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3 - 2.4
2.4 - 1.8
1.8 - 1.2
1.2 - 600 Million
600 - 0
3 - 0 B
13th GY
3 - 2.75
12th GY
2.75 - 2.5
11th GY
2.5 - 2.25
10th GY
2.25 - 2
9th GY
2 - 1.75
8th GY
2 - 1.75
7th GY
1.75 - 1.5
6th GY
1.5 - 1.75
5th GY
1.25 - 1
4th GY
1 B - 750 M
3rd GY
750 - 500
2nd GY
500 - 250
1st GY
250 - Pr
Precambrian Time 4.5 - 543 M
Mesoproterozoic 1.6 B - 900
Neoproterozoic 900 - 543
Archean Eon 3.9 - 2.5
Proterozoic Eon 2.5 - 540 M
Phanerozoic Era 543 - Present
Vendian 650 - 543
Archean Eon 3.9 - 2.5
Geologic - The Earth's permanent crust is formed. Vast amounts of metallic minerals are deposited. The oceans and atmosphere result from volcanic outgassing.
Biologic - The earliest life forms evolve in the seas. They are the prokaryotes—single-celled organisms with no nucleus—cyanobacteria (blue-green algae). The earliest bacteria obtain energy through chemosynthesis (ingestion of organic molecules).
- 2.5 First organisms to utilize oxygen.
- 2.1 More complex cells appear: Eukaryotes, which contain various organelles. The eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells. The origin of the eukaryotic cell is a milestone in the evolution of life. Their higher level of organizational complexity permits the development of truly multicellular organisms.
- 900 - 543 Neoproterozoic
Mesoproterozoic 1.6 B - 900
Geologic - The supercontinent Rodinia forms approximately 1.1 billion years ago. Plate tectonics slows to approximately the same rate as the present. Large mountain chains form as the continents collide. Quartz-rich sandstones, shales, and limestones are deposited over the continents. Oxygen levels increase as life on Earth develops the ability to obtain energy through photosynthesis. The late Proterozoic is an "Ice House" world.
Biologic - Eukaryotes (single-celled organisms with a nucleus) evolve. These are more advanced forms of algae and a wide variety of protozoa. Eukaryotes can reproduce sexually, which makes genetic diversity possible, as well as the ability to adapt to and survive environmental changes. Multi-celled, soft-bodied marine organisms (metazoans) evolve.
- 1.2 Sexual reproduction evolves, leading to faster evolution.
- 900 Choanoflagellates are considered ancestors of the entire animal kingdom, and in particular may be the direct ancestors of sponges.
The choanocytes (collar cells) of sponges have the same basic structure as choanoflagellates. Collar cells are occasionally found in a few other animal groups, such as flatworms. Comparisons of DNA sequences support a close affiliation between choanoflagellates and animals.
- 850 Proterospongia (members of the Choanoflagellata) are the best living examples of what the ancestor of all animals may have looked like.
They live in colonies, and show a primitive level of cellular specialization for different tasks.
The similarities between Proterospongia and sponges are strong evidence for the close relationship between protozoans and metazoans.
- 650 - 543 Vendian
- 600 It is thought that the earliest multicellular life on Earth was a sponge-like creature.
Sponges are among the simplest of animals, with partially differentiated tissues but without muscles, nerves, or internal organs.
Sponges ( Porifera) are the phylogenetically oldest animal phylum extant today.
In some ways they are closer to being cell colonies than multicellular organisms.
- 543 - 248 Paleozoic Era (Ancient Life)
- 248 - 65 Mesozoic Era (Middle Life)
- 65 - Present Cenozoic Era
- 543 - Present Phanerozoic Era
- 530 - 527 Tommotian
Carboniferous Period 354 - 290
Geologic - Sedimentary rocks (sandstone, shale, limestone, conglomerate) form in shallow seas over the continents. Rodinia begins to break up into northern and southern portions. Gondwana in the south incorporates South America, Africa, Antarctica, and Western Australia as well as peninsular India and parts of Arabia.
The global climate is generally mild.
Biologic - The first fish, corals, trilobites and shellfish appeared.
Marine metazoans with mineralized skeletons, such as sponges, bryozoans, corals, brachiopods, molluscs, arthropods, and echinoderms, flourish. One group of arthropods, the trilobites, are particularly dominant in the shallow-water marine habitats.
Plant life is limited to marine algae.
- 250 Million to present 1st Galactic year