1. Geologic Time
ES Chapter 11

2. Units of Geologic Time Earth is 4.6 billion years old
Need to split up to make sense
Periods are the basic unit
Single rock system forms, often there is a mass extinction
Era
2 or more periods
Represent major changes in the fossil record
End with a mass extinction
Eon
2 or more eras

3. Geologic Timeline The eras and periods are not equal in length
Defined based on events
Periods are further divided into epochs
Not discussing in this class…

4. Hadean Eon (Precambrian)
4.6 bya-4 bya
Formation of earth to solidification of rocks
No geologic record because no rocks
Named after Hades
“Hellish”
Very hot
A lot of volcanic eruptions
Lava covering much of the surface
A lot of collisions with space debris left over from planetary nebula

5. Formation of the moon (more to come later)
Hadean Eon
Likely due to collision between young earth and a large rocky object

6. Archean Eon (Precambrian)
4 bya-2.5bya
Formation of the crust-first photosynthetic organisms
Still very hot
Atmosphere was mostly volcanic gases
Little breathable oxygen, a lot of carbon dioxide
Single-celled life formed near beginning and existed throughout

7. Proterozoic Eon (Precambrian)
2.5 bya-542 mya
Oxygen becoming abundant-Cambrian explosion
Geologic processes released oxygen
Glaciation events
Plate tectonics and supercontinent formation
Evolution of eukaryotes and multicellular organisms
Most had soft bodies
Many existed for a short time, then went extinct

8. Evolution and Extinction in Geologic Record
Evolution-Change in the traits in a population over time
1 species may split into 2 if they are reproductively separated
Geographic isolation-populations of organisms becoming split due to geologic processes
Tectonic plates provided a lot of geologic isolation
Land bridges (a piece of land separating 2 previously isolated continents
Evolution is driven by changing environments
When conditions change, organisms can adapt, migrate, or they will die
Extinction is the death of the last member of a species
Mass extinctions occur when many species go extinct in a short geologic time (no more than a couple million years)

9. Phanerozoic Eon Current geologic eon (542mya-present)
Life as we know it evolved (complex plants, fish, tetrapods, insects, dinosaurs, etc.)
Formation and breaking-up of Pangea
Eventual evolution of humans
3 eras distinguished by mass extinctions
All end with “zoic” which comes from “zoe” meaning “life”
12 periods (11 in book. 1 has recently been split into 2)

10. Phanerozoic Eon-Paleozoic Era
Longest era in Phanerozoic Eon
542 mya-251 mya
Age of invertebrates
6 periods

11. Cambrian Period 542-468 mya Cambrian Explosion Still no life on land
“Sudden” evolution of many complex organisms in water
Happened over a period of about 100 million years
Huge amount of diversity for the first time on Earth
Some were similar to current life
Cnidarians, mollusks, etc.
Likely due to increase in oxygen levels (photosynthetic organisms), stabilization of temperatures, and decreased volcanism
Still no life on land
Earth was cool

15. Ordovician Period 488-444 mya A lot of invertebrates
Began with Cambrian-Ordovician mass extinction
Killed many trilobite species, along with others
Ended with Ordovician-Silurian mass extinction
Killed 50-60% of the species
A lot of invertebrates
Still no organisms on land
Evolution continued, new species formed
Mountain building and volcanic arcs
Including Appalachian Mountains

17. Silurian Period 444-416 mya Earth warmed, glaciers melted
Began with O-S mass extinction
Ended with the aptly named End-Silurian mass extinction
Earth warmed, glaciers melted
Evolution of fish and terrestrial plants
Also allowed some arthropods to leave the water

18. Devonian period 419-359 mya Age of the Fish
Began with End-Silurian mass extinction
Ended with Late Devonian mass extinction
Mostly killed off trilobites
Age of the Fish
Included Tiktaalik, the ancestor to tetrapods (4-limbed organisms)
A lot of organisms evolving on land
Plants probably began causing land to green
Soils beginning to form
Coral reefs were common

19. Tiktaalik Video

20. Carboniferous Period 359-399 mya A lot of swampy forests
Began at Late Devonian mass extinction
Ended at the formation of Pangea
A lot of swampy forests
A lot of fossil fuels formed in this period
Reptile evolved and became wide-spread
Arthropods similar to those today, though much larger, evolved
Dragonflys, 8-foot-long millipedes and centipedes (horrifying!)

21. Permian Period
mya
Began at formation of Pangea
Ended with a mass extinction that killed about 96% of all species
Largest in Earth’s history, nearly wiped life out forever
Ended the Paleozoic Era and the age of invertebrates
Evolution of mammals, early alligators/crocodiles, turtles, and some large reptiles

22. Permian Period Video

23. The Mesozoic Era 251-65.5 mya The age of the dinosaurs
3 periods (most familiar to you)
Triassic Period
Jurassic Period
Cretaceous Period

24. Triassic Period
mya
Began with Permian mass extinction
Ended with Triassic-Jurassic Extinction
Wiped out many organisms and allowed dinosaurs to dominate
Mammals and ancestors to birds and alligators dominated
Pangea began to split apart
Climate was mostly hot and dry
No coal in the beginning as life was still recovering from Permian mass extinction

25. Triassic Period Video

26. Jurassic Period 200-145 mya Large herbivorous dinosaurs were common
Began with Triassic-Jurassic mass extinction
Ended with a minor mass extinction which killed most stegosaurid and sauropod dinosaurs
Large herbivorous dinosaurs were common
Some were already evolving into birds
Not the dinosaurs you are most familiar with
They came in the Cretaceous Period

27. Very minor Swearing

28. Cretaceous Period 145-65.5 mya
Began with minor mass extinction
Made way for most dinosaurs you are most familiar with
Ended with Cretaceous-Paleogene mass extinction
Asteroid that killed all non avian dinosaurs
Plate movement led to North America beginning to form
T. rex, velociraptors, triceratops, pterodactyls, and many other dinosaurs dominated
Asteroid changed the climate and caused the extinction of 75% of organisms
Made way for evolution of small mammals that survived

30. Crateous Period vid

31. Cenozoic Era 65.5 mya-current The age of mammals
Began with the extinction of the dinosaurs
The age of mammals
Mostly small organisms survived the asteroid impact and climate change
They quickly diversified to become more like modern organisms
Earth became cooler, then stabilized
Was divided into 2 periods (Tertiary and Quaternary), but recently was split into 3
Paleogene
Neogene
Quaternary

32. Paleogene Period 65.5-23 mya India and Asia were colliding
Began with extinction of dinosaurs
Ended ?
India and Asia were colliding
Most continents were nearing their current locations
The first grasses evolved
Savannahs and prairies formed
Mammals were diversifying rapidly

33. Neogene Period
mya
Began ?
Ended with glaciation
Mammals, including close ancestors of humans, continued to evolve
North and South America connected, separating the Atlantic and Pacific Oceans
Current Ice Age began
Ice age-period of time when a large part of earth is covered in glaciers

34. Quaternary Period 2.5 mya-present
Continents were nearly where they now are
Mammoths, mastodons and saber-toothed cats went extinct
Large period of glaciation
All of the life around you evolved or already existed
Humans evolved about 200,000 years ago in Africa and spread using land bridges