The document discusses the geologic time scale, which is the standard timeline used to describe Earth's history and the events that formed rocks and fossils. The geologic time scale is broken into a hierarchical structure of eons, eras, periods, and epochs. The Precambrian eon spans from 4.6 billion to 541 million years ago and contains little fossil evidence. The Phanerozoic eon is divided into the Paleozoic, Mesozoic, and Cenozoic eras based on major changes in ancient fauna, with each era dominated by a particular animal group.

1. Describing the
History of Earth
Through
Geologic Time
EARTH
SCIENCE
11
STEM
Nobility
Week 8 Quarter 4

2. GEOLOGIC TIME
SCALE
In portraying the Earth’s
history, the most important
tool used is the Geologic Time
Scale. The age of rocks and
fossils, including the events
that formed them are
described in the said standard
timeline.

3. GEOLOGIC TIME
SCALE
It is broken into a hierarchical
set of divisions. The generally
accepted divisions are: “eons”
which are the largest blocks
of time on the geologic time
scale which are split into
“eras”.

4. GEOLOGIC TIME
SCALE
Eras are divided into
“periods”, and periods are
further divided into “epochs”.
There are two highest levels
of the hierarchy shown at
the left side of the scale, the
Precambrian and
Phanerozoic.

5. GEOLOGIC TIME
SCALE
Precambrian is
divided into three
eras: Hadean,
Archean, and
Proterozoic.

6. GEOLOGIC TIME
SCALE
Only very little is known
about the Precambrian which
extended from about 4.6
billion years ago to 541
million years ago because
there are only very few fossils
or unaltered rocks that have
survived from this time.

7. Phanerozoic eon
Based on further studies
conducted, geologists found out
that animals with evolving
external skeletons like shells
appeared during this time. Then
animals that formed internal
skeleton such as bony elements
of vertebrates appeared next.

8. Phanerozoic eon
There are three major
divisions of the
Phanerozoic eon - the
Cenozoic, the Mesozoic,
and the Paleozoic Eras.

9. Phanerozoic eon
The suffix "zoic" comes
from the root "zoo", which
means animal. "Cen"
means recent, "Meso"
means middle, and
"Paleo" means ancient.

10. Phanerozoic eon
Major changes in the
composition of ancient
faunas are reflected in the
said divisions. Every era is
being identified through a
particular group of animals
that dominated during such
time.

11. Phanerozoic eon
The Cenozoic era is also
known as the "Age of
Mammals". This is the last
and current division
extending from the extinction
of dinosaurs, nearly 66
million years ago to the
present.

12. Phanerozoic eon
Mesozoic era, the "Age of
Dinosaurs" or “Age of
Reptiles” extended
from 252 to 66 million years
ago. Both marine and
terrestrial ecosystems were
dominated by dinosaurs and
other reptiles.

13. Phanerozoic eon
It is worth noting also that it
was during the Mesozoic era
when the last of Earth’s
supercontinent known as
Pangaea was formed and
later broke up resulting into
the Earth’s current geography

14. Phanerozoic eon
Paleozoic era, known as the
"Age of Fishes" extends from
541 to 252 million years ago.
Life evolved in the oceans
and gradually colonized the
land, as revealed by fossil
evidence.

15. Phanerozoic eon
Although there were other groups of
animals that lived during the
Mesozoic era, and in addition to the
dinosaurs, animals such as mammals,
turtles, crocodiles, frogs, and
countless varieties of insects also lived
on land, always remember that every
division is identified by the
dominating group of animals.