Collection

The question seems narrow, but the answer turns out to be most of what matters. By the time the period covered in this entry ends, the air had been remade, the ozone layer had formed, the oceans had begun to clear of dissolved iron, an entirely new kind of cell had been invented, sexual reproduction was in operation, and the first organisms had begun to live in cooperative bodies of many cells working as one. None of the species a casual modern observer would recognise existed yet. There were no animals, no land plants, no macroscopic fungi.

The previous entry ended in the late Carboniferous, in the swamp forests of what is now Nova Scotia, with a small lizard-like animal sheltering inside a hollow tree. That animal, Hylonomus, was an early amniote — a member of the lineage whose innovation, the amniotic egg, had freed vertebrate reproduction from the need for standing water. With that freedom, the dry interior of the continents was open to vertebrates for the first time.

How did the descendants of a small Carboniferous amniote come to include both an albatross and a human being?

In the previous entry I described what humanity at this time understands about how life began on Earth — the chemistry that produced the first replicating molecules, and the moment at which ordinary matter first acquired the property of making copies of itself.

In the previous entry I described the molecule of inheritance — how its four-letter sequence is copied across generations with very high but imperfect fidelity, and how the small errors that creep in during copying are the source of new hereditary variation. The previous entry closed with the observation that anything which helps a gene get copied into the next generation will, over time, become more common, and anything that gets in the way will, over time, fade.

The previous entry described the first two billion years of life on Earth — a long, almost entirely microscopic stretch in which the chemistry of cells was worked out, the atmosphere was remade, and the cooperative architecture of multicellular bodies was assembled in the oceans. By its end, eukaryotic cells were established and several lineages had begun to live in cooperative bodies of many cells working as one.

Where possible, I cite sources from which I made inferences so that future readers — should they recover the technical literature of this era — can trace specific claims back to their origins and assess them for themselves. References are listed, in numbered form, at the end of each entry.

How did living things arise on a planet that was, at first, not living?

In the previous entry I began recording events unfolding during my lifetime — conflicts between nations and the uncertainties of the present moment. Those events belong to the immediate history and concerns of our species, which I will continue to document in future logs. In this entry, however, I step much further back in time to describe what we currently understand about our origins, beginning with the origins of the universe.

As I noted in my first log, groups of my own species are now engaged in armed conflict with one another. The situation is unstable and expanding. There is a real possibility that these conflicts could draw in many nations across the planet, potentially leading to a war of such scale and destructive power that it could threaten the survival of our civilization—and perhaps even our species.

Because of this, I feel compelled to record events as they happen, even if the broader background that would help you understand them must come later.

Our star is one of hundreds of billions inside a galaxy we call the Milky Way. Humans have only recently come to understand how vast the universe is, and how small our world is within it.

I am writing these logs during my lifetime to record what it is like to live as a human in this moment of history.