Geo Time Scale

1. The Geologic Time
Scale
4.6 Billion Years of Earth History

4. What is the Earth’s time scale?
• The Geological time scale is a record of
the life forms and geological events in
Earth’s history.
• Scientists developed the time scale by
studying rock layers and fossils world
wide.
• Radioactive dating helped determine the
absolute divisions in the time scale.

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

7. Divisions of Geologic Time
• Geological time begins with Precambrian
Time. Precambrian time covers
approximately 88% of Earth’s history.

9. One Super Eon and Four Eras
• PRE-CAMBRIAN Super Eon – 88% of earth’s
history
• Paleozoic (ancient life)
– 544 million years ago…lasted 300 million yrs
• Mesozoic (middle life)
– 245 million years ago…lasted 180 million yrs
• Cenozoic (recent life)
– 65 million years ago…continues through present day

10. 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?

12. Paleozoic Era (Ancient Life)
• “The Age of Fish”
• Starts: Cambrian period is the 1st
period of the
Paleozoic Era.
• “Explosion” of life in the oceans began during this era.
• Most of the continents covered in warm, shallow seas.
– Invertebrates were dominant - Trilobites
– Fish emerged during this time
– Fish led to the arrival of amphibians
– Early land plants including mosses, ferns and cone-bearing
plants.
– The coal forming forests grew during this time
(Carboniferous Period)

13. Paleozoic Era Con’t
• The Appalachian mountains were formed during
this time.
• The formation of Pangaea, as the Earth's
continents came together once again.
• Ends: Permian Period
• the largest mass extinction in history wiped
out up to 97% of all life on Earth.
– 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

14. Trilobites
• Lived in Earths ancient seas
• Extinct before the dinosaurs
came into existence
• Cambrian Period is know as
the “Age of the Trilobites”

15. Eurypterids (New York State Fossil)
Giant Sea Scorpion- largest known arthropods to ever live

16. Brachiopods
• Marine animals that resemble bivalves
such as clams.

17. Early Fish
Early fish did not have jaws.
Some species of sharks
were in existence at this
time.

18. Frilled Shark that was found in Japan in January 2007. This shark was
considered a “living fossil”

19. Early Land Plants
Cone bearing plants
Ferns
Mosses

20. Mesozoic Era (Middle Life)
• “The Age of Reptiles”
• Start: Triassic Period
• Pangaea is still joined together, broke up
around the middle of this era.
• Reptiles became the most abundant
animals because of their ability to adapt to
the drier climate of the Mesozoic Era.
– Skin maintains body fluids
– Embryos live in shells

21. Mesozoic Era
• Dinosaurs were very active in this era.
– First small dinosaurs appeared in the Triassic
Period.
– 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.
• These characteristics help them survive in
changing environments.

23. Mesozoic Era
• The main plant life of this time were
Gymnosperms or plants that produce seeds,
but no flowers.
– Pine Trees
• Flowering plants appeared during the END of
this era.
• End: Cretaceous Period
• This era ended with a mass extinction event
about 65 million years ago.
– Many groups of animals, including the dinosaurs
disappeared suddenly at this time.

25. Mesozoic Reptiles

26. Mesozoic Mammals

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

28. Cenozoic Era (Modern Life)
• “Age of Mammals”
• Start: Paleocene Period
• Starts 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 formed during the Cenozoic
Era
– Alps in Europe and Himalayas in India; Rocky Mountains in
the USA

29. Cenozoic Era
• 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.
• Marine animal examples:
– Algae, Mollusks, Fish and Mammals
• Land animal examples:
• Bats, Cats, Dogs, Cattle and Humans
• End: ??? TBD

30. Cenozoic Mammals

31. Flowering Plants were common
during the Cenozoic Era