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Earth HistoryMrs. Burkey

ESS Cy Creek HS

17-18

The Earth is 4.6 billion years

old!

If the Earth formed at midnight…

• 6:00 am – First life appears

• 10:00 pm – First animals/plants

on land

• 11:59 pm – First humans evolve

What is the Earth’s time scale?

The Geological time scale is a record of

the life forms and geological events in

Earth’s history.

Scientists developed the time scale by

fossils world wide.

Radioactive dating (like Carbon Dating)

helped determine the absolute divisions

in the time scale.

Geological time Scale

(largest to smallest)

Super-eon

Eon

Era* - 4

Period* -11

Epoch - Current

Age - Current

FOUR Eras…

PRE-CAMBRIAN – 88% of earth’s history

Paleozoic (ancient life) 544 million years ago…lasted 300 million yrs

Mesozoic (middle life) 245 million years ago…lasted 180 million yrs

Cenozoic (recent life) 65 million years ago…continues through

present day

Pre-Cambrian

Began with the formation

of the Earth 4.6 billion

years ago.

Accounts for 88% of whole

Earth History.

Simple bacteria only.

2

Paleozoic Era “Ancient Life”

Explosion of life in the oceans began

during this era.

Most of the continents were covered in

warm, shallow seas.

Invertebrates were dominate

Fish emerged which led to the arrival of

amphibians

The early coal forming forests were also

formed during this time. Carboniferous

Period

Paleozoic Era

Divided into 5 periods:

Cambrian period - “Age of the

Trilobites”

Ordovician period - First fishes

evolved and other species

become extinct

Silurian period - Land plants,

insects and spiders appear

Devonian period - Amphibians evolve and cone-bearing plants start to appear.

Carboniferous period - Tropical forests appear and reptiles evolve. Where we get most of our coal/fossil fuel now.

Permian period - Seed plants become common and insects and reptiles become widespread.

Mesozoic Era “middle life”

Dinosaurs were also very active in this era.

First small dinosaurs appeared in the Triassic Period.

Larger and more abundant dinosaurs appeared in the Jurassic Period.

Small mammals and birds also appeared during this era.

Mesozoic Era

Divided into 3 periods:

Triassic period - Turtles and crocodiles evolve and dinosaurs appear.

Jurassic period - Large dinosaurs roam the world. First mammals and birds appear.

Cretaceous period - Flowering plants appear, mammals become more common, dinosaurs become extinct.

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Mesozoic Mammals

Mesozoic Reptiles

End of the Mesozoic Era

This era ended with a mass extinction event

about 65 million years ago.

Many groups of animals, including the dinosaurs

disappeared suddenly at this time.

Many scientists believe that this event was

caused by a comet or asteroid colliding with

the Earth.

Cenozoic Era – “Recent Life”

Began about 65 million years ago and continues today!!!!!

Climate was warm and mild.

Marine animals evolved.

Mammals began to increase and evolve adaptations that allowed them to live in many different environments – land, air and the sea.

This era is sometimes called the “Age of Mammals”

Cenozoic Era

Divided into 2 periods:

Tertiary period - First

primates appear and

flowering plants

become the most

common.

Quaternary period -

Humans evolve and

large mammals like

woolly mammoths

become extinct.

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Mass Extinctions

Source:

http://dsc.discovery.com/earth/wide-angle/mass-

extinctions-timeline.html

#37-40, #6

Mass extinctions are NOT unusual

99% of all things that have ever lived, have gone extinct

There have been 5-6 major mass extinction events

Causes of Mass Extinctions

1. Asteroid or comet impacts

2. Climate changes

3. Volcanic eruptions

4. Sea level changes

5. Oxygen in the atmosphere

#37

Asteroid or Comet Impacts

Dust kicked up may block

out the Sun for years

Perennial winter

Global wildfires from

molten impact debris

Climate Changes

Shifts in climates can eliminate or

move entire habitats.

