The document outlines the geologic time scale, divided into eons, eras, periods, and epochs, detailing significant events in Earth's history. It highlights developments from the formation of the Earth through various biological milestones, including the emergence of significant life forms during the Paleozoic, Mesozoic, and Cenozoic eras. Key periods such as the Cambrian, Jurassic, and Cretaceous are noted for major evolutionary changes and mass extinction events.

1. GEOLOGIC TIME SCALE

2. • EONS
–an immeasurably or indefinitely long period of
time. Lasts for hundreds of millions of years.
• ERA
– a period of time known for particular events
or developments. One Era is hundreds of
millions of years in duration.
UNITS OF TIME

3. • PERIOD
–This is the basic unit of geologic time. A Period
lasts tens of millions of years, which is the
time it takes to form one type of rock system.
• EPOCH
– unit of geological time during which a rock
series is deposited.
UNITS OF TIME

4. EONS
• Hadean
• Archean
• Proterozoic
• Phanerozoic

5. ERA
• Precambrian
• Paleozoic
• Mesozoic
• Cenozoic

6. PERIOD
• Precambrian
– Beginning of earth
• Paleozoic
– Cambrian
The Cambrian Period marks an important
point in the history of life on Earth; it is the
time when many kinds of invertebrates
and the first vertebrates—fishes—
appeared in the fossil record.

7. PERIOD
• Paleozoic
– Ordovician
During the Ordovician period, part of
the Paleozoic era, a rich variety of
marine life flourished in the vast
seas and the first primitive plants
began to appear on land.

8. PERIOD
• Paleozoic
– Ordovician
Possibly the most remarkable biological
event during the Silurian was the evolution
and diversification of fish. Not only does this
time period mark the wide and rapid spread
of jawless fish, but also the appearances of
both the first known freshwater fish and the
first fish with jaws.

9. PERIOD
• Paleozoic
– Devonian
The Devonian, part of the Paleozoic era, is
otherwise known as the Age of Fishes, as it
spawned a remarkable variety of fish. The
most formidable of them were the armored
placoderms, a group that first appeared
during the Silurian with powerful jaws lined
with bladelike plates that acted as teeth.

10. PERIOD
• Paleozoic
– Mississippian
During the Mississippian sea lilies
dominated the seas and reptiles began to
appear on land, along with ferns. Shallow,
warm seas supported dense meadows of
crinoids and blastoids along with corals,
arthropods and mollusks.

11. PERIOD
• Paleozoic
– Pennsylvanian
The Pennsylvanian was a time of major
climate change, with oscillations between
glacial and interglacial phases and overall
increased warming and drying over the
duration of the subperiod. When rainfall was
high during glacial periods, swamp forests
thrived in the equatorial regions.

12. PERIOD
• Paleozoic
– Permian
Earth's crustal plates formed a single, massive
continent called Pangaea. In the correspondingly
large ocean, Panthalassa, marine organisms such
as brachiopods, gastropods, cephalopods
(nautiloids and ammonoids), and crinoids were
present. On land, reptiles replaced amphibians
in abundance.

13. PERIOD
• Mesozoic
– Triassic
The start of the Triassic period was a desolate time in
Earth's history. Something—a bout of violent volcanic
eruptions, climate change, or perhaps a fatal run-in with a
comet or asteroid—had triggered the extinction of more
than 90 percent of Earth's species. But it was also a time
of tremendous change and rejuvenation. Life that
survived repopulated the planet, diversified into freshly
exposed ecological niches, and gave rise to new
creatures, including rodent-size mammals and the first
dinosaurs.

14. PERIOD
• Mesozoic
– Jurassic
The Jurassic period (199.6 million to 145.5
million years ago) was characterized by a
warm, wet climate that gave rise to lush
vegetation and abundant life. Many new
dinosaurs emerged—in great numbers.
Among them were stegosaurs, brachiosaurs,
allosaurs, and many others.

15. PERIOD
• Mesozoic
– Cretaceous
The Cretaceous Period ends with one of the greatest
known extinction events, so severe it also marks the end
of the Mesozoic Era. During this period, oceans formed
as land shifted and broke out of one big supercontinent
into smaller ones. The Cretaceous is usually noted for
being the last portion of the "Age of Dinosaurs", but that
does not mean that new kinds of dinosaurs did not
appear then. Tyrannosaurus rex arose during the
Cretaceous period about 85 million years ago, and
thrived as a top land predator.

16. PERIOD
• Cenozoic
– Tertiary
The Tertiary Period began abruptly when a
meteorite slammed into the earth, leading to
a mass extinction that wiped out about 75
percent of all species on Earth, ending the
reptile-dominant Cretaceous Period and
Mesozoic Era.

17. PERIOD
• Cenozoic
– Quaternary
The Quaternary Period has involved dramatic
climate changes, which affected food
resources and brought about the extinction of
many species. The period also saw the rise of
a new predator: man.