How Long Will Earth Be Able To Sustain Life?
By David Bressan The end of earth will come in 7.59 billion years, unfortunately the end for all life on earth will come much sooner. Various geological catastrophes, like the formation of large igneous provinces (in short LIPs), pose a real danger to life on earth. One possible explanation for the most severe crisis in earth’s history, the Permian–Triassic extinction event with an extinction rate of 96%, suggests that volcanic ash and gases from the large LIPs of Emeishan (China) and Siberia poisoned the entire atmosphere. The impact of a large asteroid, maybe together with volcanism, caused the last great mass extinction, with the dinosaurs as the most famous victims. But even without such catastrophic events life on earth will eventually perish. A stromatolite, such fossilized microbial mats are the oldest sign of life on earth and microbes will be also the last life forms on earth. Image by David Bressan. As the sun grows older also the emission of light and radiation increases, by almost 1% every 110 million years. In response global temperatures on earth will rise. Warmer temperatures cause more evaporation from earth’s oceans and more water in the atmosphere accelerates the erosion of rocks. Weathering and erosion binds large amounts of carbon-dioxide in marine sediments. The sediments are subducted into earth’s mantle, melt there and feed volcanic activity, so the stored carbon-dioxide is brought back into earth´s atmosphere. This cycle regulated and stabilized earth’s surface temperature in the last billion years and earth never was too hot or too cold for liquid water, a prerequisite of life. Eventually plate tectonics will stop as earth runs out of energy and erosion will prevail. More and more carbon-dioxide will be stored in sediments deposited on the bottoms of earth’s oceans. In estimated one billion years the concentration of carbon-dioxide in earth’s atmosphere will be too low to sustain plants or other phototropic organisms. Without plants also higher animals will have soon or later no food and starve to death. Without carbon-dioxide earth’s atmosphere will also lose an important gas to regulate its temperature. Strong variations will occur and eventually temperatures will drop far below the freezing point of water. Earth will become an ice planet like some moons today in our solar system. Microorganism maybe will be still around, feeding on chemical reactions along the last active hot springs under the ice or surviving in underground habitats, like caves and fissures in rocks. As microbes were the first life on earth, appearing some four billion years ago, they will be also the last survivors. In one to two billion years the sun will be so hot that all ice on earth will melt again, forming boiling oceans and an atmosphere composed mostly of water vapor. Some extremophiles are able to survive in 170 to 240°F (80 to 115°C) hot water and for a certain time the last oceans on earth will thrive with microbes adapted to high temperatures. As the sun becomes even hotter in two billion years all water on earth will eventually evaporate and lost into space forever. The surface will become a dry desert, too hot and inhabitable for life. The interior of earth, now completely solidified and inactive, will become too cold to provide energy or nutrients for the last existing life forms hidden underground. It seems improbable that any microorganisms, even extremophiles, will be able to survive at this point of earth´s history.