what is meant by “disappeared”. If it means the sun and its mass being deleted by some god-like entity, then 8 minutes later, Earth would stop orbiting and move off in a straight line towards the boundary of the solar system at 107,000 kilometres per hour. So would the other planets. Eventually, Earth could catch up with Jupiter moving at about 47,000 km/h. Earth might even become another moon of Jupiter, now the most massive body in the solar system. All life would have frozen to death before we reached the hazards of the asteroid belt.
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If “disappeared” means we no longer see the sun because the sun has stopped emitting light and heat (but its mass remains), then 8 minutes later, photosynthesis stops. But there would be little immediate change. After all, life on Earth is accustomed to the dark of night.
The surface of Earth would cool rapidly. Within a week, surface water would be frozen and most plants and animals would begin to die. Any water deep below the ice would remain liquid for decades, so some aquatic animals could live for years feeding on detritus.
If the sun disappeared, Earth would simultaneously be obliterated by the cataclysmic event that caused it to disappear
Less than 0.001 per cent of life on Earth doesn’t depend on photosynthesis. Such organisms, typically found in the depths of the oceans, could survive until even those depths froze.
But humans are inventive, with access to huge amounts of energy in the form of fossil fuels and nuclear power. Our cities shine so brightly they are visible from space. We would light and heat our homes. We could create vast greenhouses to grow the plants we like to eat, and even enough grass to feed cattle for meat and milk. Of course, such use of energy requires the money and political control of wealthy people. Those who can’t afford it would starve.
Hillary Shaw
Newport, Shropshire, UK
If humans aren’t around, temperatures fall below freezing everywhere within a week and all bodies of water ice over. Plants are dormant, later to die when their cells freeze, and land animals die of thirst if the cold hasn’t claimed them.
Within a year, all water bodies except deep oceans have frozen solid, killing all life in them. After two years, atmospheric nitrogen will rain out (which condenses at -196°C), as will the oxygen (-183°C). All surface land life and soil bacteria are now dead. Life clings on in deeper oceans, which take 1000 years to freeze almost solid, although most higher oceanic life has starved by then. The last survivors are tubeworms at oceanic vents, where the ocean may not ever totally freeze as Earth’s geothermal heat continues for millions of years.
But if there is no liquid water to lubricate plate tectonics, Earth’s plate system may partially seize up. This causes less frequent, but catastrophic earthquakes and volcanic eruptions. Maybe some deep sea vent life won’t survive this.
With humans, given a year’s warning, we might construct underground shelters for billions. We would need geothermal power at an unprecedented scale, and intensive farming, maybe “vertical farms”. Many people in low-income countries would still be unable to secure a place, unless they mounted a mass invasion of higher-income countries. Then most humans would die in the total world war that ensues, and most shelters wouldn’t get built. Psychological issues would be numerous, from lack of access to nature to the need for strict totalitarian control.
On the day the sun goes out, we buy some time by quickly burning the forests, which will die anyway, creating a massive greenhouse effect. Maybe then, after a year, average global temperature is a balmy 0°C and the oceans may not have frozen. We then need to give the population hope and a purpose, so we build a huge “Noah’s Ark” spaceship. This will take as many different life forms as possible with less than 1 billion humans on a long voyage with no clear destination, just a desperate search for another suitable planet, knowing many generations will pass on board before we find one.
Andrew Ward
Wotton-under-Edge, Gloucestershire, UK
If the sun suddenly disappeared, Earth would simultaneously be obliterated by whatever cataclysmic event caused it to disappear. Possibly delayed by 8 minutes.
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