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Geologic Time Scale

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Dean Chigounis

on 18 September 2015

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Transcript of Geologic Time Scale

Geologic Time Scale
Life Explodes after 40 minute mark
Geologic Time Scale
scale used by geologists, paleontologists, and earth scientists that divides the history of Earth into time intervals based on geological record.

Two time scales are used to measure the age of earth:

Relative time scale
– based upon the sequence of layering (strata) of rocks and the evolution of life.

Radiometric time scale
– based upon natural radioactivity of chemical elements in rock. (carbon-14 dating video)

Geologic Time Scale
Key Principles of geological time scale:

1. Rock layers (strata) are laid down in succession with each strata representing a slice of time.

2. The principle of superposition – any given stratum is probably older than those above it and younger than those below it.


1. Sequence are often eroded, distorted, tilted, or even inverted and deposition.

2. Strata laid down at same time in different areas can have entirely different appearances.

3. Strata of any given area represents only part of history.

Geologic Time Scale
by D. Chigounis 2013
Geologic Timescale - Another Perspective
12:00am – Earth forms

7:00am - Earliest one-celled organisms appear

7:00am-9:00 pm- Simple, soft-bodied organisms like worms

Little past 9:00pm - Complex organisms evolve in oceans

Little past 10:00pm - Reptiles and insects first appear

Just before 11:00pm - Dinosaurs arrive

11:30pm - Dinosaurs go extinct

11:59pm - Humans appear one second before midnight

EON – largest division of geologic time

ERA – 2nd largest, includes two or more periods

PERIOD – 3rd largest, unit into which eras are divided

EPOCH – 4th largest, the subdivision of a period


Divisions of Time
Why is a time scale used to represent Earth’s history instead of a calendar?
Earth’s history is so extensive

When did Geologic time begin?
4.6 billion years ago (BYA)

When does Geologic time end?
It does not. We are now in the Quaternary Period of the Cenozoic Era (Phanerozoic Eon)

How long is a geologic period?
A period doesn’t have an exact length.

What Does It All Mean?
Eons (from past to present)
– rocks from meteorites and moon

– earliest rocks on earth form

– organisms with well developed cells

– means “visible life” well represented in the fossil record

– “early life” 544 to 244 mya

– “middle life” 245 to 66 mya

– “recent life” 66 mya to present

Which one do you live in today?

– Explosion of life
– 1st Vertebrates
– 1st Land Plants
– Age of Fish
– Winged insects
– First Reptiles
– Age of Amphibians
– First Dinosaurs/Small mammals
– First Birds
– Heyday of Dinosaurs
– Mammals Thrive
– Age of Man/Technology
Earth Formation
Earth formed 4.6 billion years ago.

Scientists think that Earth began as a ball of dust, rock and ice called a “nebula”

Gravity pulled this mass together.

As Earth grew larger, gravity increased. Pulled in nearby dust, ice and rock.

As objects hit Earth at high speeds, their energy changed into thermal energy.

Energy from collisions caused Earth’s temp to rise until planet was very hot.

Scientist believe Earth may have become so hot it melted.

Denser materials sank toward the center—formed Earth’s dense iron core.

At same time, Earth continuously lost heat to cold of space.

Less dense molten material hardened to form Earth’s outer layers. Oceans form.

Life Develops
We have fossils of single-celled organisms in rocks that formed 3.5 billion years ago... Probably in early ocean

Primordial Ooze – water contained the building blocks of life

Similar to present day bacteria.

About 2.5 billion years ago, simple organisms began using energy from sun to make their own food.

Photosynthesis slowly released oxygen into air, which created an "oxygen crisis", wiping out millions of organisms unable to cope with oxidation.

The Great Oxygen Revolution
Stromatolites - Proof of Life's Origin
Mass extinctions
There are FIVE major extinctions:

Largest: "Permian Extinction" aka "The Great Dying"
Largest extinction in Earth's history (96% of all species go extinct - remaining 4% of surviving life give rise to all life on Earth today).
Trilobites suddenly go extinct; climate change resulting from continental drift may have had role; formation of Pangaea caused deserts to replace tropics; ice sheets formed closer to South Pole; Volcanism releases massive amts. of carbon dioxide causing warming event.

