Exact time left for Earth in the habitable zone before ocean collapse
For as long as humanity has been aware, it has wondered when and how the end of the world will come. Far from apocalyptic prophecies, science has a much more calculated, cold and inevitable response, since it is clear that the Earth has an expiration date, or at least its capacity to host life as we know it does. It has been calculated. A classic study published in the magazine Astrobiology In 2013 by researcher Andrew Rushby, he calculated the “habitability window” that our planet has left. The magic number, popularized from these physical and climate models, is around at 1.8 billion yearswhich is the average value that we find in the range between 1,750 and 3,250 million years. The problem is that this date is not entirely real, since within 1.8 billion years there will be no type of life on our planet, but for human beings and complex life the expiration date is much earlier. The culprit. To understand how scientists arrived at the figure of 1.8 billion years, we must look at the Sun. And, like any star of its type, our Sun is subject to a process of stellar evolution that means that, as it consumes its nuclear fuelits core contracts and heats up, causing the outer layers to expand and, therefore, its luminosity does not stop growing. Here Rushby’s team did not make a simple random prediction, but rather their methodology consisted of combining models of this evolution of solar brightness with parameters of the greenhouse effect and the energy balance of the Earth. What they were looking for was to calculate the exact moment at which the Earth will leave the so-called “habitable zone.” A little further. The habitable zone is that orbital strip around a star where temperatures allow the existence of liquid water on the surface of a rocky planet. But as the Sun becomes brighter and hotter, that fringe moves toward the edges of the solar system, while the planet does not move from its orbit. And that is a problem. All this means that when the Earth crosses the inner limit of this zone, the increase in solar radiation will trigger a runaway greenhouse effect, similar to what Venus suffers today. The effects of this will be the evaporation of the oceans, which will contribute to the greenhouse effect, trapping heat even more and accelerating the process until the Earth loses its liquid water irreversibly. And with it life. Different types of life. It is crucial to differentiate what “habitable” means in astrobiological terms versus what we consider “habitable” in our daily lives. A very important fact is that the Earth is approximately 4.545 billion years old, and life in its simplest forms emerged surprisingly early about 3.7-4.3 billion years ago. With all this we mean that the end of life will be staggered, starting with affecting complex life like us, which are extremely fragile to thermal variations. This makes the authors emphasize that the conditions for animal and human life will be greatly lost before reaching those 1.8 billion years. The last to die. The Apocalypse of 1.8 billion years refers to the last breath of the planet. In that final scenario, when the oceans are evaporating, only the most resistant extremophile microorganisms will be able to survive in isolated niches such as pockets of groundwater at very high temperatures before facing total extinction. Looking to the future. At this point, one might wonder what point it is to calculate exactly when the oceans will dry up eons from now if humanity today has more pressing problems. And the answer lies in the search for other planets, since by perfectly understanding how the “window of life” evolves in our solar system, astronomers have tools to apply to exoplanets that we are discovering thousands of light years away. In this way, knowing how long a planet’s habitability lasts depending on its host star helps us know where to look. We may find a planet in the “habitable zone” of its star, but if calculations reveal that it has only been there for a few million years, it is likely that complex life has not had time to evolve yet. Images | Javier Miranda In Xataka | Ryan MacDonald, astronomer, on the future of the Earth: “The death of the star is not the end, but the beginning of a new chapter”