Black stones land near an Australian town. Gather the Murchison meteorite's pieces and you have about a wheelbarrow load. Hidden in that rock are parts your cells use to build proteins.
The fall happened in 1969. Scientists have since found more than 80 kinds of amino acids, small molecules that can link like beads on a thread. Rock chemistry can make them without anything being alive.
Then comes the awkward question: did the stone pick those parts up from the soil? Scientists tested their shapes and the mix of heavy and light atoms. Much of the chemistry points beyond Earth, though dirt can add false clues.
So spacecraft went straight to Bennu and Ryugu and brought back sealed samples. They held carbon-based molecules too. Scientists call these organic molecules. The word does not mean a living thing made them.
Panspermia (pan-sper-mee-uh) is the idea that life's parts, or life itself, could travel between worlds. These rocks show that parts can arrive. Nobody has confirmed life in a meteorite. Some shielded bacteria survive years in space tests, but that does not prove a trip between planets. We know the chemistry travels. How it became life is still open.
Beyond the video
The idea is older than spaceflight. In 1871 Lord Kelvin, then the most respected physicist in Britain, told the British Association there were probably “countless seed-bearing meteoric stones moving about through space.” In the same speech he called the idea “wild and visionary” and claimed only that “it is not unscientific.” A century later Francis Crick and Leslie Orgel wrote the formal version in the journal Icarus. They ended by saying the evidence was “inadequate at the present time to say anything about the probability.”
Murchison holds more than amino acids. In 2019 a team led by Yoshihiro Furukawa reported ribose, the sugar in RNA, at about 25 parts per billion. Its carbon signature sits well outside the range of the sugars in the soil where the stone fell. The same rock contains specks of silicon carbide that formed around other stars before the Sun existed.
Comets carry this chemistry too. When NASA’s Stardust mission brought comet dust back to Earth, glycine in the sample passed the carbon-isotope test. A second compound failed it, and turned out to be nylon from the handling equipment. Later, the Rosetta spacecraft flew alongside comet 67P and measured glycine and phosphorus in the gas around it. Telescopes have done worse: a 2003 report of glycine in interstellar clouds did not survive a careful recheck, and no detection has been confirmed since. Sampling the material directly has proved far more reliable than looking at it from a distance.
Sources
- Thomson (Lord Kelvin), Presidential Address, British Association Report, 1871
- Crick & Orgel, “Directed Panspermia,” Icarus 19:341 (1973)
- Furukawa et al., PNAS 116:24440 (2019)
- Heck et al., PNAS 117:1884 (2020)
- Elsila, Glavin & Dworkin, Meteoritics & Planetary Science 44:1323 (2009)
- Altwegg et al., Science Advances 2:e1600285 (2016)
- Snyder et al., Astrophysical Journal 619:914 (2005)
