The document summarizes the major periods of life on Earth from the Precambrian Era to present day. It describes five major mass extinctions that occurred over this time span. Key events included the Cambrian Explosion of complex life around 540 million years ago, the rise and dominance of dinosaurs in the Mesozoic Era before their extinction 66 million years ago, and the evolution of modern humans in the Quaternary Period beginning around 2 million years ago. The document uses fossils and geological evidence to reconstruct the history of life on our planet over the past 4.5 billion years.

1. Life on Earth
Anuradha Malalasena

2. Fossils
• History of earth is written on fossils.
• What we know today is, how scientist interpret it.
• How fossils survived millions of years?

3. Mass Extinction
• More than 90 percent of all organisms that have ever lived on Earth
are extinct.
• When at least half of all species die out in a relatively short time, we
call it mass extinction.
• Top five extinctions
• Ordovician Extinction – 86% (440 mya)
• Devonian Extinction – 75% (365 mya)
• Permian Extinction – 96% (250 mya)
• Triassic Extinction – 80% (210 mya)
• Cretaceous Extinction – 76% (65 mya)

4. Precambrian Era
• Starts with the formation of Earth about 4.5 billion years ago
and ends at the first sign of complex life about 540 million
years ago.
• The Precambrian covers almost 90% of the entire history of
the Earth.
• The Precambrian has been divided into three ages:
• The Hadean
• The Archean
• The Proterozoic.

5. Paleozoic Era
• Ran from 542 MYA to 251 MYA
• The Paleozoic was a time of dramatic geological, climatic, and
evolutionary change.
• 3 major mass extinction happened
• Paleozoic era has been divided into six ages.
• Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.

6. Cambrian Era
• This period lasted about 53 million years and marked a dramatic burst
of evolutionary changes in life on Earth, known as the "Cambrian
Explosion.“
• Hard shell sea creature start to become common
• Earliest almost-vertebrates marine organisms also evolved

7. Anomalocaris

8. Graptolites

9. Ordovician Era
• The Ordovician spans 41.2 million years from the end of the Cambrian
Period.
• Started and ended with two mass extinctions
• Many type of fish evolved along with invertebrates

10. Trilobites

11. Sacabambaspis (a jawless fish)

12. Silurian Era
• The Silurian Period occurred from 443 MYA to 416 MYA.
• Warm and stable climate
• First simple plants to colonize the land

14. Devonian Era
• Spanning 60 million years from the end of the Silurian, 419.2 MYA to
358.9 MYA
• Many type of fish evolved
• Some crawled out of the water and became first amphibians.

15. Tiktaalik (Walking Fish)

16. Carboniferous Era
• The Carboniferous Period lasted from about 359.2 to 299 million
years ago
• This period is famous for its vast swamp forests
• Covered with early tree like, ferns/horsetails/ mosses
• Some trees were more than 30m tall
• Spiders and Insects evolved
• They were hunted by large amphibians

18. Permian Era
• The Permian period lasted from 299 to 251 million years ago.
• The emerging supercontinent of Pangaea presented extremes of
climate and environment.
• The swamp forests were gradually replaced drought-resistant plants.
• Early reptiles were well placed to capitalize on the new environment,
shielded by their thicker, moisture-retaining skins

19. Dimetrodon

20. Permian Era
• Being cold-blooded, reptiles had to deal with big daily variations in
temperature.
• Freezing at night and over 38 degrees during the day
• Some of the reptiles had sail-like structures on their backs
• Mammals evolved from reptiles
• Permian ended with the largest mass extinction recorded in the
history of life on Earth

21. Permian Extinction
• Scientist believes that the Permian extinction was caused by acid rain
following a massive release of volcanic gases.
• It took 30 million years to recover from the extinction
• Two groups of animals survived the Permian Extinction
• Therapsids, which were mammal-like reptiles
• The more reptilian Archosaurs.

22. Mesozoic Era
• The Mesozoic Era began 252 MYA and ended 66 MYA.
• The Mesozoic is divided into three time periods
• Triassic
• Jurassic
• Cretaceous

23. Triassic Era
• The first period of the Mesozoic Era and occurred between 251 MYA
and 199 MYA.
• The oceans were massively depopulated and group of reptiles
returned back to the ocean.
• By mid of Triassic, most of the Therapsids had become extinct
reptilian Archosaurs were dominant.

24. Triassic Era
• Some Archosaurs evolved into true dinosaurs by the mid-Triassic.
• By the late Triassic, a group of Archosaurs had branched into the
flying dinosaurs.
• The first mammals evolved near the end of the Triassic Period from
the nearly extinct Therapsids.

25. Sharovipteryx

26. Brasilodontidae

27. Jurassic Era
• The Jurassic Period was the second segment of the Mesozoic Era. It
occurred from 199.6 to 145.5 MYA
• The supercontinent Pangaea split apart.
• On land, dinosaurs were making their mark in a big way.
• The earliest known bird, Archaeopteryx, took to the skies in the late
Jurassic.

28. Brachiosaurus

29. Allosaurus

30. Cretaceous Era
• Spans 79 million years from end of Jurassic Period (145 – 66 MYA)
• Oceans formed as land shifted and broke out of one big
supercontinent into smaller ones
• First flowering plants appeared on earth.
• Herd-dwelling Iguanodon spread everywhere but Antarctica.
• Tyrannosaurus rex dominated the late Cretaceous in the north.
• Monstrous meat-eaters like Spinosaurus, thrived in the south.

31. Tyrannosaurus

33. Cretaceous Mass Extinction
• The Cretaceous mass extinction is well-known for the death of the
dinosaurs.
• It killed off all dinosaurs except Birds
• Happened 66 MYA

34. Cenozoic Era
• Following the Mesozoic Era and, extending from 66 million years ago
to the present day
• Divided into 3 time periods
• Paleogene
• Neogene
• Quaternary

35. Paleogene Era
• Span from 66MYA to 23MYA
• Gigantic Dinosaur are gone.
• Fish filled in the oceans, food to fuel sharks.
• Biggest development in the seas was the appearance of whales.
• Mammals started evolve, they grow bigger

36. Neogene Era
• The Neogene Period encompasses the interval between 23 MYA and
2.6 MYA.
• Mountains rose, and sea levels fell.
• Hominins split from their closest African ape ancestors, the
chimpanzees.
• Adapted to two-footed walking.

37. Quaternary Era
• 2.3MYA to Present
• World entered a long ice age.
• Modern human evolved in Africa and spread word wide.

38. What if Earth existed for only 24 hours ??
https://www.youtube.com/watch?v=jtNs5k2KHXU

39. Thank You !