Earth’s oxygen-rich atmosphere will only last for another billion years
Life thrives on planet Earth thanks to oxygen. Oxygen is a highly reactive element; it can form compounds with almost any other element on the periodic table, releasing energy in the process. In a process known as cellular respiration, organisms use oxygen to oxidize substrates (eg sugars and fats) and generate energy.
The Earth formed about 4.6 billion years ago. Intense volcanic activity released gases that formed a toxic atmosphere, possibly a mixture of carbon dioxide, methane, ammonia and water vapor. Traces found in ancient rocks suggest that there are about 2.7 billion to 2.8 billion oxygen for the first time in Earth’s atmosphere, forming new minerals like iron oxide. Scientists believe that the first photosynthetic microorganisms, able to use sunlight to chemically break down carbon dioxide molecules into carbon and oxygen, resulted in a decrease in the amount of carbon dioxide and an increase in l ‘oxygen. But only about 2.45 billion to 1.5 billion years ago, oxygen was becoming an important part of the Earth’s atmosphere. Today, the Earth’s atmosphere contains 78 percent nitrogen and about 21 percent oxygen.
Scientists all agree that life cannot last forever on planet Earth. As the aging sun warms up, Earth’s oceans evaporate and the atmosphere escapes into space. Eventually, the sun will run out of energy and destroy itself along with the inner planets, including Earth.
A pair of researchers from Toho University and NASA Nexus for Exoplanet System Science have found evidence, by simulation, that Earth will lose its oxygen-rich atmosphere in about 1 billion years. In their article published in the journal Nature Geoscience, Kazumi Ozaki and Christopher Reinhard describe the factors that went into their simulation and what it showed.
The researchers created a simulation of the Earth taking into account variables describing the climate as well as geological and biological processes and, above all, the activity of the sun.
Climate, erosion, volcanism, plate tectonics all play a key role in regulating the level of oxygen at different times, but by far the most important factor, the only process actively producing free oxygen. , are oxygen producing organisms such as plants and algae.
The simulation shows that as the sun gets hotter, in 1 billion years, releasing more energy, the levels of carbon dioxide in the Earth’s atmosphere will begin to drop due to the gas absorbing the heat and decomposing. In a warmer climate, increased rates of chemical weathering will trap oxygen and carbon in rocks like limestone (or CaCO3). At the same rate, the upper layer of the atmosphere is absorbing more energy from the sun. With more kinetic energy available, the light oxygen molecules will escape Earth’s gravitational pull in space. The concentration levels of heavy molecules, like methane, will increase relatively compared to today.
As carbon dioxide levels drop, photosynthetic organisms, like algae in the sea and higher plants on land, will begin to suffer, reducing oxygen production. Over a period of only 10,000 years, carbon dioxide levels will drop so much that plant life will be lost. Without plant life, oxygen levels will also drop, causing a mass extinction event in the animals.
The result, according to the simulation, would be a planet with a higher nitrogen-methane-rich and lifeless atmosphere. Anaerobic creatures, microorganisms that instead of oxygen use other elements, like sulfur and methane, for cellular respiration, could still survive in underground habitats, like caves or cracks in the rocks. Since microbes are the first form of life on Earth, which appeared around 4 billion years ago, they will also be the last.
The researchers suggest their simulation could be of use to those seeking higher life on other planets – the window of opportunity, they note, may be shorter than previously thought, perhaps only 20 at 30% of the total lifespan of a planet.