The origin of life

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Life is the only major transition in this Journey that is bracketed rather than dated, and the bracket is wide. The upper bound is set by the Moon-forming impact and the subsequent cooling of the surface enough to hold liquid water, somewhere after about 4.4 billion years ago on the evidence of the Jack Hills zircons. The lower bound is set by the oldest evidence a majority of workers accept — the roughly 3.48 billion-year-old stromatolites and microbial textures of the Dresser Formation in Western Australia. Between those two figures sit the disputed claims: carbon-isotope evidence at 3.7 Ga at Isua, structures interpreted as stromatolites at the same locality and challenged eight years later, and haematite filaments in Quebec that may be 3.77 or 4.28 billion years old. Molecular reconstruction adds a fourth kind of claim entirely, with a 2024 study placing the last universal common ancestor around 4.2 Ga. What no source anywhere provides is a horizon that could be called the origin: every line of evidence dates the presence of established life, not its beginning.

A node is not a place. Drawing it on a map would assert something about the world that no stored fact supports.