Scientists propose new theory for Earth's formation

Scientists have studied Earth for so long, but some questions remain unanswered. An international research team led by ETH Zurich and the National Center for Competence on Planetary Research proposes a new answer to the question- how the Earth was formed.

The prevailing theory suggests that the Earth was formed from chondritic asteroids. These are relatively small and simple blocks of rock and metal that formed in the early solar system. However, the problem with this theory is that no mixture of these chondrites can explain the exact composition of Earth, which is much poorer in light, volatile elements such as hydrogen and helium than expected.

Over the years, many theories have been proposed to explain this difference. For example, it was proposed that the objects that later became Earth collided and generated tremendous heat. Light components are evaporated; consequently, left the planet with her current makeup.

The study’s lead author, Paolo Sossi, Professor of Experimental Planetology at ETH Zurich, said, “Isotopes of a chemical element all have the same number of protons, even though the number of neutrons is different. Isotopes with fewer neutrons are lighter and should therefore be able to escape more easily. If the theory of evaporation by heating were correct, we would find far fewer isotopes of light on Earth today than in the original chondrites. But that’s exactly what the isotope measurements don’t show.”

Scientists, in this new study, are looking for another solution.

Sosie explained, “The dynamic model used to simulate planet formation shows that the planets in our solar system formed progressively. The tiny grains grew over time into kilometer-sized planetesimals by accumulating more matter through their gravitational pull.”

“Similar to chondrites, planetesimals are also small bodies of rock and metal. But unlike chondrites, they have been heated enough to differentiate into a metallic core and a rocky mantle.

“What’s more, planetesimals that form in different areas around the young Sun or at different times can have very different chemical compositions. The question is whether random combinations of different planetesimals produce compositions that match the composition of Earth.”

Scientists ran simulations in which tens of thousands of planetesimals collided in the early solar system to find out. The model was created in a way that allows gradual replication of the four rocky planets, Mercury, Venus, Earth, and Mars. Simulations suggest that Earth’s arrangement may have been the result of a combination of many planetesimals. Furthermore, the most statistically probable outcome of the model is the arrangement of the Earth.

Sosi remember, “Even though we expected it, we still found this result to be quite extraordinary. Not only do we now have a mechanism that better explains the formation of the Earth, but we also have references to explain the formation of other rocky planets.”

“The mechanism can be used, for example, to predict how Mercury’s composition differs from that of other rocky planets. Or how rocky exoplanets from other stars might be composed.”

“Our study shows how important it is to consider dynamics and chemistry when trying to understand planet formation. I hope our findings will lead to closer collaboration between researchers in these two fields.”

Journal Reference:

1. Sossi, PA, Stotz, IL, Jacobson, SA et al. Earth’s stochastic accretion. Nat Astron (2022). DOI: 10.1038/s41550-022-01702-2

#Scientists #propose #theory #Earths #formation