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Earth’s History
The Earth is estimated to by
around 4.5 billion years old.
– Most information about the age of the
Earth comes from studying the rocks in the
crust.
– We can aso study fossils.
• Explore the following link for more info on fossils:
http://www.ucmp.berkeley.edu/education/explorations/tours/fossil/guide/guide.html
Rocks
Evidence of Change Life
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Fossils
Ice cores
Composition of sedimentary rocks
Faults
Igneous rock formations
Fossils
• provide important evidence of how life and
environmental conditions have changed
• the preserved remains or traces of an
organism that lived in the past
• different types of fossils based on how they
were formed
Types of Fossils
• Mold fossil – forms when sediments bury an
organism and the sediments change into rock;
the organism decays leaving a cavity in the
shape of the organism
• Cast fossil – forms when a mold is filled with
sand or mud that hardens into the shape of
the organism.
Types of Fossils
• Petrified fossil (permineralized fossil) – forms
when minerals soak into the buried remains,
replacing the remains, and changing them into
rock.
• Preserved fossil – forms when entire
organisms or parts of organisms are prevented
from decaying by being trapped in rock, ice,
tar, or amber
Types of Fossils
• Carbonized fossil – forms when organisms or
parts, like leaves, stems, flowers, fish, are
pressed between layers of soft mud or clay
that hardens squeezing almost all the
decaying organism away leaving the carbon
imprint in the rock.
• Trace fossil – forms when the mud or sand
hardens to stone where a footprint, trail, or
burrow of an organism was left behind.
Ice Cores
• Ice cores- cylinders of ice that are drilled out
of glaciers and polar ice sheets.
• When snow falls it carries with it the
compounds that are in the air at the time.
• A record of the atmosphere at the time that
the snow creating the ice layers fell.
Sedimentary Rock
• 75% of the rocks on the Earth’s surface.
• form on the surface of the Earth, anywhere
that sand, mud, or other types of sediment
collect.
• Scientists can gain an understanding of Earth’s
climate, biological, and geologic history by
examining the contents of different layers of
sedimentary rock.
Principles of Stratigraphy
1. Uniformitarianism
The processes that formed rocks in the past are
the same as those we observe on Earth today.
Principles of Stratigraphy
2. Law of Original Horizontality
Sediments are deposited in horizontal layers
that are parallel to Earth’s surface.
Geological processes change the angle
AFTER the rocks have been deposited.
Principles of Stratigraphy
3. Law of Superposition
The oldest layers of rock are on the bottom. The
youngest are on top.
Principles of Stratigraphy
4. The Law of Cross-Cutting Relationships
Any igneous rock or fault must be younger than the
rock layer it is in.
Principles of Stratigraphy
5. Unconformities
Gaps in the rock record.
Formed when part or all of a layer is missing.
Principles of Stratigraphy
6. Correlation
The matching of rock layers from different locations.
• Index fossils are fossils that are known to come
from a specific time period. (Very useful in
correlating rocks on different continents)
Igneous Rock
• Sedimentary rock layers can be disturbed by
igneous rock when molten rock forces it way
up through the layers above it.
• Sedimentary rock layers must be there first, so
igneous rock intrusions are younger
• Igneous rock is always younger than rock
layers it cuts through.
Faults
• a break in the rocks that make up the Earth’s
crust that is formed due to the movement of
rock on either side of the fault
• two main types of faults involve dip slips and
strike slips.
Dip Slips
• two pieces of land change their vertical
position compared to one another
• one side of the fault is higher than the other
Strike Slips
-two pieces of land move horizontally
Two Ways to Determine Rock Age
1. Relative dating-compares ages of
different rock layers and fossils.
2. Absolute dating gives the actual age of
the rock.
Radioactive dating-used for absolute dating.
Radioactive Dating
• Radioactive decay- unstable elements in the
Earth’s crust will decay into smaller elements at
a constant and predicable rate
– The half-life-time it takes for one half of a
sample to decay.
Radioactive Dating
• Since radioactive decay is constant, amounts
of original and decayed elements are
compared.
• Determines the age of the substance.
• Parent atom = radioactive
• Daughter atom = stable atom
Relative Dating
• The Earth’s surface has changed over time.
• Geologist’s use the rock record to interpret
past events.
• Stratigraphy -study of structure, fossil content,
origin, history, and age relationships of rock
formations.
Plate Techtonics
• The movements of Earth’s continental and oceanic plates have
caused mountains and deep ocean trenches to form and continually
change the shape of Earth’s crust throughout time.
• Sea level changes over time have expanded and contracted
continental shelves, created and destroyed inland seas and shaped
the surface of land.
• Sea level changes as plate tectonics cause the volume of the oceans
and the height of land to change, as ice caps on land melt or
enlarge and/or as sea water expands when ocean water warms and
cools.
• The evolution of Earth’s living things is strongly linked to the
movements of the lithospheric plates.
• The movements of the plates cause changes in climate, in
geographic features such as mountains, and in the types of living
things in particular places.
Geologic Time
The geologic time scale is
divided into eras marked
by important events in
the rock record.
Eras can be divided into
periods, and periods can
be further divided into
epochs.
