Download Modern Geology

What is the age of
the Earth?
Most geologist agree
the Earth is about 4.6
billion or 4600 million
years old.
If each grain of corn represented 1 year it
would take 2 full silos of corn to equal 4.6
billion years. It is just hard for our minds to
imagine how large this number is!!
Modern Geology
James Hutton is credited as being the Father
of Modern Geology. In his book Theory of the
Earth he stated that the key to understanding
the processes we observe today -erosion and
deposition- do not change over time. This
Uniformitarianism
theory is called
the processes we see today have been at work
throughout all the Earth’s history.
Change happens gradually!!!
Grand Canyon Uniformitarianism
Modern Geology
During Hutton’s time, the early 1700’s,
most scientists thought the earth was only
several thousand years old and that
erosion and deposition could not have had
enough time to shape the earth. They
believed in Catastrophism –principle
that states that geologic
occurs suddenly!!!
change
Meteor Crater Arizona
Volcanic Pinatubo and Mt. St. Helen
Modern Geology
Charles Lyell in 1830’s reintroduced Hutton’s
theory of uniformitarianism. He challenged the
theory of catastrophism and the scientific
community accepted that geologic change
comes gradually. Stephen Gould
challenged both theories in the late 1800’s. He
stated that both can occur in shaping geologic
change. This is the currently accepted
theory.
Paleontology
Paleontology is the study of past
life. Scientists who study past life
are called paleontologist.
Fossils are the data paleontologist
use in their study of past life.
Rock Cycle
Sedimentary Rock
Sedimentary rock can be formed from all three
types of rocks if eroded and deposited in layers
and over time “cemented” together. Examples
are sandstone, limestone, siltstone, and
conglomerate.
Sedimentary rock is the rock that
fossils are found in . Metamorphic and
Igneous are too hot and too much pressure to
allow a fossil to be formed and preserved.
Igneous Rock
Igneous rock can be formed from any of the
three rock types. Igneous is formed by melting
rocks into magma. If the magma stays
underground and is cooled slowly it is called
intrusive igneous rock and has small crystals. If
the magma reaches the surface it is called
extrusive igneous and the crystals are large
because of rapid cooling. Examples are granite,
basalt, and gabbro.
Metamorphic Rock
Metamorphic rocks are created
from any of the three rock types.
They are formed under intense
heat and pressure. Examples are
Schist, marble, slate, shale, and
gneiss.
Law of Superposition
States that in a series of
sedimentary rock younger
rocks and sediment lie on
top of older rocks and
sediment unless the layer
have been disturbed.
Earth’s History
Geologist rely on fossils and rocks to
help them determine the events of the
past. Determining whether an object
or event is older or younger than
other objects or events is called
relative dating. It does not use
numbers; just OLDER or YOUNGER to
determine the relative order.
Law of Superposition
Rock Layers
Geologist assume that layers of rock
and sediment are laid down
(deposition) in horizontal layers
and if they are not horizontal
something disturbed them after
they were formed.
Rock Layers
Disturbing Forces
Many rock sequences are disturbed by forces
within the Earth. Scientists use a model called
Geologic Column
the
to place
rock and sediment layers from the top
(youngest) to the bottom (oldest). It is and
ideal sequence of rock layers that
contain all known fossils and rock formations
on Earth arranged from the youngest to the
oldest. Page 437
Geologic Column
How Rock Layers are Disturbed
1. Fault- a break in a body of rock along which
one block slides up or down relative to
another. Footwall/Hanging wall
2. Intrusion- molten rock squeezes into the
cracks in the rock layers. Path of least
resistance. Veins of gold form this way.
3. Folding- rock layers bend and buckle because
of the Earth’s internal forces.
4. Tilting- Earth’s internal forces slant the rock
layers at an angle to the horizontal.
Normal Fault Hanging Wall Slides
Down due to shear forces
Reverse Faults the Hanging Wall is
Pushed Up due to Compression Force
Strike Slip Fault Slides Side to Side
San Andreas Fault Strike Slip Fault
Normal Fault
Reverse Fault
Intrusions
Intrusion
Intrusion
Folding
Folding
Tilting
Tilting
Rock Layers
Faults and intrusions cut across
the rock layers (rock layers were there
first) therefore they must be younger
than the rock layers they cross.
