Threshold 5 · Life on Earth

Emergence of Life

Chemistry becomes biology; life learns to use sunlight, remakes the atmosphere, builds complex cells and fills the seas and land.

3.5 billion years ago At least 3.5 billion years ago onward 0 of 8 lessons ready
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Threshold 1: The Beginning, 1 January, 00:00:00 1 Threshold 2: Formation of Stars, 5 January 2 Threshold 3: Chemicals Cook Up, 8 January 3 Threshold 4: The Early Earth, 2 September 4 Threshold 5: Emergence of Life, 30 September 5 Threshold 6: Collective Learning, 31 December, 23:48:33 6 Threshold 7: The Agricultural Revolution, 31 December, 23:59:32 7 Threshold 8: Modernity Strikes, 31 December, 23:59:59 8 Threshold 5 30 September
On the cosmic calendar this threshold begins on 30 September.

Somewhere in the first billion years of Earth’s history, chemistry crossed a line and became biology: molecules that copied themselves, varied, and were selected. We do not yet know exactly how. We do know what happened next, in extraordinary detail.

This chapter follows life from the last common ancestor of everything alive today through the microbial revolution that filled the air with oxygen, the invention of the complex cell, the sudden appearance of animal bodies in the fossil record, and the five great extinctions that cleared the stage again and again.

It ends with small, warm-blooded animals living in the shadows of the dinosaurs, waiting for their moment.

Lessons

  1. 5.1
    What is life?

    Why the most obvious question in biology has no agreed answer.

    Draft
  2. 5.2
    How chemistry became biology

    The hypotheses and evidence for the origin of life, and why the honest answer is that nobody knows.

    Draft
  3. 5.3
    Evolution by natural selection

    The one mechanism that turns chemistry into everything else.

    Draft
  4. 5.4
    The Great Oxidation Event

    How life poisoned the planet, and why we breathe the waste.

    Draft
  5. 5.5
    The complex cell

    The merger that happened once and made everything bigger than a bacterium.

    Draft
  6. 5.6
    The Cambrian explosion

    Why animal bodies appear suddenly in the rocks, and whether they really appeared suddenly.

    Draft
  7. 5.7
    Mass extinctions

    Five times the biosphere nearly ended, and what actually did the killing.

    Draft
  8. 5.8
    Mammals in the shadows

    A hundred and fifty million years of not being important, and what happened when the competition vanished.

    Draft

Disciplines