The question of how life originated on Earth, or how simple organisms emerged from chemical compounds, remains somewhat of a mystery. While scientists have confirmed, based on fossil evidence and the geological record, that life began approximately 4 billion years ago on the seafloor (around hydrothermal vents), it is still unclear how the ingredients for life arrived on Earth. The prevailing view is that they were delivered by comets and asteroids from the outer Solar System, which also brought surface water to Earth.
According to this theory, planetesimals transported these elements to the inner Solar System during the Late Heavy Bombardment, thought to have occurred between 4.1 and 3.8 billion years ago. However, new research supported by NASA provides fresh insights into how early Earth acquired the elements essential for life. The study’s findings, published in the journal Science Advances, suggest that Jupiter likely played a pivotal role in this process.
The research team comprises members from Rice University’s Department of Earth, Environmental and Planetary Sciences. As they note, the timing of light element delivery to Earth is still debated, as is the geochemistry of the planetesimals involved. Conventional models link this to outer Solar System chondrites – stony meteorites that formed two to four million years after the Solar System’s first solid bodies. However, as the team pointed out, this accretion age rules them out as the earliest source of light elements.
Stated simply, all life on Earth relies on the same fundamental elements, abbreviated as CHNOPS: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur. These elements were forged through the fusion of hydrogen and helium in the first generation of stars (Population III), which then dispersed into space as clouds of gas and dust when these massive stars exploded as supernovae at the end of their short lifespans (tens of millions of years). These and other heavier elements (including silicon, iron, and various metals) then coalesced to form subsequent generations of stars and planets.
Approximately 4.6 billion years ago, the Sun formed from a cloud of this gas and dust (a nebula) that underwent gravitational collapse at its center. The leftover material formed a disk around the new star, gradually accreting to form the Solar System’s planets and planetesimals. The remaining material settled into various orbits as asteroids and comets, with most residing in the main asteroid belt and the Kuiper Belt. Others fell into planetary orbits – for instance, near-Earth asteroids (NEAs) or Jupiter’s Trojan and Greek asteroids.
Over time, many of these objects crossed Earth’s orbit, impacted its surface, and were discovered as meteorites. Studying these objects provides a window into the early Solar System, a far more chaotic time when Earth was still forming. Meteorites fall into two categories, both originating from planetesimals formed at different times in our system. These include dense metallic objects (iron meteorites) and stony chondrites, the latter comprising the majority of those found on Earth.
The oldest planetesimals are the source of iron meteorites, while chondrites belong to a second generation that formed 2-3 million years later. Although some evidence suggests that outer Solar System chondrites delivered the ingredients for life late in Earth’s formation, scientists continue to debate which specific type of meteorite supplied Earth’s stores of L-elements (light elements). The new research proposes that events may have unfolded differently than traditional models suggest.
Using laboratory experiments and geochemical modeling, the team reconstructed a map of the phosphorus-to-nitrogen (P/N) ratio in the early Solar System. Their results showed that in the first generation of planetesimals (irons), objects had a higher P/N ratio in the outer Solar System, which decreased toward the inner system. This trend reversed in the second generation, where chondrites exhibited a higher P/N ratio in the inner Solar System.
The research team hypothesized that during the first generation of planetesimals, an outward flow of material increased the P/N ratio in the outer Solar System. This situation changed with the arrival of Jupiter, whose gravitational influence restricted the inward migration of phosphorus and nitrogen from the inner Solar System to the outer. This meant that by the time the second generation of planetesimals formed, those orbiting within the inner Solar System had a higher P/N ratio than their counterparts orbiting further from the Sun.
These findings indicate that, contrary to previous models, Earth received its phosphorus and nitrogen (both essential for life) predominantly from the inner Solar System, without significant contributions from the outer reaches. Their conclusions are supported by accretion geochemical models, which show that Earth’s current P/N ratio is best reproduced by inner Solar System planetesimals, regardless of whether they are associated with iron or chondrite meteorites.
“Jupiter’s presence and its evolutionary history in our Solar System appear to have played a crucial role in determining the distribution of key chemical building blocks necessary for habitable worlds. It remains an open question whether a balance of vital elements similar to Earth’s can be established without a Jupiter-like planet in the population,” said study co-author Rajdeep Dasgupta of Rice University.
“The study suggests that Earth acquired its stores of vital elements — phosphorus and nitrogen — mainly from the inner Solar System, without significant contribution from outer Solar System chondrites,” the scientists concluded.
As for other vital elements, the pathways through which they arrived on Earth billions of years ago remain to be discovered and will be the subject of future research.
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