Life Science
Unit 8 Lesson 6
Geologic
Time and
Development
of Life
Attendance link: http://goo.gl/forms/vLJBqFc8XB

The Painted Desert, Arizona. This landscape
has a story to tell, and each individual rock and
even the colors mean something about the
past.
EXPECTATIONS
Required Class Connects
Tuesday, Wednesday, & Thursday
1:30-2:30 pm
Be active and participate in class.
Be respectful to your classmates
Be positive in the chat box and use it correctly.
Have a working microphone!
You will need it during the lessons and break out rooms.
If you have a question, please place it in the chat box
3
and repost it if I don’t see it.
3
Objectives
Describe the development of life on earth.
 Identify the age of the earth, on the basis
of current scientific theory.

Precambrian Era
This is the longest era of earth’s history
and the oldest.
 The environment was different then it is
today.

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
The atmosphere contained no oxygen.
It was composed mostly of water vapor,
carbon dioxide, and nitrogen.
The first organisms were single-celled
prokaryotes
Time moves on
Evidence suggests that prokaryotes
dominated earth’s surface for about 2
billion years.
 Cyanobacteria kept pumping oxygen into
the air, creating both an oxygen-rich
atmosphere and a protective layer of
ozone.
 Earth’s surface slowly became a less harsh
environment. In part because of these
changes, the first eukaryotic cells
appeared about 1.5 billion years ago,
according to the fossil record.

Enter the
Paleozoic Era
Life starts in the seas and moves onto land
570,000,000 years ago to 225,000,000 years ago
Six periods:
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
Bring on the Trilobites

It was during the Paleozoic Era that
trilobites lived.
Paleozoic
• Animals diversified into all phyla present today.
• Sharks first swam in the water.
• The first plants appeared on land.
• The first insects appeared.
• At the end trilobites become extinct.
Mass Extinction
Each geologic era is defined by a major
change in earth’s surface or in the types
of organisms that existed on earth.
 The largest mass extinction of earth’s
history marked the end of the Paleozoic
era. Roughly 250 million years ago, nearly
90 percent of earth’s marine organisms,
such as trilobites, became extinct. Entire
groups of organisms were wiped out.

Mass Extinction
One of the Big FIVE Mass Extinctions
This extinction began the next era:
the Mesozoic era.
This is the Age of Reptiles.
 This era is divided into three periods:

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Triassic
Jurassic
Cretaceous
Mesozoic
Dinosaurs become extinct.
 The first mammals appeared.
 The first flowering plants appeared.

Another mass extinction bring on
the Cenozoic Era.
This is the Age of Mammals.
 During the Cenozoic, mammals evolved
from a few small, rat-like species into an
incredibly varied collection of land,
aquatic, and even flying animals.
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These include woolly mammoths, sabertoothed cats, giant ground sloths, bats, cows,
and even humans.
The Cenozoic era also saw an increase in
the variety of insects and an explosion in
the number of flowering plants.

Life on earth is very different today than
when it first appeared. The first organisms
were microscopic prokaryotic organisms
similar to modern archaea and bacteria.
After 3.5 billion years, earth as we now
know it is teeming with diverse life.

The fossil record of the hard parts is beautifully
preserved, along with a carbon film, showing a
detailed outline of the fish and some of its
internal structure.

These logs of petrified wood are in the Petrified
Forest National Park, Arizona.
The Grand Canyon, Arizona, provides a majestic
cross section of horizontal sedimentary rocks.
According to the principle of superposition,
traveling deeper and deeper into the Grand
Canyon means that you are moving into older
and older rocks.
This dinosaur footprint is in shale near Tuba
City, Arizona. It tells you something about the
relative age of the shale, since it must have
been soft mud when the dinosaur stepped here.

Geological Clocks and finding the age of the
earth.
 Process
must have been present since the
Earth was first created
 The process must occur at a uniform rate
 The process must be able to be measured
 Clocks
 Rate
considered
of salt addition to the ocean
 Resulted in an age for the Earth of 100
million years
 Rate of sediment deposition
 Resulted in an age for the Earth of 20 to
1,500 million Years
 Rate of cooling of the Earth
 Resulted in an age for the Earth of 20 to
40 million

Modern Techniques

Radioactive decay
 Measure
the rate of radioactive decay of
unstable elements within the crystals of
certain elements.
 Since decay rates are constant the ratio of
the decay product to the remaining
amount of the original element can be
used as a measure of the age of the
material in which it is found.
Geologic history is divided into four main eras.
The Precambrian era was first, lasting the first 4
billion years, or about 85 percent of the total
4.6 billion years of geologic time. The Paleozoic
lasted about 10 percent of geologic time, the
Mesozoic about 4 percent, and the Cenozoic
only about 1.5 percent of all geologic time.
Ripple Marks, Bay Beach
Fossil Ripple Marks, Baraboo Range
Modern Mud Cracks
Fossil Mud Cracks, Virginia
Dinosaur
Tracks,
Texas
Assignment

OLS

Online – 5 questions
Make sure you are mastering ALL of your
lessons!
 We are in the last push of the year. Stay
on top of your work so that you can finish
on time!

Cambrian Period
(570-500 MYA)

Cambrian Explosion – Most major animal phyla are found in
the fossil record (mostly aquatic invertebrates with
exoskeletons).

Burgess Shale – major fossil site located in Canadian Rockies
Ordovician Period
(500-435 MYA)
1st vertebrates - jawless fish (filter feeders)
 The vertebrate protects the spinal cord,
which carries signals from the brain
throughout the body.
The lamprey of today is a parasite.
The hagfish is a scavenger.
Silurian Period
(435-395 MYA)

1st jawed fish (later evolved into sharks-made of
cartilage).

Ozone (O3) layer formed which blocks harmful UV
radiation; life could evolve on land.

1st land plants (mosses & ferns) followed by 1st land
animals (arthropods-spiders & scorpions).
Devonian Period
(395-345 MYA)

“Age of the Fish” (giant armored fish).
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1st bony fish (scales and swim bladder for buoyancy).
Devonian Period
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(395-345 MYA)
1st vertebrates on land – amphibians
 Evolved from the lobed-fin fish which include some
species of lungfish.
Carboniferous Period
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North America is at the equator (tropical swamps form coal deposits)
Amphibians & insects dominate and become large

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(345-280 MYA)
(dragon flies-1m wing span; cockroaches-10 cm long).
1st reptiles
Permian Period
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(280-225 MYA)
Reptiles dominate.
Pangaea begins to form (Appalachian Mnts; dry climate; ice age in
the southern hemisphere)
Mass Extinction (90% of all species go extinct-mostly marine
invertebrates).
Early Permian reptiles, Cacops in front
& Casea in back.
The middle Permian reptile, Anteosaurus.