Geological History of the Earth
Learning Objectives
At the end of the lesson, I should be able to;
• describe how earth’s history can be
interpreted from geologic time scale,
• characterize each major and subdivisions
in the geologic time scale, and
• describe how relative and absolute dating
provide evidence of geologic history.
We call this as GEOLOGIC TIME
SCALE. This is built from a long
process of study and investigation.
GEOLOGIC TIME SCALE
- is a record of the earth's geologic
history as scientists have come to
understand it by studying the layers in
rock. The geologic time scale is broken
up into larger and smaller subdivisions,
which help us get a better sense of
how historical events fit together.
Humans compose only a small
fraction of geologic time, only the
last 2 million years (2,000,000
years). In contrast, the Earth is
much, much older. In fact, it is more
than 2000 times older than all of
human history. The entire history of
the Earth is estimated (by
radiometric dating) to be about 4.6
billion years old. (4,600,000,000
years).
Paleontologist is a scientist who
studies the history of life on Earth
through the fossil record.
Fossils serve as markers that give us
clues for building everything we
know about prehistory.
Fossils can be of the following:
Index fossils
True form fossils Fossils preserved
Remains of plants and Trace fossils
(whole organism) in amber
animals that have existed
only for a limited geologic
period.
I. Precambrian Eon
- Beginning of the Earth (4.56
billion years ago)
- It can be divided into 3 specific
Eons which are the Hadean, the
Archean and the Proterozoic.
A. Hadean Eon
- From the Greek word “Hades”,
meaning “Hell”
- Earth is party molten surface
- Planetary Bombardment
- Volcanism
- Toxic gases (methane, ammonia,..)
- No fossils found
I. Precambrian Eon
B. Archean Eon (2.7 b.y.a)
- Earth began cooling down
- Rocks are formed from
magma
- Water condensed then
oceans remained
- Earths atmosphere was
mostly methane and
nitrogen.
- First life: Cyanobacteria Stromatolites are the
( convert CO2 to O2) Cyanobacteria from stromatolites oldest known fossil record
of life on Earth.
use photosynthesis to produce the
first oxygen in air
*b.y.a. – billion years ago
I. Precambrian Eon
C. Proterozoic Eon (2.5 billion to 541
million years ago)
- Algae and bacteria populate
- Most of the continental mass was
united as the supercontinent Rodinia.
- The “Snowball Earth” happened due to
reduction of volcanic activities
- Presence of ozone
- Life begin at the sea (sponges,
jellyfishes etc.)
Everything was going steadily,
with Algae and early plants
supplying oxygen, and bacteria
evolving….
…. BUT there were only few
species and life has still not
dominated on Earth.
…End of Precambrian Eon The Cambrian explosion, Cambrian radiation,
Cambrian diversification, or the Biological Big
Bang was a period of evolutionary history when
large numbers of new life forms emerged.
II. Phanerozoic Eon
- started about 541 million
years ago up to the present
- This eon can be divided into
three Eras: Paleozoic, Mesozoic,
and Cenozoic
A. The Paleozoic Era
- “Ancient life”
- The Paleozoic Era can be
subdivided into six geologic periods.
These include: the Cambrian,
Ordovician, Silurian, Devonian,
Carboniferous, and Permian Periods.
A. The Paleozoic Era
a. Cambrian Period
- Climate was milder
- Diversification of
marine life
- Invertebrates
- First fishes
(jawless)
- ALL LIFE was
under the sea
A. The Paleozoic Era
a. Cambrian Period
-What first
appeared: Trilobites, ANOMALOCARIS SPONGES
fish, arachnids etc.
ancestral form of
arthropod (spiders,
cockroaches, insects,
shrimps etc.)
PIKAIA (ancestors of fish and
OPABINIA vertebrates)
Trilobites
• Lived in Earth’s ancient seas
• Extinct before the dinosaurs
came into existence
• Cambrian Period is know as
the “Age of the Trilobites”
A. The Paleozoic Era
b. Ordovician Period
- Diversification of
marine life
- First primitive
plants began to
appear on land
- First animal with
bones appear
(conodonts)
A. The Paleozoic Era
b. Ordovician Period
Eurypterids, or “sea scorpions,” are an
extinct group of chelicerates, arthropods
related to horseshoe crabs, scorpions,
spiders, mites, and ticks.