Folding and tilting are always
younger (rock layers were there first)
than the rock layers they cross.
Unconformity
A missing rock layer(s) in a sequence of
rocks is called a Unconformity. They represent
Missing Time: Missing Time
Unconformities are generally caused by erosion or
non-deposition.
When a geologist comes across a unconformity
they must decide whether the “missing layers” ever
existed or were somehow removed (wind, erosion,
uplifting of the land).
Page 439 shows examples.
Types of Unconformities
1. Disconformity is formed where part of a
sequence of parallel rock layers is missing.
Represents 1000’s of years of lost time.
2. Nonconformity is horizontal sedimentary
layers lying on top of eroded metamorphic or
igneous rock. Represents millions of years of lost
time.
3. Angular unconformity is found between
horizontal layers of sedimentary rocks that have
been tilted or folded. Represents millions of
years of lost time.
Disconformity
Nonconformity
Law
of
Superposition
With the Law of Superposition we expect
to find fossils further down in earth are
older just like the rock or sediment layers
with the exceptions of Anticlines and
Synclines.
Anticlines have the oldest rock in the
middle because it has been pushed up.
Syncline have the youngest rocks in the
middle because it has been pushed down.
Earth’s History
Geologist rely on fossils and rocks to
help them determine the events of the
past. Determining whether an object or
event is older or younger than other
objects or events is called relative
dating. It does not a have a specific
date (number) attached to it, only is it
younger or older than another object.
Absolute Dating
Is the process of establishing the age of an
object by determining the number of years
it has existed. Radiometric dating is the
most common method of absolute dating.
Atoms of the same element have the same
number of protons but different numbers of
neutrons are called Isotopes. Most are
stable, however there are some that are
unstable and are radioactive.
Radioactivity
Radioactive decay occurs at a very stable rate
(always at exactly the same rate) and can be used
to predict age of objects. As the unstable isotope
breaks down (parent isotope) a stable isotope is
produced (daughter isotope). Scientists can
compare the amount of parent isotope to the
daughter isotope to determine age of objects.
The more daughter isotope present the older the
object is. Radiometric dating is the ratio of
daughter material to parent material.
Half Life
Is the time it takes for one half of the parent
material to become daughter material.
1 HL= 50% parent 50% daughter
2 HL= 25% parent 75% daughter
3 HL= 12.5% parent 87.5% daughter
4 HL= 6.25% parent 93.75% daughter
So if the HL of an isotope is 10,000 years how
old is the object if 4 HL have occurred?
If the initial sample mass is 1
kg after 3 half lives how much
parent material is there and
how much daughter material
is there?
Step 1. 1kg divided by 2 is .5 kg
Step 2. 0.5 kg divided by 2 is 0.25 kg parent
material and 0.75 daughter material.
Step 3. 0.25kg divided by 2 is 0.125 kg parent
material and 0.875 kg daughter material.
Step 4. 0.125kg divided by 2 is 0.0625 kg parent
material and 0.9375 kg daughter material.
Step 5. 0.0625 kg divided by 2 is 0.03125 kg
parent material and 0.96875 kg daughter
material.
Types of Radiometric Dating
1. Potassium-Argon- Potassium 40 has a HL
of 1.3 billion years. Used to date rocks
older than 100,000 years old.
2. Uranium-Lead- Uranium 238 has a HL of
4.5 billion years. Used for rocks greater
than 10 million years old.
3. Rubidium-Strontium- Rubidium 87 has a
HL of 49 billion years. Used for rocks
greater than 10 million years old.
Carbon-14
Carbon-14 has a HL of 5730
years. Used to date objects that
have lived within the last 50,000
years. When an plant or animal
dies carbon -14 is no longer
absorbed and its ratio to carbon12 decreases (more carbon-12).
