Birth of a Planet

The history of Universe began
about 13.7 billion years ago with
the Big Bang.

The Big Bang is a theory on how
the universe formed.

Theory – an explanation of some
aspect of the natural world, based
on a body of facts that have been
repeatedly confirmed through
observation and experiment.

Theories cannot be DIRECTLY
TESTED; therefore theories can
never be considered a fact.

This provided the elements to
form the solar system
○ As material collected, high-
velocity impacts of matter, called
planetesimals, caused Earth’s
temperature to increase
Birth of a Planet

Formation of Earth
 Earth formed roughly
4.6 Billion Years Ago
(BYA)
○ Iron and nickel
melted and sank
to form the
metallic core
while rocky
material rose to
form the mantle
and Earth’s crust
Development of the Atmosphere and
Oceans
During Precambian Time (4.6 Billion Years Ago
– 544 Million Years Ago), the Earth’s two
atmospheres formed.
 Earth’s First Atmosphere:

 The Earth and its atmosphere was very hot.
 The Earth was impacted by space debris such as
meteors, comets, and asteroids.
 The two gases that made up the first atmosphere
were: Hydrogen (H) and Helium (He).
 The Hydrogen and Helium eventually left the Earth’s
atmosphere because they were so hot.
 Hot gas molecules move very fast and drifted off into
space.
Development of the Atmosphere and
Oceans

Earth’s Second Atmosphere
 Earth’s 2nd Atmosphere came primarily from Earth
itself.
 There were lots of volcanoes, many more than today,
because Earth’s crust was still forming. The
volcanoes released
○ steam (H2O, with two hydrogen atoms and one oxygen
atom),
○ carbon dioxide (CO2, with one carbon atoms and two
oxygen atoms),
○ ammonia (NH3, with one nitrogen atom and three
hydrogen atoms).
 Comets also added water (H2O), Carbon Dioxide,
and Nitrogen (N).
○ Comet – a ball of dust and ice that orbits the sun.
Development of the Atmosphere
and Oceans

Water vapor condensed to form clouds
and rainwater that formed the oceans

About 3.5 billion years ago in the oceans,
photosynthesizing bacteria began to
release oxygen
○ Oxygen levels steadily increased over
time
○ Eventually oxygen levels were sufficient
for ozone to develop in the atmosphere
Development of the Atmosphere and
Oceans
Geologic Time Scale
Divides geologic history into units.
Originally created using relative dates.
We will discuss how we accurately date in
the next target
o Subdivisions
o
o
o
o Eon
o Greatest expanse of time
o Four eons (Greek terms)
o Phanerozoic (542 Million Years Ago – Present)
(“visible life”) – the most recent eon
o Proterozoic (“earlier life”) – such as bacteria
o Archean (“beginning”)
o Hadean – comes from the term Hades (Greek god
of the Underworld) because Earth was fiery like
the Underworld – the oldest eon.
Geologic Time Scale
o
Subdivisions
o Era
o Subdivision of an eon
○ Eras of the Phanerozoic eon
• Cenozoic (“recent life”)
• Mesozoic (“middle life”)
• Paleozoic (“ancient life”)
• Eras are subdivided into periods
• Periods are subdivided into epochs
• WE WILL FOCUS ON ERAS AND
PERIODS of the PHANEROZOIC EON!!!
The Geologic Time Scale
Precambrian History

The Precambrian, which is composed of
the Hadean, Archean, Proterozoic eons,
spans almost 90% of Earth’s history
○ Much of Earth’s stable continental crust
was created during this time
 Larger crustal areas were assembled into
larger blocks called cratons
 Cratons form the core of modern continents
Formation of
continental crust
Precambrian History

Supercontinents
○ Large landmasses that consist of all, or nearly
all, existing continents
○ Pangaea was the most recent, Rodinia,
preceded it
○ Splitting and reassembling of supercontinents
have generated most of Earth’s major mountain
belts
○ Supercontinents have also profoundly affected
Earth’s climate over time
Possible configuration
of Rodinia
Phanerozoic Eon History

Phanerozoic eon encompasses 542
million years
○ Divided into the Paleozoic, Mesozoic,
and Cenozoic eras

Paleozoic era
○ Dominated by continental collisions as
Pangaea began to assemble
 Formed the Caledonian, Appalachian, and Ural
Mountains
Formation of Pangaea
Phanerozoic History

Mesozoic era
○ Early in the Mesozoic, much of the land
was above sea level
○ By the middle Mesozoic, seas invaded
western North America
○ Pangaea began to break apart and the
westward-moving North American plate
began to override the Pacific plate
Phanerozoic History

Mesozoic era
○ Pangaea began to break apart and the
westward-moving North American plate
began to override the Pacific plate
 Resulted in crustal deformation along the
entire western margin of North America
 Formed the Sierra Nevada and Rocky
Mountains
Phanerozoic History

Cenozoic era
○ Much of North America was above sea
level throughout the Cenozoic
 Eastern and western margins of the continent
experienced markedly contrasting events
 Atlantic and Gulf coastal regions, removed
from active plate boundaries, were
tectonically stable
Phanerozoic History

