A single planetary feature may be critical to the emergence of complex life in the universe


A new study reveals that the axial tilt, like the tilt of the Earth, helps increase oxygen production, which is vital to life as we know it.

“The bottom line is that worlds that tilt modestly on their axis may be more likely to evolve complex life,” said planetary scientist Stephanie Olson of Purdue University. “This helps us narrow the search for complex, possibly even intelligent life in the universe.”

When looking for habitable worlds elsewhere in the galaxy, the first things we look for are: Are they relatively small and rocky, like Earth?

The presence of a magnetic field, for example, is thought to be very important, as it protects the planets’ atmospheres from stellar winds. The eccentricity of the planet’s orbit and the type of other planets in the system may also be key.

Olson and her team were a little more precise, looking at the presence and production of oxygen; Specifically, conditions on the planet that may affect the amount of oxygen produced by photosynthetic life.

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Most (though not all) organisms on Earth require oxygen to breathe – we cannot live without it. However, early Earth was low in oxygen. Our atmosphere became rich in oxygen only about 2.4 to 2 billion years ago, a period known as the Great Oxidation Event. It was activated by a mutation in cyanobacteria, which pump out massive amounts of oxygen as a metabolic waste product, allowing multicellular life to emerge.

Using modeling, Olson and her team sought to understand how the conditions under which cyanobacteria can thrive may arise.

“The model allows us to change things like the length of the day, the amount of the atmosphere or the distribution of land, to see how marine environments and oxygen-producing life in the oceans respond,” Olson explained.

Their model showed that several factors could influence the transport of nutrients in the oceans in a way that contributed to the emergence of oxygen-producing organisms such as cyanobacteria.

Over time, the Earth’s rotation slowed down, its days got longer, and continents formed and migrated. The researchers found that both of these changes could help increase the oxygen content.

Then they took into account the axial tilt. The Earth’s axis is not perfectly perpendicular to its orbital plane around the Sun; It is tilted at an angle of 23.5 degrees from the vertical. This tilt is why the seasons exist – the tilt away from or toward the sun affects seasonal fluctuations. Seasonal changes in temperature also affect the oceans, mixing convection, currents, and nutrient availability.

So perhaps not surprisingly, the axial tilt had a significant impact on oxygen production in the team’s study.

Planetary scientist Megan Barnett, from the University of Chicago, explained: “The larger tilt increased photosynthetic oxygen production in the ocean in our model, in part by increasing the efficiency with which biological components are recycled.”

The effect was similar to doubling the amount of life-sustaining nutrients.

“This work reveals how key factors, including a planet’s seasonality, can increase or decrease the possibility of finding life-derived oxygen outside our solar system,” said Timothy Lyons, a biochemist from the University of California Riverside.

The research was presented at a conference Goldschmidt Geochemistry for 2021.

Source: Science Alert


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