Researchers at the University of Copenhagen have reconstructed planetary formation data to reveal that Earth and Mars developed through distinctly different evolutionary paths 4.5 billion years ago.
When our Solar System coalesced from a swirling cloud of gas and dust four and a half billion years ago, neighboring planets grew side by side. Planetary scientists have long debated the exact mechanics behind how rocky bodies like Earth and Mars emerged from that primordial disk. The central question has hinged on whether giant space rocks collided to form planets or whether those large bodies accumulated smaller particles over time.
Chemical Fingerprints in Planetary Mantles
To solve this ancient puzzle, investigators examined the outer crust and mantle layers of both worlds. They focused particularly on volatile elements such as zinc, sodium, and potassium, which evaporate relatively easily under high temperatures. These elements act as chemical fingerprints, recording the thermal conditions and processes each planet experienced during its accretion.
It is a major detective job to figure out what happened back then when most of the evidence disappeared long ago. But even after 4.5 billion years, the compositions of Earth’s and Mars’ mantles remain the same. You can think of them as an imprint of the formation process.
Professor Anders Johansen, Globe Institute, University of Copenhagen
Using advanced statistical computer modeling, the research team simulated various formation scenarios to determine which processes best fit the observed chemical profiles. Their analysis supports the hybrid model of planetary formation, which combines giant impacts with the accumulation of smaller material. However, the exact proportions of those building blocks diverged sharply between the two neighbors.
Divergent Paths of Earth and Mars
The study reveals that Earth accumulated the vast majority of its mass through the gathering of pebble-sized particles by large protoplanets, while Mars grew primarily from collisions between massive planetesimals. According to the findings published in the scientific journal Nature Astronomy, the structural origins of the two inner planets look remarkably dissimilar.
At least 75 percent of Earth’s mass appears to originate from two young planets, known as protoplanets, that grew large by accreting pebbles, while planetesimals contributed up to 25 percent. In contrast, roughly three-quarters of Mars’ mass appears to come from planetesimals, with the remaining quarter originating from pebble accretion.
Assistant Professor Haiyang Wang, University of Copenhagen
The Copenhagen team acknowledges that their computer simulations rely on certain assumptions. The models assume that the original planetesimal building blocks shared a chemical composition similar to the asteroid Vesta and that volatile elements vanish more efficiently during pebble accretion than during giant impacts. Yet even when adjusting for those variables, the primary conclusion holds firm that the two worlds formed through separate dominant mechanisms.
NASA’s Goddard Instrument Field Team traveled to the Scottish Highlands to examine the rocks and cliffs of the Stoer formation, which share environmental characteristics with ancient Martian lakes and rivers reported by NASA.
These terrestrial field sites hold microbial life evidence from 1.2 billion years ago, offering a crucial baseline for scientists studying data returned by rovers searching for ancient biosignatures. NASA’s Perseverance rover continues hunting for signs of past life inside Jezero Crater.
As exciting and surprising as these findings were, it’s still not incontrovertible evidence of life.
Melissa Rice, planetary science professor at Western Washington University and Perseverance team member
Although organic molecules discovered by the rover strongly suggest the possibility of ancient microbial activity, researchers emphasize that non-biological chemical reactions could also produce similar signatures according to Western Washington University. Scientists agree that definitively resolving whether those Martian samples represent true biosignatures will ultimately require returning the physical rocks to laboratories on Earth.