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GEOLOGICAL TIMELINE EVENTS
PRECAMBRIAN TIME (4.6 BYA – 540 MYA)
 During the Precambrian rock solidified, the oceans formed, and the first prokaryotes appeared.
 Represents 85% of geological time.
 Few fossils exist from this time because the animals were all soft-bodied.
 Life existed only in the sea
PRECAMBRIAN TIME (4.6 BYA – 540 MYA)
 4.6 BYA Formation of the Earth and Moon
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Many volcanic eruptions and asteroid collisions.
 3.5 BYA Prokaryotic bacteria flourished in the warm shallow seas.
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Evidence for this found in structures called stromatolite.
 2.4 BYA Oxygen level rise to 2%
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Cyanobacteria evolved approximately 2.6 bya.
 1.8 BYA First Eukaryotes
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Lichens may have been found on terrestrial rock surface as early as 600 mya. Lichen is a mutualistic symbiotic relationship
between a fungus and photosynthetic bacteria. Lichen produces acids that breakdown rocks to release minerals for their
own use. Liken is an important player in soil formation, however this soil was nutrient poor and could not sustain life.
Life existed only in the sea
PALEOZOIC TIME (541 MYA – 252 MYA)
 The Paleozoic Time is broken down into 4 Periods: Cambrian, Ordovician, Silurian, Devonian,
Carboniferous and Permian.
PALEOZOIC TIME (541 MYA – 252 MYA)
 Cambrian Period
 First fish appear
 End of the Ordovician Extinction (marine life including trilobites)
 For the first time, many organisms had hard shells and outer skeletons.
 Invertebrates, such as jellyfishes, worms and sponges.
 Brachiopods, small animals with two shells.
 Trilobites, arthropods which are invertebrates with segmented bodies, jointed limbs, and external skeletons.
 Ordovician and Silurian Period
 Ancestors of modern octopi and squid appeared.
 Aquatic arthropods.
 Some of them became the first animals to live on land.
 First land plants evolved from aquatic ancestors.
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Volcanic eruptions during this time, produced nutrient rich soils that allowed plants to evolve on land.
PALEOZOIC TIME (541 MYA – 252 MYA)
 Devonian Period
 Age of Fishes
 Some plants such as ferns, had adapted to drier areas.
 Insects, which are arthropods, appeared on land.
 Vertebrates began to invade the land.
 Early four-legged vertebrates evolved into amphibians. Amphibians live part of their life on land and part of its life in
water.
 Late Devonian Extinction (70% marine life perished)
PALEOZOIC TIME (541 MYA – 252 MYA)
 Carboniferous and Permian Period
 Reptiles evolved from amphibians.
 Swampy forests were formed from giant ferns and other plants.
 Remains of those ancient plants formed thick deposits of sediment that changed into coal over millions of
years.
 At the end of the Paleozoic, many organisms died out due to mass extinction.
 Mass extinction at the end of the Paleozoic affected both plants and animals on land and in the seas.
 As much as 90 percent of the complex life in the oceans disappeared.
 The mass extinction did not affect many fish. Many reptiles also survived.
MESOZOIC ERA (252 MYA – 66 MYA)
 Main events: Dominance of Dinosaurs, and appearance of flowering plants.
 Divided into 3 periods:Triassic, Jurassic and Cretaceous.
MESOZOIC ERA (252 MYA – 66 MYA)
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Triassic Period
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Age of reptiles.
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First dinosaurs appeared 225 million years ago.
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Mammals also first appeared.
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Important organisms in this new ecosystem were:
 fishes
 insects
 reptiles
 Cone bearing plants
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Jurassic Period
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Dinosaurs became the dominant animals on land.
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One of the first birds, called Archeopteryx appeared.
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Birds are close relatives of dinosaurs.
MESOZOIC ERA (252 MYA – 66 MYA)
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Cretaceous Period
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Reptiles were still the dominant vertebrates.
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Dinosaurs such as T Rex dominated the land ecosystem.
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Sea life forms:
 Turtles
 Crocodiles
 Extinct reptiles
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New life forms:
 Leafy trees, shrubs and small flowering plants.
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Another mass extinction. More than half of all plants and animal groups were wiped out, including Dinosaurs.
CENOZOIC ERA (241MYA TO PRESENT)
 Mammals evolved adaptations that allowed them to live in various environments such as:
 on land
 water
 air
 Age of Mammals.
CENOZOIC (241MYA TO PRESENT)
 Tertiary Period
 Earth’s climate was warm and mild.
 Marine mammals such as whales and dolphins evolved.
 Evolution of grazing mammals.
 Quaternary Period
 Earth’s climate cooled causing a series of ice ages.
 Organisms that thrived in the oceans:
 Algae, coral, mollusks, fishes, mammals.
 The first fossil to our own species, Homo sapiens, may have appeared as early as 3.200.000 years ago in
Africa.