Transcript Earth`s History

EARTH’S HISTORY
Creation of Sedimentary Rocks

Law of Original Horizontality:
 All
sedimentary rocks are originally deposited
horizontally or flat due to gravity and erosion.
Sedimentary rocks that are no longer horizontal have
been titled from their original position.

The sediment that forms sedimentary rocks is
deposited in flat layers one on top of the other.
Over time, the sediment hardens and changes into
sedimentary rock.
Cementation
• A major chemical digenetic change in which minerals
are precipitated in the pores of sediments, forming
cements that bind clastic sediments and rocks.
Lithification

The process that converts sediments into solid rock by
compaction or cementation
Question

Why are sedimentary rocks often formed in large,
flat layers?
 A.
Flat layers are formed whenever magma flows
outward from Earth.
 B. Sediments find flat surfaces on Earth to collect.
 C. Sediments usually collect on Earth’s surface as flat
deposits.
 D. Heat and pressure cause sediments to flatten out
into sheets.
Question

What must occur for loose sediments to become a
rock?
 A.
minerals from water flowing through them must
cement the sediments together
 B. magma flowing upward must cement the particles of
sediment together.
 C. heat and pressure squeeze the sediments closely
together and they begin to stick.
 D. sediments are magnetized by Earths magnetic field
and are attracted to each other.
Question

How do sediments carried by a river act when they
reach a lake?
 A.
they pile up at the far end of the lake.
 B. they spread out on the lake bottom
 C. they form a small mountain when the river meets the
lake.
 D. they dissolve in the lake water and disappear.
Relative Dating

Relative age of a rock is its age compared to the
ages of other rocks.
 Doesn’t

provide it absolute age, like a birthday.
Law of Superposition: geologist use to determine
the relative age of sedimentary rock layers.
 In
horizontal sedimentary rock layer the oldest layer is
at the bottom and each higher layer is younger than
the layer below it.
Relative Dating Continues

Geologists also use extrusions and intrusions of
igneous rocks to determine relative age
 Extrusions
is lava flowing across Earth’s surface. Each
layer added is younger then the previous.
 Intrusions is magma pushing into bodies of rocks. The
intrusion is always younger then the body of rock.
Relative Dating Continues

Geologist also use faults to determine relative age.
 Fault

is a break in Earth’s crust
A fault is always younger than the rock it cuts
through
Relative Dating Continues


Geologist use gaps in
the geologic record to
determine relative
age.
Unconformity:
 Where
a rock layer
has been eroded away
leaving a gap in the
geologic record
hays.outcrop.org
Relative Dating Continues


Geologist use index
fossils
Index fossil
Fossil must be widely
distributed and
represent a type of
organism that existed
only briefly.
 Help to match up
relative ages over the
Earth


Index Fossil Activity
Strata Diagram
Question

According to scientific assumptions, which rock
layers in the Grand Canyon will usually contain
older fossils? Those found:
 A.
nearer to the surface or the top of the canyon.
 B. at the edge of a cliffs.
 C. in rock layers located half way down the canyon.
 D. in the rock layers located deep in the canyon.
Fossil Formation

Molds and Casts

Mold: hollow area in sediments in the shape of an organism or par of an
organism





Minerals replace all or part of an organism
Done with mineral solution: minerals are dissolved in water
Petrified wood
Trace Fossils


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Cast: solid copy of the shape of an organism
Petrified Fossils: turned to stone


Hard parts such as shells or bones
Provide evidence of the activities of ancient organisms
Foot prints, burrows, etc..
Preserved Remains


Tar traps that preserved bones
Amber/sap: protects body from decay


Insects
Freezing preserve the most of the organism such as bones, hair, and skin.
Mold and Cast
Cast
Mold
petrifiedwoodmuseum.org
Petrified Fossils
animals.howstuffworks.com
Trace Fossils
answers.com
Butcher Fall 2008 Geo Trip
Preserved Remains
Frozen Mammoth: pinktentacle.com
Amber: dsc.discovery.com
Change Over Time


Paleontologists are scientists who study fossils
Fossils Record



Fossils allow us to piece together what past environments may have
looked like.



Provides evidence about the history of life and past environments on
Earth.
Also shows how different groups of organisms have changed over time.
Climate
Changes in Earth’s surface: swamps, lakes, dry deserts, etc…
Older rocks contain similar fossils, where younger rocks contain fossils
similar to our time.



Fossils record show us that organism have changed or evolved over time.
Evolution: is the gradual change in living things over long periods of time.
Extinct: organism is not living anymore.
Question

What evidence do scientists have that supports the
idea that Earth’s surface has changed over time?
 A.
fossils of rainforest plants in areas that are deserts
today.
 B. rocks that came from outer space
 C. modern plants and animals that look like ancient
organisms.
 D. climates in some places on Earth that are different
than other places.
Question

In the dry and hilly region of southeast Utah, many
fossil remains have been uncovered. Trilobite casts,
petrified bones of alligators, and preserved dinosaur
footprints, were all found in the same location, but in
different rock layers. What do these fossil remains tell
about the history of this region?
A. this area was a gathering place for a variety of
animals.
 B. ancient flooding in this region washed fossil remains into
this area.
 C. the Earth’s surface and climate has changed over time.
 D. this region has always had hot, dry climates.

Question

In a region of Wyoming covered by rolling hills,
small lakes, and dry gulches, a petrified shark’s
tooth was found. What does this fossil indicate
about the geological history of this region?
 A.
it was once covered with a vast freshwater lake.
 B. it was once covered by a swamp or marshland.
 C. it was once covered by an ocean.
 D. it has always had the same geography as it has
today.
Question

Which of the following is a typical location where a
bone or shell could become petrified?
 A.
buried in the sand of a desert.
 B. submerged in shallow water or mud.
 C. in the frozen soil of the arctic.
 D. covered with leaves in a tropical rainforest.
Question

Why do recently deposited rock layers contain
fossils more like animals that are alive today?
 A.
Rocks that are deposited over time may have
moved.
 B. Animals cannot form fossils if they are alive today.
 C. Rock layers do not change quickly.
 D. The fossils are the most recent ancestors of today’s
animals.