Quirks & Quarks

Do you feel lucky? Chance likely played a major role in life persisting on Earth

A simulation of 100,000 Earthlike planets ended with very few remaining habitable for the billions of years we'd expect it to take for life to evolve.

A simulation of 100,000 Earthlike planets had very few remaining habitable for billions of years

An illustration of an Earthlike exoplanet (NASA)

A scientist who ran simulations of the evolution of 100,000 possible planets has concluded that the chance of any particular planet remaining habitable long enough for life to evolve intelligence are quite small.

Professor Toby Tyrrell's work suggests that not only would the rise of intelligence on other planets rely on good fortune, but that life on Earth was very lucky to not experience a complete extinction before human intelligence arose.

Tyrrell was investigating what's called the "habitability problem." Scientists have long wondered just what maintained the habitability of a planet in the face of naturally fluctuating radiation levels from its star, catastrophic vulcanism and cosmic impacts.

Any of these events can disturb a habitable planet's climate enough to result in it freezing into a permanent iceball, or heating up so that its oceans boil away. On an Earthlike planet, for example, only a slight increase or decrease in the rate that the geosphere takes up or releases carbon dioxide could result in a permanent deep-freeze or catastrophic global warming.

Some researchers have suggested that on living planets, natural mechanisms act to stabilize climate, and correct for the influence of climate disturbances. If this is the case, then life is more inevitable, and luck plays a less important role.

Tyrrell decided to test this through computer modelling. He generated a "zoo" of 100,000 potentially habitable planets, and ran them through climate simulations over three billion years.  Each planet's fate was simulated 100 times. 

An illustration of what the exoplanet Kepler-1649c could look like from its surface. New research suggests that habitability may be a very temporary condition for most planets. (NASA/Ames Research Center/Daniel Rutter)

In his virtual experiment only one planet was habitable through every simulation. Fewer than nine per cent were successful in maintaining habitability in even one of their 100 runs.

"From that we deduce that it's almost certain there was a degree of chance in Earth having stayed habitable, that it wasn't something guaranteed from the outset," said Tyrrell.

According to Tyrrell's study the implications of this are that despite the large number of potentially habitable planets we now think exist in our galaxy, relatively few likely maintained a stable climate long enough for intelligent life to arise.

You can listen to Professor Tyrrell's interview with Bob McDonald using the link above.

Produced by Bryce Hoye, written by Jim Lebans

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