Humans owe their existence to astronomical coincidence

Earth is an extraordinary planet. For billions of years it has maintained the conditions that allowed life to develop. It was an extraordinary luck for the people.

Is life on Earth the result of the enormous resistance of organisms to external influences, or the work of a huge coincidence? Studies that simulated the evolution of the planetary community of living organisms over billions of years of Earth development point to the second possibility.

A planet without extremes

Conditions on and around Earth have changed significantly over time. For example, also because the Sun used to be up to a third less bright than it is now. The proportion of greenhouse gases in our planet’s atmosphere also varied.

But we know from geological data that temperatures have never (yet) gone to an irreversible extreme, although during the ice age 700 million years ago there was a threat that our planet would freeze forever.

Planetary biologists have not yet agreed on what is behind the resilience of life on Earth. There are basically two hypotheses as to how conditions could have remained relatively stable and not deviated to extremes over a long period of time.

The first hypothesis is that the Earth has a self-regulating system. Temperatures could not deviate too much because the risk of deviation triggered a system response to prevent it.

According to the second hypothesis, life on Earth was simply very lucky.

The second hypothesis is supported by a series of simulations carried out by Professor Toby Tyrrell from the University of Southampton.

When chaos piles up…

Tyrrell reached for the powerful computer. In it, he created an ensemble consisting of hundreds of thousands of (fixed) planets with random initial climate conditions. For each planet, he simulated further development hundreds of times.

Part of the simulations described on the website Communications Earth & Environmentwere both models of gradual changes as well as random events such as a supervolcano eruption or an asteroid impact.

In the simulation, the planets could turn out like us, but also like cold Mars or hot Venus. The simulations ended when the temperatures of the planets reached some extreme.

And the result? On average, only once in 100,000 simulations did the self-regulating system work, so that the world there could return to the temperature optimum and the conditions allowing (but not guaranteeing) life could persist.

For a simulated planet to be habitable for three billion years, as happened with Earth, it would have to be incredibly lucky. Even the planets that Tyrrell had simulated with the initial self-regulating system eventually fell into uninhabitability due to the accumulating chaos.

“Earth’s continuously stable and habitable climate is a mystery. Our neighbors, Mars and Venus, do not provide such conditions for life. “Earth has had a habitable temperature that it has maintained for three to four billion years — and that’s an extraordinary geological time,” Tyrrell wrote of the study.

‘Only gold fly’

The simulation records the interpretation that we Earthlings were literally astronomically lucky that the Earth remained habitable for three to four billion years, thus allowing them to evolve.

The hypothesis of a self-regulating Earth has had significant cracks before. It is probably true that life on Earth, as we know it today, is capable of changing its environment to some extent (even if we exclude human influence from life). But complex, maximally extended life has been present on Earth for barely half a billion years.

This means that the Earth could not have self-regulating ability before that.

If the self-regulatory capacity would depend not on life, but on erosion and volcanism, then another objection is offered – what about Mars and Venus? The first world is cold like Antarctica, the second is hot like the inside of a volcano. Shouldn’t similar self-regulatory mechanisms, if based on inorganic phenomena, also work on them?

Tyrrell’s simulations, as well as the thousands of known exoplanets, suggest that even if Earth had some as-yet-unknown regulatory mechanism, its very existence would be a stroke of luck.


Communications Earth & Environment

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