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The History of Life
Chapter 14
How the Earth Was Made:
The Birth of the Earth Video
I. Paleontologists
A. Scientists who
study ancient life
1. Kinds of
2. Ancient
3. Geography
II. Early History of Earth
A.Very hot
B. Volcanoes
spewing lava
and gases
C. Little oxygen in
the atmosphere
but lots of CO2,
nitrogen and
water vapor
II. Early History of Earth
Earth Cools
-lava cools (forms
-rains for millions
of years (forms
-3.8 bya
III. Fossils
A. Sedimentary rocks contain fossilsclues to the past
B. Oldest rocks 3.9 BILLION years old.
III. Fossils
C. The Fossilization process
III. Fossils
D. Mold (empty space)
E. Casts (minerals fill a
space left by decayed
F. Trace fossils (indirect
G. Petrified
H. Amber preserved (quickly
trapped in sap & hardened)
I. Frozen (preserved in ice)
V. The Age of a Fossil
A. Relative Dating
1. Determined by dating the
rocks in the layer above and
below the fossil
a. Newspaper example
2. An estimate of age
V. The Age of a Fossil
B. Radiometric Dating
1. Determination of how many of the
original atoms are left in the rock.
a. Atoms decay at a steady rate
2. Half-life- Time needed for ½ the
atoms to decay
a. If the fossil’s half-life is 2 million
years, when ½ of its atoms are gone
it will be 2 million years old.
V. The Age of a Fossil
3. Scientists use potassium-40
to date the oldest rocks and
carbon-14 to date younger
a. Draw example on board
4. Errors can occur if the rock
has been heated (atoms are
lost or gained).
VI. The Geologic Time Scale
A. Four Eras
1. Precambrian
2. Paleozoic
3. Mesozoic
4. Cenozoic
VII. Life in the Precambrian
(4600-543 MYA)
A. Earth’s formation
B. Prokaryotes
1. Cynobacteria-like
2. Stromatolites
C. 1.8 BYA eukaryotes
D. 87% of Earth’s history
VIII. The Paleozoic Era
543 MYA – 245 MYA
A. Cambrian
explosion of life!
1. Worms, sea
stars, arthropods,
2. 400 MYA, ferns
& early seed plants
End of the Paleozoic
B. Largest mass
1. 90% of marine
species extinct
2. 70% of land species
IX. Mesozoic
245 MYA – 66 MYA
A. Triassic period
1. Mammals (small)
2. Dinosaurs
3. Fern forest
B. Jurassic period
1. Dinosaurs
2. Modern birds
evolved from birds of
this period
End of the Mesozoic
C. Cretaceous Period
1. New Mammals
2. Flowering Plants
D. Mass extinction of the
1. 66% of all living
species extinct
2. Evidence of meteorite
collision (Mexico)
E. Pangaea broke apart
66% died
34% survived
End of the Mesozoic
See “Owen’s Dinosaur Video”
X. The Cenozoic Era
66 MYA – present
A. Mammals
B. 30 MYAprimates
C. 200,000 years
ago, modern