Big History

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 2 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?

    Definitions of life, and the last universal common ancestor of everything alive today.

    Planned
  2. 5.2
    How chemistry became biology

    The hypotheses and evidence for the origin of life.

    Draft
  3. 5.3
    Evolution by natural selection

    The mechanism, stated precisely, and the evidence that it works.

    Planned
  4. 5.4
    The Great Oxidation Event

    How microbes remade the planet's atmosphere.

    Planned
  5. 5.5
    The complex cell

    Endosymbiosis and the origin of the eukaryotic cell.

    Planned
  6. 5.6
    The Cambrian explosion

    Animal body plans appear in the fossil record.

    Planned
  7. 5.7
    Mass extinctions

    Five great dyings and the age of reptiles.

    Planned
  8. 5.8
    Mammals in the shadows

    How small mammals survived the dinosaurs and inherited the Earth.

    Draft

Disciplines