It took evolution 3 or 4 billion years ago To produce Homo sapiens. If the climate had completely failed only once in that time, evolution would have completely stalled and we wouldn’t be here now. In order to understand how we arose on planet Earth, we will need to know how Earth has managed to survive a decent life span of billions of years.
This is not a trivial problem. Current global warming shows us that the climate can change dramatically over the course of a few centuries. Over geological time scales, it is easier to change the climate.
Calculations show that there is a possibility that Earth’s climate will degrade to temperatures below freezing or above boiling point in just a few million years.
We also know that the sun has gotten 30 percent brighter since life first evolved. In theory, this should have caused the oceans to boil now, given that it wasn’t Generally Frozen to the ground early — this is known as «Faint youth of the sun paradoxHowever, somehow, the habitability puzzle has been solved.
Scientists came up with two main theories. The first is that Earth could have something like a thermostat — a feedback mechanism (or mechanisms) that prevent the climate from roaming into deadly temperatures.
The second is that among a large number of planets, some may have succeeded in passing through luck, and Earth is one of them. This second scenario is made more plausible by discoveries in recent decades of many planets outside our solar system — the so-called Exoplanets.
Astronomical observations of distant stars tell us that many of them have planets orbiting them, and that some are of such size, density, and orbital distance that temperatures suitable for life are theoretically possible. It has been estimated that there is at least 2 billion of these are candidate planets In our galaxy alone.
Scientists love to travel to these exoplanets to check if any of them match up to a billion years of climate stability on Earth. But even the closest exoplanets are orbiting the star Proxima Centauri, More than four light years away. It is difficult to obtain observational or empirical evidence.
Instead, I explored the same question through modeling. Using a computer program designed to simulate the evolution of the climate on planets in general (not just Earth), first 100,000 planets were born, Each has a randomly different set of climate reactions. Climatic reactions are processes that can be enlarged or contracted Climate change Think, for example, about melting Arctic sea ice, which replaces sun-reflecting ice with an open sea that absorbs sunlight, which in turn leads to more warming and more melting.
In order to investigate how likely it is that each of these diverse planets will remain habitable on massive (geological) time scales, I simulated every 100 times. Each time the planet started out with different initial temperatures and experienced a randomly different set of climate events.
These events represent climate change factors such as Super volcano Bangs (eg Mount Pinatubo But much bigger) and asteroid Effects (like the one that killed Dinosaurs). In each round of the 100 cycles, the planet’s temperature was tracked until it became very hot or very cold or survived for 3 billion years, at which point it was seen as a potential melting pot of intelligent life.
The simulation results give a definite answer to the housing problem, at least in terms of importance of feedback and luck. It was so rare (in fact, only once out of 100,000) that a planet had such such strong stability feedback that it remained habitable 100 times, regardless of random weather events.
In fact, most planets that have remained habitable at least once, have done so less than ten times out of 100. On nearly every occasion in a simulation when a planet has been habitable for 3 billion years, luck was partly due to luck.
At the same time, luck in itself turned out to be insufficient. Planets specially designed to have absolutely no reflexes, never remained habitable; The random walk, which is prone to weather events, the path never lasted.
This overall score, results partly based on feedback and partly on luck, is strong. All sorts of changes to the modeling did not affect her. By implicitly, the Earth must thus have some reactions to stabilizing the climate but at the same time Good fortune It must also have participated in its remaining habitable.
For example, if an asteroid or solar flare was a little larger than it was, or it happened at a slightly different (more important) time, we probably wouldn’t be here on Earth today.
It gives a different view of why we have been able to revisit Earth’s so gorgeous and expansive history that is evolving, diversifying, and becoming more and more complex to the point that it gave rise to us.
Toby Terrell, Professor of Earth System Sciences, University of Southampton.
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