Cenozoic era
○ Much of North America was above sea
level throughout the Cenozoic
 In the West, the Rocky Mountains was ending,
the Basin and Range Province was forming,
and volcanic activity was extensive
Earth’s First Life

First known organisms were singlecelled bacteria, prokaryotes, which
lacked a nucleus
○ One group of prokaryotes, called
cyanobacteria, used solar energy to
synthesize organic compounds, thus
producing their own food
 Fossil evidence of these bacteria include
layered mounds called stromatolites
Paleozoic Era: Life Explodes

The Paleozoic Era is divided into the
following periods:





Cambrian (544 – 505 million years ago)
Ordovician (505 – 438 million years ago)
Silurian (438 – 360 million years ago)
Devonian (408 – 360 million years ago)
Carboniferous (360 - 320 million years ago)
○ Composed of two epochs: Mississippian and
Pennsylvanian epochs)
 Permian (286 – 245 million years ago)
Paleozoic Era: Life Explodes

Paleozoic marks the first appearance of lifeforms with hard parts such as shells
○ Resulted in abundant Paleozoic fossils.

Cambrian Period - Life in the early
Paleozoic was restricted to the seas and
consisted of several INVERTEBRATE
groups including




Trilobites
Cephalopods
Sponges
Corals
○ Invertebrates – animals without backbones.
Paleozoic Marine Invertebrates
Paleozoic Era: Life Explodes

During the Paleozoic, organisms diversified
dramatically.

Silurian Period
 Insects and plants first appeared on land.

Devonian Period – Age of Fishes
 Fishes, such as sharks and fish with scales, dominate the seas
 Lobe-finned fish adapted to land and became the first amphibians.
 First land animals appear during the Devonian Period

Carboniferous Period
 Large tropical swamps in the Pennsylvanian epoch became the
major coal deposits of today.
 The first true reptiles appeared.
Pennsylvanian-age coal swamp
Paleozoic Era: Life Explodes

During the Paleozoic, organisms diversified
dramatically
○ A mass extinction at the close of the Paleozoic
destroyed 70% of all vertebrate species on
land and 90% of all marine organisms

Scientists are not sure why the extinction
occurred but is evident from fossil layers.
Mesozoic Era: Age of the Reptiles

The Mesozoic Era is divided into the
following periods:
 Triassic (245 – 208 million years ago)
 Jurassic (208 – 144 million years ago)
 Cretaceous (144 – 66 million years ago)
Mesozoic Era: Age of the Reptiles

Mesozoic, literally the era of middle life, is often
called the “Age of Reptiles”
Organisms that survived the extinction at the end
of the Paleozoic began to diversify
 Fish, reptiles, and cone-bearing trees called
conifers survived (ex. Pine trees)

 Reptiles became the dominant land animals
 First reptiles were small, but evolved rapidly, particularly the
dinosaurs
Mesozoic Era: Age of the Reptiles

Triassic Period
 First dinosaurs appeared about 225 million years ago.
 First mammals appeared
○ Mammals- warm-blooded vertebrate that feeds its young milk
○ The mammals were mouse-sized
 Conifers (cone-bearing trees (ex. Pine trees)), palm-like trees, and
ginkgo trees made up forests

Jurassic Period
 First birds such as Archaeopteryx and Pterodactyl appear
 Dinosaurs became dominate although most were herbivores and
the largest dinosaurs, such as Stegosaurus, existed

Cretaceous Period – Age of the T. Rex
 The T.Rex and other carnivorous dino theropods (some larger)
dominated the land.
 The first flowering plants appears with fruits.
Theropod Sizes
Archaeopteryx fossil
Figure 12.32
Mesozoic Era: Age of the Reptiles

At the close of the Mesozoic, another mass
extinction occurred.
○ Many reptile groups became extinct
○ A few types survived, including the turtles,
snakes, and lizards.

Most scientists believe an asteroid hit the Earth near
the present-day Yucatan Peninsula in Mexico.

Other scientists believe climate change caused by a
volcanic eruption or a parasite caused the mass
extinction.
Cenozoic Era: Age of Mammals

The Cenozoic Era is divided into the
following periods:
 Tertiary (66 – 1.8 million years ago)
 Quaternary (1.8 million years ago – present
time)
Cenozoic Era: Age of Mammals

In the Cenozoic, mammals replaced the
reptiles as the dominant vertebrate lifeforms on land
○ One tendency was for some mammal groups
to become very large

Tertiary Period
 Whales and dolphins first evolved
 The first grazing animals thrived as grasses began
to cover the continents.
Cenozoic Era: Age of Mammals

Quaternary Period
 A series of Ice Ages occurred as the Earth’s climate
cooled.
 Many giant mammals, such as the woolly mammoth and
sabored-tooth tiger died off after an ice age ended 10,000
years ago.
 Today’s atmosphere is about 78% nitrogen, 21% oxygen,
and 1% carbon dioxide and other gases.

The Cenozoic could also be called the “Age of
Flowering Plants”
○ Flowering plants (angiosperms) strongly influenced
the evolution of both birds and herbivorous
mammals throughout the Cenozoic