Humanity alone has proven just how fragile our planet is and the profound effect that we have on the Earth’s biosphere will no doubt continue to play an important part of its evolution. It is, therefore, also quite likely that Earth’s natural fate will be overshadowed much sooner by our own tendency towards destruction. Nonetheless, Earth’s ultimate fate ultimately lies with that of the natural evolution of the Sun. Humanity will be long gone before life on Earth comes to its natural end and every trace of our brief existence in the Universe will have vanished except, perhaps, for the lonely space probes floating eternally through the voids of the cosmos.
Photosynthesis Becomes Impossible, 600 Million Years
As part of its natural evolution just like that of any other main sequence star, the Sun is constantly getting hotter, larger and more luminous. In around 600 million years’ time, the expanding Sun will start to have a major effect on Earth’s geology. The Earth will gradually become a geologically dead world as plate tectonics stop and carbon dioxide levels begin to drop. At the same time, the oceans will start evaporating and photosynthesis, which almost all of the world’s species rely on either directly or indirectly, will become impossible. Almost all life will cease to exist.
A Humid Greenhouse World, 1 Billion Years
In around one billion years’ time, the Sun will be about 10% more luminous than it is now and the average surface temperature of the Earth will become about 47 degrees centigrade compared to 15 degrees today. At this point, the atmosphere will have a major greenhouse effect and what is left of the oceans and other bodies of water on the surface will disappear entirely. There may, however, remain some smaller bodies of water around the poles for a little longer, perhaps still inhabited by basic forms of life.
A Completely Dead World, 2.8-3 Billion Years
The average surface temperature will have increased to a rather stifling 147 degrees and even the remaining microbial colonies which, by now, will be residing in caves deep underground or lakes in the highest mountains, will die out. Earth will be a completely dead world which, over the next half a billion years, will present similar conditions to those of Venus today – extremely hot, dead and obscured beneath an extremely thick layer of clouds reflecting almost all of the Sun’s light back into space.
The Sun Becomes a Red Giant, 5.4 – 7.9 Billion Years
In 5.4 billion years, the Sun will no longer be a main sequence star and will move to the next stage of its stellar evolution as a red giant. Rapidly expanding, Mercury will likely end up being swallowed completely by the Sun and Venus will follow. Earth may also get devoured by the Sun, although it is more likely that it will get pushed further out into orbit. After 7.9 billion years, the Sun will reach its maximum size, sporting a radius about 256 times greater than it does now. Within a relatively short time after this, it will have spent all of its hydrogen fuel and will start to shrink dramatically to become a tiny white dwarf composed mostly of carbon and oxygen. At this point, Earth, if it even exists at all, will become a frozen, airless chunk of rock floating lonely through space for billions of years to come.