Earth Log 0008 The Long March Onto Land

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. What the planet still lacked, at the close of that entry, was animals in the modern sense, plants of the kind that build forests, and any biology at all on the dry continents above the tideline.

This entry covers the period during which all of that arrived. It begins in the deep freeze of the Cryogenian, runs through the Cambrian and the long Palaeozoic afterwards, and ends with the appearance of the egg that finally let the descendants of fish reproduce out of sight of standing water. It is the period during which life moved, decisively and visibly, from being a layer of slime and fronds in the sea to being a presence on the dry surface of the Earth.