Notes: A Trip Through Geologic Time
pg. 95
A. Fossils are the preserved remains or traces of
living things
1. Form when living things die and are slowly
buried by sediments that slowly harden into
rock and preserve the shapes of the
organisms
2. Usually found in sedimentary rocks
3. Kinds of Fossils
a. Petrified Fossils – minerals replace all
or part of an organism; “turn it to stone”
b. Molds and Casts – most common
1.) mold – a hollow area in the sediment
in the shape of an organism
2.) cast – a copy of the shape of an
organism if minerals and sediment
seep into the empty space of a mold
c. Carbon Films – a thin coating of carbon
on rock
d. Trace Fossils – provide evidence of the
activities of ancient organisms, ex:
footprints
e. Preserved Remains – some processes
preserve remains with little or no change,
ex: tar, amber, freezing
4. The Fossil Record – provides evidence
about the history of life on Earth; shows
how different groups of organisms have
changed over time
B. Age of Rocks
1. Relative Age of rock is its age compared to
the ages of other rocks
a. law of superposition – oldest layer is at
the bottom and each higher layer is
younger than the layers below
2. Absolute Age of a rock is the number of
years since the rock formed
a. radioactive dating – during radioactive
decay, the atoms of one element decay
into atoms of another element
b. This shows the age of the oldest moon
rocks, so scientists infer that the Earth is
a little older than those rocks – about 4.6
billion years old
C. The Geologic Timeline – a record of the life
forms and geologic events in Earth’s history
1. Precambrian Time – where geologic
time begins, covers about 88% of Earth’s
history, ended 544 million years ago
2. Eras – the time between Precambrian
and the present are divided into three
long units
a. Paleozoic – began about 544 million
years ago and lasted 300 million
years; many animals were
invertebrates (no backbone) in this
era; “paloe-“ means ancient or early
and “-zoic” means life
b. Mesozoic – began about 245 million
years ago and lasted about 180
million years; the Age of the
Dinosaurs and mammals began to
evolve; “meso-“ means middle
c. Cenozoic – most recent era; began
about 65 million years ago and
continues to present day; the Age of
Mammals; “ceno-“ means recent
3. Periods – these are subdivided eras and
are characterized by what life existed
worldwide
4. Epochs – further subdivided periods of
the Cenozoic Era because the fossil
record of this era is more complete and
there are a lot more events to place in
sequence.
Notes: A Trip Through Geologic Time
A.
B.
C.
Fossils ____________________________________________________________________________
1.
Form when __________________________ and are slowly _____________________________
that slowly _________________________ and _________________________ of the organisms
2.
Usually found in __________________________________
3.
Kinds of Fossils
a.
Petrified Fossils – _________________________________________; “turn it to stone”
b.
Molds and Casts – __________________________
1.)
mold – a _________________ in the sediment in the _______________________
2.)
cast – a _____________________________________ if minerals and _________
_______________________________________ of a mold
c.
Carbon Films – a __________________________________ on rock
d.
Trace Fossils – provide _______________________ of ancient organisms, ex: footprints
e.
Preserved Remains – some processes ________________________________________,
ex: tar, amber, freezing
4.
The Fossil Record – provides evidence about ________________________________________;
______________________________________________________________________________
Age of Rocks
1.
Relative Age of rock is its ________________________________________________________
a.
law of superposition – ____________________________________________________
________________________________________________________________________
2.
Absolute Age of a rock is ________________________________________________________
a.
radioactive dating – during radioactive decay, the _____________________________
________________________________________________________________________
b.
This shows the age of ____________________________, so scientists infer that the
Earth is a little older than those rocks – _______________________________________
The Geologic Timeline – ______________________________________________________________
1.
Precambrian Time – where _______________________________, covers about _____
_____________________________, ended 544 million years ago
2.
Eras – the _____________________________________ are divided into ____ long units
a.
Paleozoic – began about 544 million years ago and lasted 300 million years;
____________________________________________ in this era; “paloe”- means
________________________ and “-zoic” means ______________
b.
Mesozoic – began about 245 million years ago and lasted about 180 million
years; the ___________________________ and ___________________ began to
evolve; “meso”- means __________________
c.
Cenozoic – __________________________; began about 65 million years ago
and _________________________; the ____________________________;
“ceno”- means __________________
3.
Periods – these are _____________________ and are characterized by ______________
___________________________________________
4.
Epochs – _______________________________________ because the ______________
of this era _____________________ and there are a lot more events to place in sequence.
Vocabulary
Lesson 1:
Paleontologist- scientists who study fossils
Evolution- the change in living things over time
Extinct- if an organism no longer exists and will never again live on Earth
Lesson 2:
Extrusion- lava that hardens on the surface and forms igneous rock; it is always younger than the rock
below it
Intrusion- magma that pushes into bodies of rock below the surface and hardens; it is always younger
than the rock layers around and beneath it
Fault- a break in Earth’s crust; it is always younger then the rock it cuts through
Index Fossil- used to help geologists match rock layers; must be widely distributed and represent an
organism that existed for a geologically short period of time
Unconformity- a gap in the geologic record; it shows where rock layers have been lost due to erosion
Lesson 3:
Radioactive decay- the atoms of one element break down to form atoms of another element
Half-life- the time it takes for half of the radioactive atoms to decay; the rate of decay of each
radioactive element never changes
Lesson 5:
Comet- a ball of gas, dust, and ice that orbits the sun
Lesson 6:
Invertebrate- animals without backbones (jellyfish, worms)
Vertebrate- animal with a backbone
Amphibian- an animal that lives part of its life on land and part of its life in water
Reptile- have scaly skin and lay eggs that have tough, leathery shells
Mass Extinction- many types of living things become extinct at the same time
Mammal-