Life developed on earth almost four billion years ago. Despite many catastrophic events, it can hold on its own and evolve. But at some point life will also disappear. So how long is there life left on earth? Let’s find out.
Many catastrophes have done badly on life on earth in the past. Mass extinctions decimated large parts of the animal world. The impact of an asteroid, for example, ended the existence of the dinosaurs. Star explosions and gamma-ray bursts are also said to have had their share. But life never completely disappeared. It always recovered and even became more diverse than before.
The cause is the increasing luminosity of the sun. Inside the sun, helium, a waste product of the fusion of hydrogen that the star uses to generate its energy, accumulates. The helium is denser than hydrogen and increases the pressure and thus the temperatures in the core. This speeds up the fusion process and releases more energy. This hits the earth as radiation and causes temperatures to rise here too.
The CO2 content of the atmosphere decreases
The warming of the earth, in turn, has serious effects on the proportion of carbon dioxide (C02) in its atmosphere. Because the stronger the sun shines, the more C02 is broken down from the air through chemical reactions with rocks. This process acts on a geological time scale of millions of years and in the past has kept global temperatures relatively stable. But it cannot stop the current man-made rise in CO2 in the atmosphere.
Even if too much carbon dioxide in the atmosphere is one of the greatest concerns of mankind today, in the distant future the CO2 content will be too low due to the increasing luminosity of the sun. In about 600 million years, the CO2 concentration in the atmosphere will be below the limit required for photosynthesis. Then plants will no longer survive and the food chains will collapse. Without plants, the oxygen in the atmosphere would no longer be produced and would be used up quickly. Animals would simply suffocate.
But a slightly different process is also conceivable. If the CO2 content remained high enough, multicellular organisms such as mammals and humans would die from heat in 800 million years. The average global surface temperature will then be around 30 degrees Celsius, around twice as high as it is today. It would continue to rise and another 500 million years later, the more complex single-cell organisms would also be affected. In 1.6 billion years, bacteria would no longer be able to survive because of the then definitely too low CO2 content in the atmosphere and the earth would be dead.
Oceans will evaporate
In addition, another effect is likely to affect life. In 1.2 billion years it will be on average 60 degrees warm, which means that a lot of water from the oceans will evaporate and a ‘humid greenhouse’ will be created. High layers of air such as the stratosphere would then also absorb water vapor. There, UV radiation from the sun would split the water into oxygen and hydrogen and the latter would escape into space. The earth will lose its water to space. That would make the surface of the earth completely dry. And without water, life on earth would no longer be possible.
Either way, in just over a billion years, life on earth will cease to exist. However, it was created more than three billion years ago and thus it is in the final quarter of its existence.
Even after all life has disappeared, the luminosity of the sun will continue to increase. In about seven billion years it will probably be more than 2,000 times as bright as it is today and have swelled into a red giant. The temperatures on earth are then likely to be more than 2000 degrees Celsius on average and oceans of lava cover the surface. Later, the sun will lose its cover and begin its retirement as a small white dwarf.