• Listed youngest to oldest
Geologic Time
• Precambrian Era:
– Oldest and Longest (about 4 billion years)
– Little is known about this era. The Earth formed during this
era, and the first life developed.
• Paleozoic Era:
– Organisms became more complex; Biodiversity exploded
– The first mass extinction occurred at the end of this era.
• Mesozoic Era:
– Age of the Dinosaurs
• Cenozoic Era:
– Age of Mammals
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
studying rock layers and fossils world wide.
• Radioactive dating helped determine the
absolute divisions in the time scale.
Divisions of Geologic Time
• Eras are subdivided into periods...periods are
subdivided into epochs.
Era
Period
Epoch
E + P = EP
FOUR Eras…
• PRECAMBRIAN – 88% of earth’s history
• Paleozoic (ancient life)
– 544 million years ago…lasted 300 million years
• Mesozoic (middle life)
– 245 million years ago…lasted 180 million years
• Cenozoic (recent life)
– 65 million years ago…continues through present day
Precambrian Era
• 5 major events occurred during this era:
1. The formation of the Sun and light.
Creation of
2. Earth
3. atmosphere through volcanic outgassing.
4. Oceans
5. Life
Precambrian Era
• Began with simple life forms such as bacteria and
simple algae.
• There was a rise of simple organisms such as jellyfish
and sea worms by the end of the era.
• Few fossils because the life forms were soft-bodied
and had no hard skeleton.
Paleozoic Era (Ancient Life)
• The Cambrian period is the 1st period of the Paleozoic
Era. “Age of the Trilobites”
• Explosion of life in the oceans began during this era.
• Most of the continents were covered in warm,
shallow seas.
– Invertebrates were dominate - Trilobites
– Fish emerged
– Fish led to the arrival of amphibians
• The end of the Paleozoic era is called the “Age of Amphibians”
– Early land plants including mosses, ferns and cone-bearing
plants.
– The early coal forming forests were also formed during this
time.
Trilobites
• Lived in Earth’s ancient seas
• Extinct before the dinosaurs
came into existence
• Cambrian Period is know as
the “Age of the Trilobites”
• Body has 3 sections
• Good index fossil
Paleozoic Era
Much of the limestone quarried for building and industrial
purposes, as well as the coal deposits of western Europe
and the eastern United States, were formed during the
Paleozoic.
The Cambrian (beginning) opened with the breakup of the
world-continent Rodinia and closed with the formation of
Pangaea, as the Earth's continents came together once
again.
This event is thought to have caused the climate
changes that led to mass extinction event.
The Appalachian mountains were formed during this time.
Paleozoic Era
• At the end of the Paleozoic, the largest mass
extinction in history wiped out approximately
90% of all marine animal species and 70% of
land animals.
– Possible causes of this Mass Extinction Event
• Lowering of sea levels when the continents
were rejoined as Pangaea (convergent
boundary)
• Increased volcanic activity (ash and dust)
• Climate changes – cooler climate
Brachiopods
• Marine animals that resemble clams.
Early Fish
Early fish did not have jaws.
Some species of sharks were
in existence at this time.
Mesozoic Era – Middle Life
• At the beginning of this era the
continents were joined as Pangaea.
• Pangaea broke up around the middle
of this era.
• Reptiles became the most abundant
animals because of their ability to
adapt to the drier climate of the
Mesozoic Era.
– Skin maintains body fluids
– Embryos live in shells
Mesozoic Era
• 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.
– The mammals were small, warm-blooded
animals. Hair covering their bodies.
• These characteristics help them survive in
changing environments.
Mesozoic Era
• The main plant life of this time were
Gymnosperms or plants that produce
seeds, but no flowers.
– Pine Trees
• Flowering plants appeared during the
END of this era.
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.
Mesozoic Era – Mass Extinction Event
Asteroid or Comet collides with Earth.
Huge cloud of smoke and dust fills the air
Blocks out sunlight
Plants die
Animals that eat plants die
Animals that eat plant-eaters die.
Mesozoic Plants
Flowering plants evolved
towards the end of the
Mesozoic Era.
Cenozoic Era – Recent Life
• Began about 65 million years ago and continues
today!!!!!
– Climate was warm and mild.
– Marine animals such as whales and dolphins evolved.
• Mammals began to increase and evolve
adaptations that allowed them to live in many
different environments – land, air and the sea.
– Grasses increased and provided a food source for
grazing animals
• Many mountain ranges formed during the
Cenozoic Era
– Alps in Europe and Himalayas in India; Rocky Mountains
in the USA
Cenozoic Era
• Growth of these mountains may have
helped to cool down the climate
– Ice Ages occurred late in the Cenozoic Era
(Quaternary Period).
• As the climate changed, the animals had to
adapt to the rise and fall of the oceans
caused by melting glaciers.
• This era is sometimes called the
“Age of Mammals”
Cenozoic Era
• Marine animal examples:
– Algae, Mollusks, Fish and Mammals
• Land animal examples:
– Bats, Cats, Dogs, Cattle and Humans
– Humans are thought to have appeared around 3.5
million years ago (during the most recent period –
Quaternary).
• Flowering plants were now the most common
plant life.
Today…
• Today we are in the Holocene Epoch of the
Quaternary Period of the Cenozoic Era.
Which unit is the largest?
Which unit is the smallest?