Amino acids
Amino acids are small carbon-based molecules, the building blocks of proteins, and some meteorites contain ones made without life.
Living things build proteins from about twenty kinds of amino acids. Each has a carbon backbone with an amino group (containing nitrogen) and an acid group. Remarkably, dozens of different amino acids have been extracted from carbonaceous chondrites, including many that life on Earth hardly uses at all.
The classic case is the Murchison CM2 chondrite, which fell near Murchison, Victoria, Australia, in 1969. Analyses soon after the fall found amino acids, and later work identified many more. How do we know they are not contamination? Several lines of evidence agree: the molecules include unusual types rare in biology, their carbon and hydrogen isotopes differ from Earth's, and they come in both left- and right-handed mirror forms, while life uses almost only the left-handed form. Some meteorites show small excesses of left-handed forms of certain amino acids, a finding that feeds debates about the origin of life's handedness. Samples returned from asteroid Bennu were reported in 2025 to contain 14 of the 20 amino acids used in Earth's proteins.
Amino acids cannot be seen. They are detected by chromatography and mass spectrometry, which is why careful, glove-on handling of fresh falls is so important.
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