Terrestrial Life May Not Have Started On Earth

The history of life on Earth began long after the planet's formation 4.6 billion years ago. During the earliest stage of Earth's existence, the Hadean eon, the planet was simply a toxic fireball for roughly 6 million years. However, during this eon, something known as the heavy bombardment stage occurred, wherein the planet was hit with all manner of space debris, including asteroids. While life wouldn't emerge until the following eon, the Archean eon, the heavy bombardment stage may actually have been crucial to the eventual rise of life on Earth.

The first attempt by the United States to retrieve samples from an asteroid and bring them to Earth for analysis has revealed evidence that points towards asteroids potentially being responsible for bringing the building blocks of life to our planet. The findings reveal some interesting characteristics of the asteroid which suggest that the necessary conditions for the emergence of life existed in the solar system long before life emerged on Earth. Not only does this point to asteroids potentially bringing to our own planet some of the foundational elements needed for the emergence of life, it increases the odds that life could well have formed on other planets and moons in our solar system.

A pair of studies published in January 2025 detailed how NASA's OSIRIS-REx spacecraft traveled to Bennu, a small asteroid thought to have broken away from a larger one. The OSIRIS-REx mission was launched in 2016, with the spacecraft returning to Earth in September 2023 with 4 ounces of dust and pebbles from Bennu's surface. 

Now, as detailed in one of the papers, from the journal Nature Astronomy, the samples have been analyzed and found to contain sodium-rich minerals, amino acids, formaldehyde, and nitrogen in the form of ammonia. Fourteen of the 20 amino acids needed to make proteins were found in the samples, which are foundational elements of living organisms. Researchers also discovered five nucleobases which form the components of DNA and RNA in life on Earth. The high amount of ammonia was also significant as can it react with the formaldehyde to potentially form molecules such as amino acids, which when linked together can form proteins that power biological function.

This is significant as it suggests that the raw ingredients of life existed on Bennu's parent asteroid, hinting at the possibility of life existing in the solar system before it existed on Earth. As NASA's Daniel Glavin, co-lead author of the Nature Astronomy paper, said (via CBS News) the organic molecules found in the samples from Bennu are "real extraterrestrial organic material formed in space and not a result of contamination from Earth."

While the Nature Astronomy study doesn't confirm that life itself was present on the parent asteroid, it does confirm that the conditions that would give rise to life on Earth were present — especially when combined with the findings of a separate analysis of the samples.

While Daniel Glavin and his team analyzed the Bennu samples, a separate team lead by Tim McCoy, curator of meteorites at the Smithsonian's National Museum of Natural History in Washington, and Sara Russell, cosmic mineralogist at the Natural History Museum in London, carried out their own analysis. The team published its paper in the journal Nature, detailing how it found a history of saltwater that might well have served as the perfect environment in which the aforementioned compounds could combine.

McCoy, Russell, and their fellow researchers confirmed the presence of 11 minerals that were left behind by evaporating saltwater. Calcite, halite, sylvite, and eight other mineral traces were found, suggesting that the parent asteroid of Bennu was home to an environment conducive to life. That is to say there may have been lakes or even oceans on Bennu's parent asteroid, which when they evaporated left behind the minerals detected by McCoy and Russell's team.

To be sure, the minerals found in the samples from the OSIRIS-REx mission have been detected in meteorites before. But those examples were from meteorites that fell to Earth's surface. Until the Bennu samples were analyzed, researchers had never found a complete set of minerals that detail the process of saltwater evaporation across thousands of years or more. What's more, the mineral trona was found in the samples, representing the first time such a mineral was detected in extraterrestrial samples. Together, they point towards bodies of water that could have provided the right environment in which Glavin's molecules might have combined and potentially formed life.

The discoveries from the OSIRIS-REx samples are remarkable for many reasons. Not only do they show that molecules required for the emergence of life were present on an extraterrestrial object, but that they likely existed in an environment conducive to life itself. As such, they add to an overall picture of a solar system capable of producing life, but there are many questions that remain.

For one, we have still only found life itself on Earth and are yet to find concrete proof of life on any other planet or moon in our solar system, despite the evidence of building blocks being present on extraterrestrial bodies — such as Bennu and its parent asteroid.What's more, the samples from Bennu increase the odds that asteroids, though they can pose threats to Earth, could well have brought the building blocks of life to our planet billions of years ago. As such, the heavy bombardment stage could well have been a moment in the planet's history that, while hugely destructive, also provided the raw materials required for life to get started. That said, the exact origin of life on Earth remains unconfirmed.

Researchers are eager to carry out more testing to better understand the Bennu samples, as well as samples taken from other bodies. Meanwhile, the OSIRIS-REx spacecraft has been renamed OSIRIS-APEX and will now be used to explore the asteroid Apophis in 2029.  As more evidence is gathered, we will surely get closer to answering the question of whether we're alone in the universe, or indeed, in our own solar system.