Trilobite the fossil of the Cambrian period
• Many different species that lived at different geologic
times. Excellent index fossil
• Ammonite . The second most famous index
fossil. Many different species lived at different
times throughout geologic time.
Cast Brachiopods
Mold Brachiopods
• Brachiopods the third most famous index
fossil, a type of bi-valve shell organism.
Fossil
Is the remains or physical evidence of
an organism preserved by geological
processes. Fossils are most often found
in sedimentary rock due to being
deposited in layers with out heat and
huge pressures of igneous and
metamorphic rock. Bones and shells are
the most often found fossil and rarely
soft tissue is found except as(frozen).
Where are Fossils Found?
1. Amber or types of hardened tree sapusually associated with small organisms so
the whole organism is preserved totally.
2. Petrifaction- the process in which
minerals replace an organisms
tissues(Petrified wood).
3. Asphalt or Tar pits- a sticky material that
traps an organism and it is preserved in
the material( La Brea Tar pits in California).
Where are Fossils Found?
4. Frozen- it slows down decay so there is almost no
decomposing (Wooly Mammoth).
5. Rock- sedimentary rock (igneous and metamorphic
destroys the organism before it can possibly
become a fossil).
6. Carbonized- Layers of soil squeeze the decaying
organism almost completely away except for the
carbon imprint is left on the hardened rock.
Examples are leaf, stems, or flowers.
Petrified Wood
La Brea Tar Pits
Carbonized leaf fossils
Earth Core Samples
Trace Fossils
Are naturally preserved evidence of
animal life or activity.
1. Footprint2. Burrows- living quarters of some animals.
3. Coprolite- preserved animal dung.
Mold- cavity or impression in a rock where a plant
or animal was buried.
Cast- an object that is formed when sediment fills
or is poured into a mold and becomes rock.
Trace Fossils
Mold versus Cast
Why Fossil Records are Incomplete
1.
2.
3.
4.
Most organisms never become a fossil.
Many fossils are yet to be discovered.
Not all dead organisms become fossils.
Only a small fraction of organisms in Earths
history become fossils.
Ocean fossils on mountain tops suggest
uplift. Tropical fossils in Antarctica suggest
continental drift.
Index Fossils
Are fossils of organisms that lived
during a relatively short well defined
period geological time period. They
must be found in rock layers
throughout the world.
Index fossils can be used to establish
the age of different rock layers and
other fossils in them.
Index Fossils
Trilobites- Lived from 540 mya to
248 mya with many different types
of species that lived in many parts
of the world. One of the most used
index fossils. Generally considered
very old fossils.
Index Fossil
Brachiopods- lived from 480
mya until about 350 mya. An
important Index fossil. It had
many species that lived many
places in the world.
Index Fossils
Ammonites- Lived from about
385 mya until 65 mya. A very
important Index fossil that had
many species that lived for
short time periods in many
places over the world
Transitional Fossil
Transitional fossils are fossils that
are intermediate between the
ancient organism and fossils of the
more modern organism.
Transitional fossils shows the
evolutionary adaptations of
organisms over time.
Ice Cores
Ice cores are samples of ice that have
been drilled out of ice layers. The
purpose of ice cores is to study the
atmospheric gases present at
specific times in history. By studying ice
cores scientist predict what the climate
was like on the continents.
Antarctica has ice cores for 750,000 years
scientist can observe.
Ice cores
Glaciation
Time periods on Earth where ice began to
cover large parts of the continents surface.
Generally recognized as Ice Ages. During
these times ocean levels are decreased
significantly because the water that
evaporates is trapped on land. During the
last ice age the ocean levels were 400 feet
less than they are today.
Marine fossils on Mountain tops, same
fossils on different continents, or Tropical
fossils in Antarctica
Ocean fossils on mountain
tops suggest uplift.
Tropical fossils in Antarctica
suggest continental drift.
Similar fossils on several
continents suggest continents
were connected in the past
Pangaea and Panthalassa
Pangaea was the huge landform
made of all the continents on the
earth connected together. It
dates back to about 250mya
Panthalassa was the huge all
connected ocean that
surrounded Pangaea.
