The History of Life on Earth Earth
Contents:

Timeline of Life on Earth and it's Atmosphere




Time Characteristics Name of Stage Duration of Stage (Billions of Years Ago) Chemicals/Gases in Atmosphere Important Processes and Features

4.5 billion years

Formation of the approximately homogeneous solid Earth by planetesimal accretion.

Early Atmosphere 4.4 to 4.0 H2O, hydrogen cyanide (HCN),
ammonia (NH3),
methane (CH4),
sulfur, iodine, bromine, chlorine, argon
Lighter gases like hydrogen and helium escaped to space. All water was held in the atmosphere as vapor because of high temperatures.

4.0 billion years

Planet surface cools and bombardment from space slows, so life has the possibility of existing on the planet. Oldest earth rocks dated by radioactivity.

Secondary Atmosphere 4.0 to 3.3 At 4.0 billion H2O, CO2, and nitrogen (N) were the dominant chemicals. Cooling of the atmosphere causes precipitation and the development of the oceans. By 3.0 billion CO2, H2O, N2 are the dominant chemicals. O2 begins to accumulate. Continued release of gases from the lithosphere. Water vapor clouds were common in the lower atmosphere. Chemosynthetic bacteria appear on the Earth at 3.6 billion. Life begins to modify the atmosphere.

3.85 billion years

Evidence for life seen in Greenland rocks enriched in C12 isotope.

3.85 - 3.7 billion years

Prokaryotes diverge from Archaea. Sometime after prokaryotes diverge from archaea, chlorophyll and photosynthesis evolve in the bacterial lineage. Archaea do not make chlorophyll, and only some bacteria are photosynthetic.

3.7 billion years

First banded iron formation seen. Implies oxygen made by photosynthesis.

3.5 billion years

First stromatolites seen (assumed to be of biological origin, with cyanobacteria, as in present day stromatolites).

3.5 - 2.8 billion years

Beginning of photosynthesis by blue-green algae which releases oxygen molecules into the atmosphere and steadily works to strengthen the ozone layer and change the Earth's chemically reducing atmosphere into a chemically oxidizing one.

Living Atmosphere 3.3 to Present N2, O2, Argon, CO2 Development, evolution and growth of life increase the quantity of oxygen in the atmosphere. Concentration of atmospheric oxygen levels off. Starting about year 1700, humans begin to modify the concentrations of some gases in the atmosphere

2.7 billion years

Steranes = eukaryotic sterol derived biomarkers found in Australian shale.

2.4 billion years

Rise in the concentration of oxygen molecules stops the deposition of uraninites (since they are soluble when combined with oxygen).

2.1 million years

First tentative evidence of a eukaryotic microfossil, not yet confirmed.

2.0 billion years

Oxygen begins to rise in the atmosphere after oxygen sinks saturated. The Oklo natural fission reactor in Gabon goes into operation.

1.6 billion years

The last reserves of reduced iron are used up by the increasing atmospheric oxygen--last banded iron formations.

1.5 billion years

Oxygen level in the atmosphere reaches present day level and stabilizes. Chloroplasts and mitochondria present. Eukaryotic cell organisms develop.

1.2 billion years

Major eukaryotic groups diverge. Plants separate before animals/fungi.

670 million years

Invertebrates and vertebrates diverge.

1500 - 600 million years

Rise of multicellular organisms.

580 - 545 million years

Fossils of Ediacaran organisms are made.

530 million years

Cambrian explosion of fossil record. Burgess shale.

528 - 526 million years

Fossilization of the Chengjiang site.

500 - 450 million years

Rise of the fish--first vertebrates.

430 million years

Waxy coated algae begin to live on land.

420 million years

Millipedes have evolved-first land animals.

380 million years

Vertebrates move onto land.

375 million years

Appearance of primitive sharks.

360 million years

Gymnosperms (naked seed plants) diverge from angiosperms (flowering plants).

350 million years

Primitive insects have evolved and primitive ferns evolve-first plants with roots.

310 million years

Birds and other vertebrates diverge.

350-300 million years

Rise of the amphibians.

300 million years

Winged insects have evolved.

280 million years

Beetles and weevils have evolved.

230 million years

Roaches and termites have evolved.

225 million years

Modern ferns have evolved and Bbees have evolved.

300 - 200 million years

Rise of the reptiles

200 million years

Pangaea starts to break apart, primitive crocodiles have evolved and appearance of mammals

200 - 150 million years

Monocots diverge from dicots, oldest angiosperm fossil = 142 million years

145 million years

Archaeopteryx walks the Earth

150 - 90 million years

Primitive kangaroos, cranes and modern sharks have evolved.

65 million years

K-T Boundary--extinction of the dinosaurs and beginning of the reign of mammals

7 - 6 million years

Sahelanthropus tchadensis - oldest known hominid or near-hominid species

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