When you look around you, almost everywhere on Earth, you see life. The earth seems to be an excellent support for life: we see it in the air, in the water, in the land, and even deep underground.
But was that inevitable? We know that there have been massive extinctions in the past, some of which have destroyed most of life on Earth. However, since life began and spread across the Earth, that has never happened all the way exterminated life. Of course! Otherwise, we wouldn’t be here to think about it.
Still it is interesting. This means that despite some severely disabling transient events, the Earth’s climate has remained relatively stable for 3-4 billion years.
That’s weird too. We know that stars like the sun get hotter with age, and that long ago the sun was about 30% fainter. That means either the old earth should have been frozen or, assuming it was mild, the earth should now be scalding hot. Neither is true, which is a mystery.
Called the Faint Young Sun Paradox, this has led many scientists to believe that Earth has some kind of thermostat, a set of conditions that tend to rebalance a system that comes out of whack so that it doesn’t get too hot or too warm. common cold. This would be a negative feedback system, where if a condition arises to warm up the Earth, for example, things will change in a way to cool it back down.
But we also know that there are conditions for positive feedback. If you release too much carbon dioxide into the air, the oceans will warm up, releasing more CO2, and you get a feedback loop that ends badly. As we see now. And if there is too little CO2 the earth would be frozen in the air.
So maybe we’re just lucky, and our environment just happens to have been stable for all those eons of life.
So is it accidental or by some mechanism? Or both?
To find out, a scientist conducted a clever experiment. He created a simulation of 100,000 planets (!!) where each got a series of random climate feedbacks, some negative and some positive, and tracked their temperatures for 3 billion years – no other variables (e.g. water content or breathing atmosphere) were simulated. For simplicity, he just wanted to see if a planet can maintain a habitable temperature for a long time, like Earth has.
To be clear, the simulated feedbacks were not based on real feedbacks such as CO2 in the air; instead, he randomly assigned the planets mathematical feedbacks, strictly numerical situations to see what would happen. He also threw larger random changes at random times to simulate external temperature forcing, similar to things like asteroid impacts or super volcanic eruptions.
Each planet sim was then run 100 times, with the variations in it slightly changed, to see what happens to the temperature.
The point here was not to create a full climate simulation, but to see how big the role of chance plays in a planet’s habitability. He tested two hypotheses. Hypothesis 1 is that feedback has no effect, so random fluctuations control the day; it is pure coincidence if a planet remains within a habitable temperature range for billions of years. The second hypothesis is that having feedback, negative or positive, warranties success or failure, where chance does not play a role.
In other words, he was hoping to see if climate feedbacks are really why the Earth has remained habitable for so long, or if we’re just lucky. A planet was considered habitable if its temperature remained relatively stable over the simulation for 3 billion years.
What he found is interesting. Of the 100,000 planets, 9% were successful at least once (and 1,400 were successful on the very first run of 100 runs). Some planets were successful twice, some three times … and in fact, while looking over all 100,000 planets, he had between 1 and 100 successful runs each.
But only 1 planet had 100 successful runs out of 100. That is a robust planet, indicating that nothing could prevent it from being a nice place to live (and least in terms of temperature).
Overall, looking at the set of outcomes and how they occurred, his conclusion is that both feedbacks and random chance play a role in a planet’s ability to stay in a habitable temperature range. Although the success rate varied from model to model, changing the factors over the 100 runs still supported the idea that both mechanism and chance played a role.
Apparently, fortune favors the prepared planet.
So can we extrapolate this to Earth, saying it’s both the feedback we have and the random chance that has kept our fair world, well, fair? If we rewind the tape and the circumstances vary a bit, would we still have a habitable world to live on?
I wouldn’t go that far. This seems to support that idea, but as the author himself said in the paper, “The simplifications and uncertainties in the model design mean that it must be unrealistic in some ways. Caution is therefore advised when extrapolating model results to reality. “
In other words, this is a very simplistic test, and much more complicated tests should be performed. After all, Earth has gotten close to the tipping point a few times, so it’s not hard to imagine a great asteroid impact or any other factor that gets us dirty. Yet this simulation is an interesting first step!
It does make a prediction: most of the exoplanets that resemble Earth will be uninhabitable, as that happened during most of its test runs. Planets such as Earth were the exception. If we find that to be true, it is not prove the hypothesis, but supports it. And if we really find most of it to be habitable, that will be interesting, won’t it?
And this serves as a cautionary tale. Not really know how robust the earth is, how well it can take a beating and how it keeps going. It has slammed, staggered, and shook things off in the past, but not without some degree of long-term environmental impact. And our own species, our civilization, is teetering on the razor’s edge right now. It wouldn’t take such a massive blow to deliver untold disasters to us, even if the Earth’s ecosystem somehow survived.
I have a lot of problems with people, but I prefer that we don’t die out. Unchecked fiddling with the feedback that’s already there seems like a pretty awful idea to me. The Earth may be robust, but we are not.
We have to be more careful. There is a reason why these things are mentioned cautionary stories.