Others of Note:
Ordovician - Silurian, Late Devonian, Triassic - Jurassic, Cretaceous - Tertiary (K/T)

Two Theories:

Asteroid hits earth, creating dust and water in atmosphere which blocks sunlight causing nuclear winter.
Volcanism increases atmospheric dust, blocking sun and cooling Earth.
Mass Extinctions
Earth's Mass Extinction
Cambrian Period

Cambrian Explosion
”- many new life forms appeared within a short time.

1st time organisms had hard parts-shells and outer skeletons.

All animals lived in the sea.

Many were invertebrates-jellyfish, sponges, worms that drifted through the water.

Brachipods (clams) and trilobites were common in the Cambrian seas.

Ordovician Period
Seas still cover the Earth
Ice cap covers what is now North Africa.
Ancestors of squid and octopus appear.
Jawless fish (agnatha) evolve—first vertebrates.

Silurian Period
Coral reefs develop
Prior to this period, only one-celled organisms lived on land.
Land plants appear
Fish with jaws (gnathastoma) appear.
Insects and spiders appear.

Devonian Period
Often called "Age of Fishes".

Every main group of fishes were present in the ocean.

Most fish had jaws, skeletons and scales on their bodies.

Sharks (chondrichthyes) appeared late in the period.

Animals begin to invade land.

1st vertebrates on land were lungfish. 1st amphibians evolved from the lungfish.

Carboniferous Period
Divided into Mississippian and Pennsylvanian.

Life expanded over continents. Appalachian Mountains began to form.

Small reptiles developed

Winged insects evolved-huge dragonflies and cockroaches.

Giant ferns & cone bearing plants and trees formed. “Coal forest”

Triassic Period
Fish, insects, reptiles, and cone bearing trees (conifers) survived Permian extinction.

1st dinosaurs appear

1st mammals appear-size of mouse

1st turtles and crocs appear

Gymnosperms (conifers), palm-like trees (cycads), ginko trees dominate forest

Pangaea holds together. Hot, dry conditions dominate center of Pangaea.

Jurassic Period
Dinosaurs become dominant land animal.

Some were plant eaters, some were meat eaters.

Different types lived at different times.

1st birds appear. Archaeopteryx means “ancient wing thing.”

1st flying reptiles-pterosaurs appear.

Pangaea breaks apart-N. America and S. America separate.

Cretaceous Period
Continents moved toward present location.

Widespread volcanic activity.

Flying reptiles and birds competed.

Birds hollow bones and feathers made them better adapted.

1st flowering plants “angiosperms”. Flowering plants produce seeds that are inside fruit. Fruit helps seed survive.

Dinosaurs dominate-Tyranosaurus-rex.

1st snakes appear.

The K/T Extinction occurs at the end of the Cretaceous, wiping out the dinosaurs!

Tertiary Period
Climate was warm and mild.

Rockies and Himalayas form.

Continental glacier covers Antarctica.

1st grasses appear-provide food source for grazing animals. (ancestors of cattle, deer, sheep.)

Flowering plants thrive.

Ancestors of humans evolve.

Quarternary Period
Climate cooled-causing a series of ice ages.

20,000 years ago climate began to warm.

Modern humans-Homo sapiens evolved as early as 100,000 years ago. 12,000-15,000 humans had migrated around the world.

Mammals, flowering plants (angiosperms), and insects dominate land.

Earth began 4.6 billion years ago in the form of a nebula or gas cloud.

Life began 3.5 bya.

Geological time is broken down into Eons, Eras, Periods, and Epochs based on fossil evidence and rock strata.

There were five great extinctions – theories suggest either by asteroid or volcanism – both, which altered earth’s climate.

We are currently living in the Quarternary Period of Cenozoic Era.

Geological Time Scale Summary
Formation of Earth
K/T Boundary
Law of SuperPosition
Quarternary Period
The History of Earth
To be viewed in class
Geologic Time Summary
Full transcript