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LECTURE 1:
THE CALENDAR OF LIFE ON EARTH
The basic timeline is a 4.6 billion year old Earth, with (very
approximately):
- 4 billion years of simple
cells (prokaryotes),
- 3 billion years of photosynthesis,
- 2 billion years of complex
cells (eukaryotes),
- 1 billion years of multicellular life,
- 600 million years of simple animals,
- 570 million years of arthropods (ancestors of insects, arachnids and
crustaceans)
- 550 million years of complex animals
- 500 million years of fish and
proto-amphibians,
- 475 million years of land plants,
- 400 million years of insects and seeds,
- 360 million years of amphibians,
- 300 million years of reptiles,
- 200 million years of mammals,
- 150 million years of birds,
- 130 million years of flowers,
- 65 million years since the non-avian dinosaurs died out,
- 200,000 years since humans started looking like they do today.
| 4567.17 Ma |
The planet Earth forms from the accretion disc revolving
around the young Sun. |
| 4533 Ma |
The planet Earth and the planet Theia collide, sending countless moonlets
into orbit around the young Earth. These moonlets eventually coalesce to form
the Moon. The gravitational pull of the new
Moon stabilises the Earth's fluctuating axis of rotation and
sets up the conditions for the formation of life.[1] |
| 4100 Ma |
The surface of the Earth cools enough for the crust to solidify. The atmosphere and
the oceans form.[2]PAH infall,
and Iron-Sulfide
synthesis along deep ocean platelet boundaries, may have led to the RNA world of
competing metabolising organic compounds. |
| 4500 - 2500 Ma |
The earliest life appears, possibly derived from self-reproducing RNA molecules. The replication of these organisms requires
resources like energy, space, and smaller building blocks, which soon become
limited, resulting in competition. Natural selection favours those molecules
which are more efficient at replication. DNA
molecules then take over as the main replicators. They soon develop inside
enclosing membranes which provide a stable physical and chemical environment
conducive to their replication: proto-cells. |
| 3900 Ma |
Late
Heavy Bombardment: peak rate of impact events upon the inner planets by meteors.
This constant disturbance
probably obliterated any life that had already evolved, as the oceans boiled
away completely; conversely, life may have been transported to Earth by a meteor. [3] |
| 3900 - 2500 Ma |
Cells
resembling prokaryotes appear.
These first organisms are chemoautotrophs: they use carbon dioxide as a carbon source and oxidize inorganic materials to extract energy. Later,
prokaryotes evolve glycolysis, a
set of chemical reactions that free the energy of organic molecules such as glucose. Glycolysis generates ATP
molecules as short-term energy currency, and ATP continue to be used in almost
all organisms, unchanged, to this day. |
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Prof. Torgersen
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