Pangaea looks like a huge jig-saw puzzle that fits
neatly together. Continental drift allowed similar
fossil types to be found on different continents.
Mass Extinctions
Most paleontologist agree at least 5 mass
extinctions have occurred in earth’s history.
Extinctions are the death of
every member of a species.
The reasons for mass extinctions are: Global
cooling from A) Ash from volcanic activity B)
Asteroid of meteor impact C) Ice age from
too little sunlight.
Mass Extinctions
1. End of the Ordovician period 65 % of all
species.
2. End of the Devonian period 70% of all
species.
3. End of the Permian period 96% of all species.
4. End of the Triassic period 70% of all species.
5. End of the Cretaceous period 65% of all
species.
Naming Organisms-Taxonomy
Kingdom
Phyla
Class
Orders
Families
Genera
Species
Kitchen Patrol Cooks Orders For General Staff
Geologic Time
Scientist estimate the
earth to be about 4.6
billion years old which
is the same as 4600
million years old.
Precambrian
This time represents 7/8 of all Earth’s history.
All life forms during this time were very simple
algae, bacteria, or multi-celled invertebrates
(sponges, jellyfish, sea pens). The first mass
extinction recorded on Earth occurred at the
end of this time. The Cambrian Period begins
after the Precambrian and starts the Cambrian
Explosion of Life where many different forms of
life began to populate the Earth.
Geologic Time
Geologic time is broken down into 4
divisions.
EONS- There are 4 eons. The largest
division of time.
ERAS- There are 3 eras. Includes 2 or
more periods.
PERIODS- There are 12 periods.
EPOCHS- there are 7 epochs
EONS
Hadean- 4.6 to 3.8 billion years ago.
Archean- 3.8 to 2.5 billion years ago.
Proterozoic- 2.5 billion ago to 543 mya
Phanerozoic- 543 mya to present
There is not a set number of years for
an eon.
Eras
Paleozoic- 543 million to 248 million years.
Called the era of “ OLD LIFE.”
Mesozoic- 248 million to 65 million years.
Called the era of “Age of Reptiles.”
Cenozoic- 65 million years to present.
Called the era of the “Age of Mammals.”
There is not a set number of years
in a ERA
Periods
There are 12 periods divided across the three eras.
Paleozoic era includes Cambrian, Ordovician, Silurian,
Devonian, Mississippian, Pennsylvanian, and Permian
periods.
Mesozoic era includes Triassic, Jurassic, and Cretaceous
periods. In the Triassic dinosaurs begin, Jurassic is
“Golden Age of Dinosaurs”, and in the Cretaceous
dinosaurs become extinct).
Cenozoic era includes Tertiary and Quaternary periods.
There is not a set number of years in a PERIOD.
Epochs
All epochs occur in the Cenozoic era
(the most recent time from 65
million years to present). Epochs
include Paleocene, Eocene,
Oligocene, Miocene, Pliocene,
Pleistocene, and Holocene.
There is not a set number of years in an
EPOCH.
What time do we live in?
We live in the
Phanerozoic eon, in the
Cenozoic era, in the
Quaternary period, and
the Holocene epoch.
Phanerozoic Eon
The Phanerozoic Eon
means “VISIBLE LIFE”
and is divided into three
Eras; Paleozoic,
Mesozoic, and Cenozoic.
Paleozoic Era
Paleozoic means “Age of OLD
LIFE.” 543 million years ago to 248
million years ago. It ended with
the largest mass extinction on
Earth. 96% of all creatures on
earth became extinct.
Mesozoic Era
Mesozoic means “AGE OF REPTILES.”
Dinosaurs ruled the Earth (Triassic,
Jurassic, & Cretaceous Period). At the
end of the Mesozoic Era 65% of all
species became extinct. Supposedly
ended with a asteroid hitting the Earth
in the Gulf of Mexico.
Cenozoic Era
Cenozoic means “AGE OF
MAMMALS.” It begins 65 million
years ago. Mammals have
regulated body temperature, bare
young alive, have body hair, feed
offspring milk, and care for the
offspring for an extended time.