Conodonts – descendants of animals that
gave rise to the vertebrates and jawed fish
Lichen helps create
A. The Paleozoic Era the first real soil
c. Silurian Period
Andreolepis, a jawed
fish of the Silurian
- True jawed fish period
- First land plants
appear and land
animals follow
- First freshwater fish
- Insects (millipeds,
centipedes, and other
arachnids)
- First terrestrial food Eurypterid “sea scorpion”
web Cooksonia (one of the most devastating
– first vascular plants predators)
A. The Paleozoic Era
d. Devonian Period
Age of Fishes
- First fish evolved legs
- First amphibians
- Gave the insects
advantage to
conquer the early
land.
- First seed-bearing
plants
Eryops (ancestors of frogs, toads,
and salamanders)
Lyginopteris
Arthropleura (ancestors of
millipedes and centipedes)
A. The Paleozoic Era
e. Carboniferous Period
- Highest oxygen content
- First reptiles evolved
from amphibians
- Rich deposits of coal over
time
(Protodonata) Large
dragonflies as wide as
Laptops
Reptiliomorphs
(first reptiles that lay
eggs on land)
Hylonomus (ancestor of lizard)
A. The Paleozoic Era
f. Permian Period
- Formation of Pangea
- Dry climate favored
reptiles
- First gymnosperms (cone
plants)
- Dominated with reptiles
Gymnosperm
(cone plants) Ivantosaurus (giant therapsids)
Pelycosaurs
(not dinosaurs, ancestors of
dinosaurs)
Therapsids with fur
(ancestors of mammals)
Reptiles were expanding this
period, but a sudden and
worldwide extinction happened,
ending this period. 90% of the
species become extinct.
It was suspected that global warming
and volcanic activity were the main
causes of this extinction.
PERMIAN EXTINCTION: THE GREAT DYING
II. Phanerozoic Era
- started about 541 million years ago up to the present
- This eon can be divided into three Eras: Paleozoic, Mesozoic,
and Cenozoic
A. The Mesozoic Era
- from 252 Mya end ended about 66
Mya
- the age of reptiles (giant reptiles,
dinosaurs and other monstrous beasts
roamed the Earth)
- This era can be subdivided into
3 periods – these include the Triassic,
the Jurassic and the Cretaceous
Periods.
A. The Mesozoic Era
A. The Triassic Period
- After the slow recovery Pelycosaur
from Permian extinction,
many kinds of reptiles
evolved (mostly diapsid
Pterosaur
reptiles). Late in the
period, the first mammals
appeared.
Ichthyosaur
A. The Mesozoic Era
A. The Triassic Period
- Unlike reptiles, most
mammals do not lay eggs.
Mammals are warm-
blooded animals that
nourish their young milk.
Triassic mammals, such as
Megazostrodon were small
rodent-like animals.
Triassic-Jurassic Extinction Event
- Huge and widespread volcanic eruptions triggered the end-
Triassic extinction. Some 200 million years ago, an increase in
atmospheric CO2 caused acidification of the oceans and global
warming that killed off 76 percent of marine and terrestrial
species on Earth.
A. The Mesozoic Era
Sauropods
B. The Jurassic Period
- Dinosaurs developed Allosaurus Stegosaurus
into a varied and (carnivores) (herbivores)
widespread group
Archeopteryx
- The early ancestors (flying reptile)
of birds were probably
small, feathered
dinosaurs that could Velociraptor
glide.
A. The Mesozoic Era Plesiosaurs
B. The Jurassic Period
- In the oceans, fish with
modern characteristics
evolved.
- Reptiles adapted to life in
the oceans. Fish eating
plesiosaurs and
ichthyosaurs became good
swimmers but kept
reptilian teeth and
breathed by means of lungs.
Ichthyosaurs
Tyrannosaurus Rex
A. The Mesozoic Era
C. The Cretaceous Period Triceraptors
- landscape had a lot of
flowering plants ( pollinators)
- New breeds of dinosaur
came to grow up.
- Placental mammals Troodons
Ankylosaurus
A. The Cretaceous Period
A. The Cretaceous Period
C. The Cenozoic Era
C. The Cenozoic Era: Tertiary Period
Plesiadapiforms
(Primate-like species)
Titanoboa (ancestors of
snake) Oxyaena (wolverine-like
carnivore)
C. The Cenozoic Era: Quaternary Period
The End
