There is no doubt that, at one time or another, life on our planet will come to an end. It will not be something that arrives suddenly and without warning, unless a meteorite of those called the Final Judgment collides with the Earth. All scientific models point to an end times with rising temperatures , continued disappearance of various forms of life and evaporation of the oceans. And the day will come when the last survivor of all living organisms will die. We even know what it will be like: a unicellular being, very similar to the first forms of life that appeared on the planet. But many things will have happened before.
In a few tens of thousands of years we will find ourselves before a white planet, where snow will cover from the poles to the Mountains of the Moon in Africa . The level of the sea, whose rise is so worrying today, will fall, revealing new coastlines, uniting islands with continents and turning gulfs into prairies. Survivors of a defunct civilization will not need to use the Channel Tunnel; They can walk to Dover… if they can stand the cold. The few humans alive are likely to huddle around campfires in equatorial zones. We will be in the next Ice Age, worse than the one endured by Cro-Magnons and Neanderthals.
The age of fossil fuels will be a mere legendary memory, like when the planet was much warmer. Humanity, who flourished during a brief interglacial period, will feel on their own skin the true nature of the planet, the same that has been felt for the last 3 million years: the reign of ice. Humans will live in a colder and, paradoxically, drier world . The forests and jungles will have disappeared, becoming savannahs, the granaries of the world will be dry lands and the winds will blow fiercely at 200 kilometers per hour, whistling through the plains that the ice will have inexorably covered. Little will remain of what was once the presumptuous civilization that believed to dominate the planet: not even its proud skyscrapers will remain standing, demolished by columns of ice half a kilometer high. Survival will be more and more complicated; will have to fight too much to feed. Our descendants will be starving .
After humanity has disappeared
But the disappearance of humanity will not imply the annihilation of life. Millions of years after the final death rattle of the last human being is lost in the atmosphere, life will continue its course towards its end. In groundbreaking work from 1982, James Lovelock and Mike Whitfield pointed out that a deficit of carbon dioxide in the atmosphere is disastrous. Taking into account that the Sun is getting brighter, they calculated that plants will die within 100 million years because carbon dioxide levels will have fallen below 150 parts per million, almost three times less than today. . Since then, various scientists have improved the Lovelock-Whitfield model, delaying the last day of life on Earth by 500 million years .
For his part, Christopher Scotese, from the University of Texas at Arlington, has calculated that within 250 million years all the continental masses will reunite in a single supercontinent, Pangea Ultima . Life then will not be easy. In tropical latitudes the temperature will be high, around 40º C, while in intermediate latitudes the hot summers will be followed by very cold winters , with heavy snowfall and temperatures of 20 and 30º below zero. The alluvium caused by the spring thaw will be impressive. Despite this, the vast interior will be dry as the rain clouds will barely reach inland.
Meanwhile, in the sky the Sun will shine with more intensity. Our star becomes 1% brighter every 100 million years, causing a continuous increase in temperature, which will decrease its carbon dioxide content. According to scientists James Kasting and Ken Caldeira, in 500 million years carbon dioxide levels will have fallen by 40%, photosynthesis will have practically disappeared and 95% of plant species will be on the verge of extinction. Only cacti and shrubs will be able to survive in these conditions. In 900 million years there will not be enough carbon dioxide even for them. In an atmosphere with oxygen on the verge of disappearing forever, the planet will be changing from green to brown.
From half a million years…
For their part, in 500 million years the animals that still exist will have to face the lack of nutrients and heat. When the global temperature of the planet exceeds 38º they will begin to die at the equator and the animals will migrate towards the poles. Above 40º on average, either new species capable of withstanding such heat have appeared or animal life will face extinction: above 45º degrees, cell mitochondria stop working. Life, cornered near the poles, must be nocturnal, hiding from the dangerous Sun. As the temperature rises, animal life will subsist by burrowing. Only bacteria can be found on the surface. When the average 50º is reached, the extinction will be practically total on land. Life in the sea will last a little longer.
In 1.2 billion years the sun will be 15% brighter, which will cause the surface temperature to reach 70º C on average and practically all the carbon dioxide will have disappeared from the atmosphere . The global circulation system of the oceans will have stopped, so the planetary thermostat will be off. In the sea there will be no fish; we will be facing a dead sea, except for the blue-green algae. They were the first and will be the last in the history of life. The color of the sea will have changed to brown due to the large amount of sediment carried by the waters and dust storms.
The mountains will slowly erode due to the winds and the few remaining streams, half buried by their own gravel. Imagining the deltas of the Ebro, the Nile or the Amazon crossed by trickles of water is a good image of that distant future. Ultraviolet radiation from an increasingly bright Sun will break down the water molecule . The Earth’s gravity will not be able to prevent the hydrogen from escaping into space, while the oxygen will be absorbed by the metallic rocks, subjected to a pressure of hundreds of atmospheres. Earth will have become a rusty planet, like Mars today. The atmosphere will be more like that of Venus , with clouds of sulfuric acid. Perhaps the temperature reaches 1,000º C, enough to turn most of the rocky surface into rivers or seas of magma. In this way the Earth will face its irremediable end.
Reference:
Ward, P.; Brownlee, D. (2004) The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of Our World, Holt
