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6 Lesson 1 - Geologic Change Over Time NOTES

Geologic Change
Over Time
Both sudden & gradual
changes have affected
Earth’s history.
Evidence of past organisms….
processes preserve the remains of
organisms with little or no change
such as those organisms that become
trapped in
1. Amber (tree sap)
2. Ice
3. Asphalt or Tar
NOT preserved remains…
1. buried in rock (shells,
exoskeleton, bones left behind
2. petrified remains (minerals
replaces organism)
More evidence…
1. tracks
2. burrows
3. coprolite (animal dung)
Fossil Record
Information gathered by paleontologists is
called the fossil record which provides
evidence of:
• Environmental changes over time
• How life forms have changed over time
fossils – preserved remains or traces
of living things and are formed
when living things die and are
buried by sediments
paleontologist – scientists who
study, collect and classify fossils
mold – hollow area in the sediment which
shows the shape of an organism or a part
of an organism
cast – solid copy of the shape of an
Petrified Fossil
petrified fossil – fossils in which minerals
replace all or part of an organism
Carbon Film
carbon film – extremely thin coating on
Trace Fossil
trace fossil – provide evidence of the
activities of ancient organisms
Pangaea = a single landmass
(supercontinent) that broke apart
almost 200 million years ago
Evidence that support the landmass
theory are:
• The way rock types, mountains, and
fossils are now distributed on
Earth’s surface.
Evidence of Earth’s Climate
• Tree rings – If a tree ring is thick, it means it
grew well & temp was good. If it is thin, it means
there was a drought (lack of water).
• Sea-floor sediments – long cylinders of
sediment drilled from ocean floor. If microfossils are present, it means climate was warm or
• Ice – Ice cores are tubes of ice drilled out of
icecaps. Scientists study the “bands” in the ice
cores to see how much rain/snow fell.
Pg 88-89 #20-22
Pg. 90-91 Visual Summary/Lesson
Review PLUS Quizlet
The fossil record provides
evidence to support the theory of
• evolution – gradual change in living things over
long periods of time
• scientific theory – well-test concept that explains
a wide range of observations
• extinct – when an organism no longer exists and
never will again
On a post it note…
LINE 1 Write your name at the top
LINE 2 Write your birthdate
(including year)
LINE 3Write your age in years &
Lesson 2
Scientists can discover the order
of events in Earth’s history by
investigating surrounding
• relative dating– determine
whether an object or event is older or
younger than other objects or events.
Scientists can discover the order
of events in Earth’s history by
investigating surrounding
Law of Original Horizontality – gravity
causes sediment to be deposited in layers that
are horizontal.
Law of Superposition – in horizontal
sedimentary rock layers the oldest layer is at the
bottom; each higher layer is younger than the
layer below it
How are rock layers disturbed?
• Tilting – Earth’s forces move rock layers up or
down unevenly.
• Folding – bending of rocks by layers being
squeezed together
• Fault – break or crack in the Earth’s crust
(always younger than the rock it cuts through)
• Intrusion – igneous rock that forms when
magma is injected into rock then cools & hardens
• –
How are rock layers disturbed?
•Extrusion – when magma reaches the Earth’s
surface, cools and hardens (ex: basalt & obsidian)
•Unconformity – gap in the geological record
where some rock layers have been lost because of
Law of Crosscutting Relationships
• states that a fault or body of rock (such as an
intrusion/extrusion) must be younger than the
rock it cuts through.
See if you can put
the layers in order
from OLDEST to
To be considered an index fossil:
Must be widely distributed and represent
an organism that existed only briefly
Geologist use radioactive dating to
determine the absolute ages of rocks
• element – all the atoms of a particular type of
matter are the same
• radioactive decay – process by which one
unstable element breaks down into another
element that is stable
• half-life – time required for half of the unstable
element to decay
Geological Time Scale
Earth’s history is divided into units of
time that make up a geological time
scale which is divided into four major
• Eons – longest subdivisions; based on
abundance of fossils
• Eras – marked by significant worldwide
changes in the types of fossils present in rock
• Periods – based on types of existing life
globally at a particular time
• Epochs – divided periods characterized by
differences in life forms
Geological time begins with a long
span of time called Precambrian
Time, which covers about 88
percent of Earth’s history and
ended about 544 million years ago.
Scientists hypothesize that Earth
formed roughly 4.6 billion years
Precambrian Time
(4.6 billion-544 million years ago)
During the first several hundred million years of
Precambrian Time, an atmosphere, oceans and
continents began to form.
• very few fossils remain from this time
• Precambrian rocks have been buried, causing
fossils to be changed by heat and pressure
• most Precambrian organisms lacked hard parts
Earliest life form to appear was
cyanobacteria, or blue-green algae
which added oxygen to the
atmosphere through photosynthesis
Earth’s Eras
The time between Precambrian
Time and the present is divided
into three long units called eras:
• Paleozoic era – oldest era divided into six periods
• Mesozoic era – middle era divided into three
• Cenozoic era – youngest era divided into two
Paleozoic Era
544 million years ago to 245 million years ago
Early Paleozoic consists of the Cambrian and
Ordovician periods
• often called Age of Invertebrates
• continents covered by large, shallow inland seas
• no life existed on land; Ordovician period ended
with mass extinction
Paleozoic Era
Middle Paleozoic consists of Silurian and
Devonian periods
• often called Age of Fishes
• some invertebrates lived on land
• continents colliding forming mountain
Paleozoic Era
Late Paleozoic consists of Carboniferous and
Permian periods
• Age of Amphibians (reptiles evolved from
• continental collisions led to formation of Pangaea
• largest mass extinction occurred, reason under
Mesozoic Era
245 million to 65 million years ago
• often called the Age of the Reptiles
• contained the Triassic, Jurassic and Cretaceous
• dinosaurs dominated, small mammals and
birds appeared
• flowering plants (angiosperms) appeared
• Pangaea separated into continents, oceans
began to form
• mass extinction from large meteorite impact
scientists believe
Cenozoic Era
65 million to present
• Early in Tertiary period, India collided with
Asia to form Himalayas, Africa and Europe
collided to form Alps; Cascades and Sierra
Nevadas began to form in North America
• new grasses and flowering plants dominated
• mammals continued to evolve
• Homo sapiens, or humans appeared about
400,000 years ago – we live in the Holocene
epoch of the Quaternary period
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