The document summarizes the geological time scale which divides Earth's history into different eras, periods, and epochs based on fossil and stratigraphic evidence. It describes the four eons of Earth's history starting with the Hadean and Archean eons of the earliest lifeforms like bacteria. It then outlines the major eras - Paleozoic, Mesozoic, and Cenozoic - describing some of the significant lifeforms, events, and environmental changes that occurred during each period within these eras. The largest unit of the geological time scale is the eon, while the smallest is the epoch.

1. Geological Time Scale

2. 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.
• Geologic time scale provides a system of
chronologic measurement relating Stratigraphy to
time that is used by geologist, paleontologist and
other earth scientists.
• Used to describe the timing and relationship b/w
events that have occurred during the history of
earth.

3. • Scientists developed the time scale by studying
rock layers and fossils world wide.
• Radioactive dating helped determine the
absolute divisions in the time scale.
• Geologist qualify the units as early, middle and
late when referring to time, and lower, mid and
upper when referring to the corresponding rocks.

4. Division of Geologic Time Scale
• Earth history is subdivided into time units based on:
– The fossil record
– Extinctions

5. Four Eons
• Pre-Archean or Hadean (4.6 to 3.8 Billion years)
~4.6 BYA -- Formation of Earth and Moon
~4 BYA -- Likely origin of life
• Archean (3.8 to 2.5 Billion years)
The eon of first life
~3.8 BYA -- Oldest known rocks
~3.5 BYA -- Oldest known fossils (single celled organisms resembling bacteria)
3.2 BYA -- First known plants (algae)
• Proterozoic (2.5 Billion to 570 Million years)
The eon of the first multicelled life
1.2 BYA -- First known animal (jellyfish)
• Phanerozoic (570 Million years to the Present)
• The eon of complex life

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

7. FOUR Eras…
• PRE-CAMBRIAN – 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

8. 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?

11. Paleozoic Era (Ancient Life)
• 542MYA ------- 250MYA
• The Paleozoic Era is broken up into six periods.
• The Cambrian period is the 1st period of the Paleozoic Era. “Age of the
Trilobites”.
• Ordovician Period: The only life on Earth was found in the seas.
However, by the end of the Ordovician Period, life moved to land.
Plants began to colonize out of the water paving the way in later
periods for animals to follow.
• The Silurian Period saw various invertebrates move on to land.
• The following period, the Devonian Period, saw vertebrates join the
other types of animals on land. The first ones to leave the water were
similar to amphibians and they eventually evolved into reptiles

12. Paleozoic Era
• The Carboniferous Period, is sometimes broken into
two separate periods called the Mississippian Period
and the Pennsylvanian Period.
• It is named the Carboniferous Period because much
of the coal we use today was made during the later
stages of this time period.
• The final period of the Paleozoic Era is the Permian
Period, the largest mass extinction ever on Earth
happened. This mass extinction, known as the
Permian Extinction, completely wiped out about 95%
of all life in the oceans on Earth.

13. Trilobites
• Lived in Earth’s ancient seas
• Extinct before the dinosaurs came
into existence
• Cambrian Period is know as the
“Age of the Trilobites” (put in on
table)

14. Brachiopods
• Marine animals that resemble clams.

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

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

17. Early Land Plants
Cone bearing plants
Ferns
Mosses

18. Mesozoic Era – Middle Life
• The Mesozoic Era is sometimes called "age of the dinosaurs“
• Began 250MYA.
• The Triassic Period: First small dinosaurs appeared in this
period.
• On land, the amphibians and small reptiles like turtles were
dominant during the early Triassic Period.
• The Jurassic Period: Larger and more abundant dinosaurs
appeared in this period.
• Land animals during the Jurassic Period had more diversity
• At the end of the Jurassic Period, birds evolved from
dinosaurs.

19. Mesozoic Era
• The Cretaceous Period:
• Flowering plants appeared during the END of
this era.
• On land, the first small mammals started to
appear during the Cretaceous Period
– The mammals were small, warm-blooded animals.
Hair covering their bodies.

20. Mesozoic Era
• The main plant life of this time were Gymnosperms
or plants that produce seeds, but no flowers.
• 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.
• Many scientists believe that this event was caused by
a comet or asteroid colliding with the Earth.

21. Dinosaurs Mesozoic Reptiles
Mesozoic Mammals Mesozoic Plants

22. 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.
• Tertiary period:
– Paleogene
– Neogene
• Quaternary Period
• 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 animals

23. Cenozoic Era
• Growth of 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”

24. Cenozoic Era
• Marine animal examples:
– Algae, Mollusks, 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.

25. Cenozoic Mammals
Flowering Plants were common during the Cenozoic Era

26. Phanerozoic