Plate Tectonics

Alters major circulation patterns

Volcanic eruptions

Living organisms can alter

atmospheric gas concentrations and

global thermostat

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Volcanic Eruptions

Some last hundreds or

thousands of years

Areas covered by vast deposits

of lava (flood basalts, traps)

Change global climate by

releasing large amounts of

carbon dioxide into atmosphere

Sea Level Changes

Affects mostly shallow coastal areas

Caused by climate change (melting/freezing of ice caps and glaciers) and tectonic activity

Oxygen in the Atmosphere

Highly variable, current level is 21%

Unicellular photosynthetic organisms

added oxygen for 2 billion years

(600 mya ~15%)

Explosion of multicellular life

2.5-2.2 bya(Precambrian era)

Almost all anaerobes

“Oxygen Holocaust”

Evolution of

photosynthetic organisms

added oxygen to the

atmosphere killing most

anaerobic organisms

445 mya(Late Ordovician period)

57% extinction

Most organisms lived in

the sea at this time

Causes

Sea level drop caused by

plate tectonics

Pangea over south pole

at this time – large

glacier

370 mya(Late Devonian period)

50% extinction

Causes

Fluctuating sea

levels

Land plants

removed CO2 from

atmosphere (global

cooling)

More glaciers

pulled water from

the oceans

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250 mya(End of Permian period)

83% extinction

The “Great Dying” event

96% of all marine species

70% of all land vertebrates

Arthropods

Land plants

Likely causes

Eruption of Siberian Traps

Formation of Pangaea – disrupted ocean currents

Possible meteor impact

#38, 40 200 mya(end of Triassic period)

48% extinction

Large marine extinction

Ammonites

Corals

Seed ferns

Likely caused by eruption of the

Central Atlantic province

Sulfur gas – blocked Sun

Large amount of lava released over

several centuries

K-T Boundary ~65 mya

50% extinction Asteroid impact

Break up of Pangaea

Eruption of Deccan Traps in India

Marks the end of the

Cretaceous period,

Mesozoic era

End of the “age of

reptiles” / dinosaurs

K

THow could volcanic eruptions

lead to sea level changes?

#39

Ash

blocks

out

sun

Gases

(SO2,

CO2)

add to

global

warmin

g

Temp

↓,

glacier

s form

Temp

↑,

glacier

s melt

SO2

gas

Ash Sea

level

drops

Sea

level

rises

Principle of Faunal Succession

• Fossils in rocks occur in a fixed sequence world-wide.

• Index Fossil – abundant, widespread, and lived for a short span of geologic time

• These fossils can be used to correlate and relatively date rocks in which they are found.

Which would make the

best index fossil?

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Absolute Age

Absolute Age

the numeric age of an object, or event, often stated in years before the present.

Ways to Determine Absolute Age

1. Rates of Erosion

2. Rates of Deposition

3. Varve Count

4. Radioactive Dating

#23 1. Rates of Erosion

By measuring how fast a river erodes, geologists can estimate how old it must be.

Only accurate for 10,000 – 20,000 years old.

Niagara Falls erodes at the rate of 1.3 meters per year

Erosion of Niagara Falls 2. Rates of Deposition

Geologists estimate that it takes about 1,000 years to deposit 30 centimeters of sedimentary rock.

This is not a highly accurate way of measuring age but can give useful estimates.

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3. Varve Count

Varves are sedimentary rock layers that occur annually.

Caused by glaciers freezing and thawing. Just like tree rings!

(Dendrochronology)

Ice core section showing annual

layers.

4. Radioactive dating: Half life

• the amount of time needed for half the

parent isotope to decay to daughter isotope

•Does Not Change- intensive property

Start 1 2 3 4

0 half-life half-life half-life half-life

100% 50% 25% 12.5% 6.25%

#24

How to calculate Half-lives

Find % of

parent

material

remaining

# of half-

lives

completed

Determine

amount of

time that

has past

Example:

The half-life of radon-222 is 3.8

days. How much of a 100g sample

is left after 15.2 days?

Find % of

parent material

remaining

# of half-lives

completed

Determine

amount of time

that has past