The document summarizes the major divisions of geologic time including eras, periods, and epochs. It describes the key events and life forms that characterized each era from the Precambrian to the present-day Cenozoic era. Major points of discussion include the formation and breakup of supercontinents like Rodinia and Pangaea, as well as major extinction events like the one that wiped out the dinosaurs.

1. Divisions of Geologic Time
• Eras are subdivided into periods...periods
are subdivided into epochs.
Era
Period
Epoch
E + P = EP

2. 4 -Eras
4. Cenozoic (recent life)
– 65 Ma through present day
3. Mesozoic (middle life)
– 250 Ma…lasted 180 Ma
2. Paleozoic (ancient life)
– 542 Ma…lasted 300 Ma
1. Precambrian/Azoic – 88% of earth’s history
Entire time before 542 Ma (542-4600 Ma)

3. Major events in different Eras

4. Heard of Pangaea?
the supercontinent that included all
continents on Earth.
It began to break apart c. 175 Ma.

5. But before Pangaea, Earth’s landmasses
ripped apart and smashed back together to
form supercontinents repeatedly.
This cycle has been going on for the last 3.0
Ga.- regulating our planet’s geography,
climate, and carbon cycles.

6. Rodinia
900 Ma

7. Paleozoic Era
begins with the breakup of the Rodinia.

8. The beginning of Paleozoic Era
Cambrian (542-485 Ma)
Named after Cambria, the Roman name for
Wales, where Adam Sedgwick, one of the
pioneers of geology, studied rock strata.
Charles Darwin was one of his students.
(Sedgwick, however, never
accepted Darwin's theory of evolution and
natural selection.)

9. Life in Paleozoic
• Explosion of life in the oceans began during this era.
The Cambrian Period (542-485 Ma) is the “Age of the Trilobites”
• Most of the continents were covered in warm, shallow seas.
– Invertebrates dominant – Trilobites, Brachiopods
– Fish emerged
– Early land plants including mosses, ferns and cone-bearing
plants.
– The early coal forming forests were also formed during this
time.
– Fish led to the arrival of amphibians
The Carboniferous Period (360-300 Ma) is called the “Age
of Amphibians”

10. Trilobites
• Lived in Earth’s ancient seas
• Extinct before the dinosaurs
came into existence
• Cambrian Period is know as
the “Age of the Trilobites”

11. Brachiopods
• Marine animals that resemble clams.

12. Early Fish
Early fish had no jaws
Cambrian Sea monster
(National Geographic)

13. Early Land Plants
Cone bearing plants
Ferns
Mosses

14. The Appalachian mountains were formed during
Paleozoic (480 Ma- Ordovician Period).
Major tectonic event during Paleozoic

15. End of Paleozoic Era
• Paleozoic closed with the formation of Pangaea,
as the Earth's continents came together once
again.

16. The end of Paleozoic Era
• largest mass extinction in history wiped out
approximately 90% of all marine animal species
and 70% of land animals.
– Possible causes of this Mass Extinction Event
• Lowering of sea levels when the continents were
rejoined as Pangaea (convergent boundary)
• Increased volcanic activity (ash and dust)
• Climate changes – cooler climate

17. Mesozoic Era – Middle Life
• At the beginning of this era the continents
were joined as Pangaea.
• Pangaea broke up around the middle of
this era.

18. Mesozoic Era
• Reptiles: Most abundant because of their
ability to adapt to the drier climate.
• Dinosaurs:
– First small dinosaurs appeared in the Triassic
Larger and more abundant dinosaurs
appeared in the Jurassic Period.
• Small mammals and birds also appeared
during this era.
– The mammals were small, warm-blooded
animals. Hair covering their bodies.

21. Mesozoic Mammals

23. Mesozoic Plants
Flowering plants evolved
towards the end of the
Mesozoic Era.

24. End of Mesozoic Era
• Mass extinction event about 65 million years
ago.
– Many groups of animals, including the dinosaurs
disappeared suddenly at this time.
• Many scientists believe that this event was
caused by a comet or asteroid colliding with the
Earth.

25. End of Mesozoic Era
Mass Extinction Event
• Asteroid or Comet collides with Earth.
– Huge cloud of smoke and dust fills the air
– Blocks out sunlight
– Plants die
– Animals that eat plants die
– Animals that eat plant-eaters die.
• However, not all forms of life were extinct.
• Many animals today are descendants from
the survivors of this extinction event.

26. Cenozoic Era – Recent Life
• Began about 65 million years ago and continues
today
– Climate was warm and mild.
– Marine animals such as whales and dolphins evolved.
• Mammals began to increase and evolve adaptations
that allowed them to live in many different
environments – land, air and the sea.
– Grasses increased and provided a food source for grazing
animals
• Many mountain ranges were formed:
– Alps in Europe; Himalaya in India; Rocky Mountains in
the USA

27. Tectonics in Cenozoic
Himalaya, Alps
https://www.edumedia-sciences.com/en/media/565-formation-of-the-himalayas
Alps (34-24 Ma)
Oligocene-Miocene

28. Cenozoic Era
• Growth of these mountains may have helped to
cool down the climate
– Ice Ages occurred late in the Cenozoic Era
(Quaternary Period).
• As the climate changed, the animals had to
adapt to the rise and fall of the oceans caused
by melting glaciers.
• This era is sometimes called the “Age of
Mammals”

29. Cenozoic Era
• Marine animal examples:
– Algae, Molluscs, Fish and Mammals
• Land animal examples:
– Bats, Cats, Dogs, Cattle and Humans
– Humans are thought to have appeared around 3.5
million years ago (during the most recent period –
Quaternary).
• Flowering plants were now the most common
plant life.

30. Cenozoic Mammals

31. Flowering Plants were common
during the Cenozoic Era

32. Today
• Today we are in the Holocene Epoch of
the Quaternary Period of the Cenozoic
Era.
Which unit is the largest?
Which unit is the smallest?