Transcript Slide 1

History of Earth and its landforms…
8.E.2.1 and 8.E.2.2
Create a brainsplash in your notebook for
the term “Fossil”.
What is a fossil?
• Fossil: preserved remains or traces of an organism
that lived in a past life
– Give clues to…
• the diversity of living things over the history of
the Earth
• Past climate and surface changes on Earth
• Changes that have occurred within organisms
over time
What are the different types of fossils?
• Types of fossils are based on how they were
formed.
• Formation process varies depending on where
and under what environmental conditions
• Mold Fossil
– Sediments bury an organism and change into rock
– Organism decays leaving a cavity in the shape of an
organism
• Cast Fossil
– Forms when a mold is filled with sand or mud that
hardens into the shape of the organism
• Petrified fossil
– Minerals soak into the buried remains, replacing the
remains, and changing them into rock
• Preserved Fossil
– Entire organism or parts of organisms are prevented
from decaying by being trapped in rock, ice, tar, or
amber
• Carbonized Fossil
– Forms when organisms or parts, like leaves, stems,
flowers, fish are pressed between layers of soft mud
or clay
– Mud/clay hardens, squeezing almost all of the
decaying organism away, leaving the carbon imprint
on the rock
• Trace Fossils
– Form when mud or sand hardens to stone where a
footprint, trail, or burrow of an organism was left
behind
Mr. Parr- Fossils
What are the different types of rock?
• Sedimentary rock: rock formed by deposition
of sand, clay and other pieces of rock that are
compacted together under pressure
• Metamorphic Rock: formed under the surface
of the earth from the metamorphosis (change)
that occurs due to intense heat and pressure
(squeezing).
• Igneous Rock: formed when magma (molten
rock deep within the earth) cools and hardens.
What is the fossil record?
• Millions of fossils have been collected and
studied
• Fossil Record- the complete body of fossils
that shows how species and ecosystems
change over time
– Extinction
– How new life forms appeared
– Certain organisms could only live in specific
environments or under particular climate
conditions
What is relative age?
• The age of one object compared to the
age of another object
• Does not tell exact age
• Relative age of rocks and fossils can be
determined two ways:
–Ordering of rock layers
–Index fossils
What is the law of superposition?
• Each layer of rock is deposited on top of
other layers
• Law of Superposition: oldest rocks lie on the
bottom, youngest rocks lie on the top of an
undisturbed sequence of sedimentary rock
– Used to read rock layers
The Law of Superposition- Grand Canyon
How do scientists use the ordering of rock
layers for relative dating?
• Scientists infer that the relative age of the rock or
fossil in the rock is older if farther down in rock
layers
• Relative dating is best when the rock layers have
been preserved in their original sequence
– Tectonic plate motion can distort the layers
– Youngest layers are not always found on top
What are index fossils?
• Index Fossils
– Organism must have lived during a short part of
Earth’s history
– Many fossils of the organism must be found in rock
layers
– Must be found over a wide area of earth
– Organism must be unique
• The shorter time period a species lived, the
better an index it is.
• Can be used to find the relative age of rock
layers
What are trilobites?
• A group of hard-shelled animals whose body had
three sections
Trilobites
– Lived in shallow seas
– Became extinct about 245 million years ago
• Key example of index fossil
– If a trilobite is found in a rock layer, it can be compared
to trilobites found in other rock layers to estimates the
age of the rock layer in which it was found.
What is radioactive decay?
• Universe if full of naturally occurring
radioactive elements
– Radioactive decay- unstable atoms breakdown
over time into stable isotopes or other elements
• Molten Rock cools, trapping radioactive atoms
inside.
• Radioactive atoms always break down at the
same rate and into the same other form
What is half-life?
• The rate of change of a radioactive element if
measured in half-lives.
– Half-life: the length of time it takes for half of the
atoms in a sample of a radioactive element to
change from an unstable form to another form.
What is radiometric dating?
• Scientists measure the quantity of unstable atoms
in rock and compare to stable quantities.
• Elements with half-lives of millions to billions of years
are used to date rocks.
– Uranium 235 has a half life of 704 millions years. It
changes to lead 207.
– Carbon 14 is used to date remains of things that were
once alive.
• Half-life: 5730 years
• Absolute dating
– scientists find an absolute age of the rock because they
know the rate at which the radioactive elements decay
What is the geologic time scale?
• Divides earth’s history into
intervals of time defined by
major events or changes on
Earth
• Earth is 4.6 billion years old
– Eon: largest unit of time, 4
Eons in Earth’s history
– Era: Eons are divided into eras
– Period: eras are subdivided
into periods
– Epoch: periods of 2 eras are
further divided into epochs
What are the “eras” on the geologic time scale?
• At the end of each era, a mass extinction occurred.
• Precambrian era
– Creation of earth- 4.6 BYA
– Major events
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Formation of the sun and light
Creation of earth
Creation of the atmosphere through volcanic out-gassing
Creation of oceans
Creation of life
– Began with simple life forms: bacteria and algae
– Rise of simple organisms ( jellyfish, sea worms) by the end of
the era
– Few fossils because of soft bodied organisms
• Paleozoic Era
– Began with early invertebrates  vertebrate fish
arachnids and insects  amphibians reptile
– Early land plants (mosses, ferns)
– End of era- seed plants
– Mass extinction cause most marine invertebrates and
amphibians to disappear.
• Mesozoic Era
– Reptiles were dominant, dinosaurs
– Small mammals and birds appeared
– Flowering plants, and other mammals appeared
towards the end of the era
– Mass extinction caused dinosaurs to become extinct
• Cenozoic Era
– New mammals appeared, others became
extinct
– Diversity of life increased
– Flowering plants became more common
– Humans are part of the most recent period
What are ice cores?
• Cylinders of ice that are drilled out of glaciers
and polar ice sheets
• Help to understand how climate has changed
– Snow falls and carries compounds that are in the air
with it
– In areas where the temperature is rarely above
freezing, layers of ice build up
– In the layers is record of the atmosphere at that time
How are sedimentary rocks used to
determine geological history?
• 75% of the rocks on Earth’s surface
• Studying the contents give us information
• Igneous rock can disturb sedimentary rock
– Molten rock forces its way up through the layers
above it
– Forms younger igneous rock layers within and across
sedimentary layers
What is a fault?
• 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.
• Occur when there is a movement of tectonic plates
– Earthquakes
• Dip Slip Fault: land changes their
vertical position
• Strike Slip Fault: land changes
their horizontal position
What is the Theory of Plate Tectonics?
• Earth’s continental and oceanic plates
continually change the shape of Earth’s crust
throughout time.
• Using the theory, scientists can study and predict
geologic events.
• Evolution of Earth’s living things is strongly
linked to the movements of Earth’s plates.
Additional Information
• Absolute (radioactive) Dating Measurement of the known rates of decay of
radioactive materials that an object contains in order to determine the age of
the object
• Index Fossils Fossil known to have lived in a particular geologic age that can be
used to determine the date of the rock layer in which it was found
• Law of Superposition Law that states that in undisturbed rock layers that newer
layers will be deposited over older layers
• Relative Dating Determining the age or order of things from the past or past
events without knowing or calculating the actual age
• Sedimentary rock Rock formed by deposition of sand, clay and other pieces of
rock that are compacted together under pressure
• Uranium Radioactive heavy metal that is an abundant source of nuclear
energy that has 14 known isotopes used in radioactive dating