When OSIRIS-REx sampled Bennu, it returned 250 grams (8.8 ounces) from the surface of the asteroid for study. Dating showed the material was 4.6 billion years old and contained amino acids, nucleobases, ammonia, formaldehyde and traces of saltwater brine. Scientific American ran a January 29, 2025, headline, “Asteroid Bennu is Packed with Life’s Building Blocks, New Studies Confirm.”
On Bennu’s surface were all the precursor ingredients needed for life:
- Amino acids are the building blocks of proteins.
- Nucleobases make up the base pairs in DNA and RNA molecules.
- Prebiotic molecules are necessary to synthesize sugars.
- Saltwater serves as the medium in which all of the above interact.
Some might argue that Bennu is a single sample and shouldn’t be considered representative of other asteroids. Except that would be wrong. Samples from the asteroid Ryugu, obtained by JAXA with Hayabusa2, also contained organic molecules, including 15 amino acids. Then there are the carbonaceous chondrite meteorites that have reached the Earth’s surface, which, when sampled, show the presence of amino acids, nucleobases, sugars, and more. These aren’t post-arrival contaminants, but rather being delivered from out of this world. What this more than suggests is that life’s origin isn’t confined to Earth, but rather is a product of the gas clouds and nebula found in the cold environment of space.
Panspermia Versus Abiogenesis
Panspermia
A Swedish chemist, Svante Arrhenius, coined the term panspermia back in 1908. He wasn’t the first to propose life’s origins from elsewhere, not Earth. That thought was first expressed by Anaxagoras, a Greek philosopher in the 5th century BCE.
Arrhenius was a pretty smart guy. I’ve written about him before because it was he who described the greenhouse effect, global warming and the correlation between human industrial activity and increases in atmospheric CO₂.
Panspermia comes in several flavours:
- Pseudopanspermia is the one that appears to fit the current evidence, the transfer of organic molecules from space to Earth.
- Lithopanspermia proposes that already formed life embedded in rocks ejected from other worlds gets transported to Earth.
- Radiopanspermia theorizes that cosmic radiation may have been the force to push dust-borne life to Earth.
- Directed panspermia is the stuff of science fiction, involving advanced alien civilizations seeding planets with life.
Whichever you fancy, the presence of life precursors found on bodies in space other than Earth supports panspermia. If the building blocks of life are everywhere in space, the panspermia argument holds water.
Abiogenesis
Abiogenesis presents an alternate theory. It proposes that life emerged during Earth’s early history. Probably between 4 and 4.5 billion years ago, as the numerous collisions of protoplanet bodies formed Earth and its atmosphere, conditions for abiogenesis emerged.
Early Earth was hot. Geologists call the period the Hadean Eon, taking the term from the Greek hellish underworld. The atmosphere was mostly CO₂ and nitrogen (N₂), with significant water vapour (H₂O) and smaller amounts of methane (CH₄) and ammonia (NH₃). The crust cooled. The first oceans emerged.
The conditions to lead to abiogenesis were there with sugars and nucleobases combining to produce the RNA World hypothesis, self-replicating RNA, followed by the emergence of proteins, which then “begat,” borrowing a term from Genesis, DNA.
Other sources associated with the abiogenesis theory for the origins of life on Earth point to niche environments that may have been the catalyst. Hydrothermal vents are one, and wet-dry cycles impacting surface ponds are another. Theoretically, both could have produced concentrated organics with the right chemistry to fuel self-organizing, prebiotic reactions to link amino acids to RNA.
A 2025 paper published in Astrophysics presents a hypothesis with 10:1 odds that life rapidly emerged on Earth under these “favourable” conditions.
In the end, both panspermia and abiogenesis could equally be right in a Universe filled with rich molecular chemistry and conditions suitable for life to emerge over billions of years.
