Paleontology
 The
study of past life
 Paleontologist – scientist who studies
fossils and plants from past life and
other recontructed past ecosystems,
study traces left behind by animals
and piece together the conditions
under which fossils were formed.
 Uniformitarianism – the idea that the
same geologic processes shaping the
Earth today have been at work
throughout Earth’s history
Relative vs. Absolute Dating
I. Relative dating – determining
whether an object or event is
older or younger than other
objects or events
A. Superposition
1. Older rocks are under
newer rock
2. Can only determine
relative time
B. Geologic column is an ideal
sequence of rock layers
that contains all the known
fossils and rock formations
on Earth arranged from
oldest to youngest.
II. Absolute Dating – the process
of establishing the age of an
object by determining the
number of years it has existed.
A. Radioactive decay – the
process in which a radioactive
isotope tends to break down into
a stable isotope of the same
element.
1. Radioactive atom has an
unstable nucleus that decays
a. Radiation is given off
b. Decay is at a constant rate
c. Decay material is formed
d. Half-life is the amount of
time for ½ of the
radioactive element to decay
2. Radioactive carbon dating
a. C-14 is present in all
living things
b. Used to date remains
***** Earth has been dated at
4.6 billion years
Fossils
III. Fossils – the remains or physical
evidence of an organism preserved by
geological processes.
A. Trace Fossil – a fossilized mark
that is formed in soft sediment by
the movement of an animal.
B. Index Fossil – a fossil that is
found in the rock layers of only one
geologic age and that is used to
establish the age of the rock
Measuring Geologic Time
IV. Geologic Time
A. Eras (largest divisions)
1. Precambrian – earliest,
4 billion years
2. Paleozoic – 345 million years
3. Mesozoic – 160 million years
4. Cenozoic – current, so far
65 million years
B. Eras are divided into
periods (except for
Precambrian)
C. Cenozoic periods are divided
into epochs
V. Geologic Eras
A. Precambrian
1. Earth forms including
seas & mountains
2. Few fossils of jellyfish,
worms, bacteria, algae,
& fungi
B. Paleozoic – 6 periods
1. Invertebrates most common
a. Trilobites
b. Brachiopods
2. Vertebrates – fish and
amphibians
3. Plants – ferns and trees in
swampy areas
Trilobite
Trilobite
Trilobite
Brachiopods
Brachiopods
Brachiopods
Eryops
Eryops
Eryops
Eryops
C. Mesozoic – 3 periods
1. Pangaea began to break
apart
2. Cycads & conifers evolved
3. “Age of the Reptiles”
4. Dinosaurs became extinct
Tyrannosaurus rex
Cycads
D.
Cenozoic – 2 periods
1. “Age of Mammals”
2. At least 4 ice ages