Life on Earth may depend on a chemical Goldilocks balance during planet formation

An ETH Zurich study published in Nature Astronomy reports that the amount of oxygen present while a planet's core forms determines whether phosphorus and nitrogen remain at the surface; the authors say Earth formed about 4.6 billion years ago with a balance that kept both elements available for life.

Researchers report that the availability of phosphorus and nitrogen at a planet's surface depends on oxygen levels during the planet's core formation. These two elements are especially important for life as we know it, and their retention at the surface can be set by early chemical conditions. The work comes from a team at ETH Zurich and appears in Nature Astronomy. The authors link these processes to why Earth retained the necessary ingredients while some other planets did not. Key findings: - The study finds that the amount of oxygen present during core formation controls whether phosphorus and nitrogen remain in the planet's surface layers or are lost to the core or space. - If there is too little oxygen, phosphorus tends to bind to heavy metals and sink into the core, removing it from the surface. - If there is too much oxygen, the mantle can hold large amounts of phosphorus while nitrogen is less likely to remain and can escape into space. - The researchers say Earth formed about 4.6 billion years ago with an oxygen balance that allowed both phosphorus and nitrogen to stay at the surface. - The paper notes Mars may have been too far from the Sun to retain sufficient phosphorus or nitrogen for similar chemistry at the surface. - Because planets form from the same material as their host star, the authors suggest stellar composition could help narrow which systems are chemically suited to retain these elements. Summary: The study reframes habitability to include a "chemical Goldilocks" condition during planet formation that affects key life elements, not just surface temperature and water. The authors report this could make searches for life more specific by considering oxygen and stellar composition when assessing a planet's chemical suitability; the broader implications for exoplanet surveys are still being developed.