Notes: The Geologic Time Scale

1. Notes: The Geologic Time Scale Read pgs 286-297. Objective: Explain what happens at the beginning and end of each era. Video: Land Formation

2. Geologic Time Scale • Geologic Time Scale: the record of the life forms and geologic events in the Earth’s history. • Since the span of time is so great from the formation of the Earth to now, scientists can’t use a normal calendar to describe times.

3. Geologic Time Scale • The geologic time scale is broken into 4 eras. These are characterized by the type of animal that dominated that period of time. Video: Geologic Time Scale

4. Time on Earth

5. Reasons for Extinctions • Movements of continents. • Meteorites hitting the Earth. • Ice ages. • Major changes in the climate.

6. The Four Eras • Scientists have divided the geologic history into four eras. • Precambrian Time. • Paleozoic Era. • Mesozoic Era. • Cenozoic Era.

7. Precambrian Time • Precambrian Time: beginning of the Earth to 540 mya. • Means before Cambrian. Baicalia= bacteria

8. Dominant Life • Single-celled organims.

9. Major Events • Earth Forms about 4.6 bya. • Scientists hypothesize that Earth was a place of great turmoil. • Meteorites crashed into Earth. • Constant violent thunder storms. • Volcanic eruptions. • Intense radiation from the sun.

10. Major Events Video: Precambrian

11. Major Events • Scientists hypothesize that DNA-like molecules developed in the oceans from nonliving matter that already existed. This matter included water, clay, minerals in the ocean and gases in the atmosphere. The energy present in the early Earth caused these chemicals to react and form DNA like material.

12. Major Events • For millions of years DNA like molecules floated in the oceans reacting with each other to make more complex molecules.

13. Major Events • The reactions of these molecules may have led to the first prokaryotic cells evolve about 3.5 bya.

14. Major Events Bacteria

15. Major Events • Early life did not need oxygen to survive, they were anaerobic. They made their own food from carbon dioxide through photosynthesis and gave off oxygen as waste.

16. Major Events • As the atmosphere took on more oxygen, it formed a shield to protect Earth from the sun’s rays called the ozone layer. This helped keep oxygen in the air and allowed early life to evolve to breathe the oxygen in the air. These new organisms are now called eukaryotes, or cells with a nucleus.

17. Major Events • The first eukaryotes evolved over 2 billion years ago, as a result of extra oxygen in the atmosphere. Nucleus Prokaryote Eukaryote

18. Major Events • By the end of Precambrian Era, simple multi-celled organisms evolved.

19. Paleozoic Era • Paleozoic Era: 540mya-248mya, means “ancient life”. • Rocks from this era are rich in fossils of animals such as sponges, corals, snails, clams, squids, trilobites, and early fish and sharks.

20. Dominant Life • Amphibians and primitive land plants.

21. Major Events • The Paleozoic era begins with the Cambrian Explosion, a major burst of evolution. • The Cambrian Explosion was a time of a great number of new species evolving.

22. Major Events • Fish and diverse marine life evolve. Snails Corals Sponges Clams Squids Trilobites Video: Paleozoic Era

23. Major Events • During the Paleozoic Era, plants, fungi, and air-breathing animals colonized dry land. • Plants provided the first land animals with food and shelter. Giant Ferns Conifers Horsetails

24. Major Events • Fossils indicate that crawling insects were some of the first land animals. • Near the end of the era, reptiles, winged insects, cockroaches, and dragonflies appeared. Dragonflies Reptiles Cockroaches

25. Major Events • The Permian Extinction: The largest mass extinction known occurred at the end of the Paleozoic era, about 90% of all marine species died out. Video: Ice Age

26. Mesozoic Era • Mesozoic Era: 248mya-65mya, means “middle life”, also called the age of reptiles. • After the Paleozoic mass extinction scientists think there was a burst of evolution resulting in many new and different species. Video: Mesozoic Era

27. Dominant Life • Reptiles and coniferous plants.

28. Major Events • Reptiles, coniferous plants, and palm trees dominate land.

29. Major Events • Dinosaurs, birds, and flowering plants evolve. Birds Dinosaurs Flowers

30. Major Events • Small mammals evolved probably from warm blooded reptiles.

31. Major Events • K-T Extinction: At the end of the Mesozoic era, an asteroid is believed to have hit the earth causing a mass extinction. • It is believed a large asteroid hit the Earth, caused dust to block the sun killing all of the plants, the animals had nothing to eat so they died. Temperatures also dropped very low. Song: Do The Dinosaur

32. Poor Dinosaurs Video: Extinction

33. Cenozoic Era • Cenozoic Era: 65mya-now, means “recent life”, also called the age of mammals. • We have the most fossil information from this era because the fossils from this era are closest to the surface. Video: Cenozoic Era

34. Dominant Life • Mammals and flowering plants.

35. Cenozoic Life Saber-toothed Cat Camels Mastodon and Cro-Magnon man

36. Major Events • Most fossils evidence from this era.

37. Major Events • Mammals, flowering plants, and insects dominate land.

38. Major Events • The evolution of humans begins it’s journey from early primates to modern humans.

39. Major Events • Modern humans or Homo sapiens may have evolved as early as 200,000 years ago.