It took an evolution of 3 or 4 billion years to produce Homo sapiens. If the climate had completely failed just once in that time evolution would have stopped abruptly and we would not be here now. So to understand how we came to be on planet Earth, we need to know how the Earth got fit for life for billions of years.
This is no small problem. Current global warming shows us that the climate can change dramatically over even a few centuries. Over geological timescales, climate change is even easier.
Calculations show that the Earth’s climate has the potential to decline to temperatures under freezing or above boiling in just a few million years.
We also know that the sun has become 30 percent lighter since life first appeared. In theory, this should have caused the oceans to boil away before this time, as they were not generally frozen on Earth early – this is referred to as the “young sun ‘s paradoxes. But, somehow, this residential puzzle was solved.
Scientists have developed two main theories. The first is that the Earth could have something like a thermostat – a feedback device (or apparatus) that prevents the climate from ever going off to a lethal temperature.
The second is, out of a large number of planets, some may just be making it through with fortune, and Earth is one of those. This second scenario is made more plausible by what has been discovered in recent decades of many planets outside our solar system – so-called exoplanets.
Astronomical observations of distant stars tell us that many of them have planets connected to them, and that some of them are of size and density and orbital distance in order to theoretically be able to make them fit for life. It is estimated that there are at least 2 billion such candidate planets in our galaxy alone.
Scientists would like to travel to these exoplanets to find out if any of them have matched billions of years of climate sustainability. But even the nearest exoplanets, the ones orbiting the star Proxima Centauri, are more than four light-years away. It is difficult to come up with observational or experimental evidence.
Instead, I explored the same question through modeling. Using a computer program designed to simulate the evolution of climate on planets in general (not just Earth), I first created 100,000 planets, each with a different set of conventional foods. -weather. Climate nutrition processes are processes that can increase or decrease climate change – think for example of melting sea ice in the Arctic, which replaces ice exposed by sunlight with sunlight. an open sea that absorbs sunlight, which in turn causes more warming and more melting.
To study how likely it was that each of these diverse planets would survive over large (geological) time frames, I made a simulation every 100 hours. Each time the planet started from a different initial temperature and was exposed to a set of random climate events.
These events represent climate-changing factors such as supervolcano eruptions (like Mount Pinatubo but much larger) and asteroid effects (like the one that killed the dinosaurs). On each of the 100 runs, the planet’s temperature was monitored until it became too hot or too cold or otherwise to survive for 3 billion years, at which time it was estimated that it is a capable bruise for a sensible life.
The results of the simulation provide a definitive answer to this residential problem, at least in terms of the importance of life and fortune notices. Rarely (in fact, only once out of 100,000) did a planet maintain such strong sustained support that it remained inhabited for 100 hours, regardless of random climate events.
In fact, most inhabited planets lived at least once, less than ten times out of 100. Almost every time in the simulation when a planet remained lived for 3 billion years, it was partly due to fortune.
1,000 different planets were randomly created and ran twice. Green circles show a capacity for 3 billion years. (Toby Tyrrell)
At the same time, it was shown that fortune alone was not enough. Planets specifically designed to have no food at all did not remain; walks were not random, with climate events surrounding the course.
This overall result, that results are largely dependent on feedback and partly on fortune, is strong. It was not affected by all sorts of changes to the model. By the way, so the Earth must have some climate-sustaining foods but at the same time good fortune must be involved in living as a place to live.
For example, if an asteroid or solar flame had been slightly larger than it was, or had occurred at a slightly different (more critical) time, we might not have been here on Earth today.
It takes a different view of why we are able to look back on the wonderful, expanding life history of the Earth growing and multiplying and becoming increasingly complex to the extent that it has given us. . 
Toby Tyrrell, Professor of Earth System Science, University of Southampton.
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