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Notes on “Life & Geologic Time”
Earth/Space
S.W.B.A.T
• Explain how geologic time can be
divided into units
• Relate changes of Earth’s organisms
to divisions on the geologic time scale
• Describe how plate tectonics affects
species
Geologic Time
• Trilobites - segmented
marine animals that
went extinct
• Good index fossils
because they lived over
vast areas during
specific time periods
Video (2:54) “Science at
FMNH - Trilobite Evolution”
Geologic Time
• Geologic Time Scale – divisions based
mostly on extinction events in Earth’s
history
• Oldest rocks on Earth contain no fossils
• When no life is evident in the fossil
record other evidence such as
mountain-building is used to mark
geologic time
• Four major subdivisions from the longest time periods to the shortest are - eons, eras, periodsand epochs
• Eons - include the Precambrian and the Phanerozoic
Geologic Time
Geologic Time
• Precambrian – longest
geologic time period (3.9
billion years!) that shows no
fossil life at first
• Gradually simple marine
life-forms show in the rock
record
• Towards the end of the eon
more complex life evolved
Geologic Time
• Phanerozoic – shortest eon with an
abundance of fossils that shows more
complex life starting about 544 million
years ago
• This was also known as the “Cambrian
Explosion” when more complicated
marine organisms evolved hard parts
Video (3:18) “The Cambrian Explosion”
Geologic Time
• Eras - marked by
major changes in
worldwide life (usually
by mass extinctions)
• Eras include the
Paleozoic or “ancient
life”; Mesozoic
“middle” & the
Cenozoic “recent”
Geologic Time
• Periods - describe in
more detail the types
of life forms existing
worldwide
• Epochs - describe
regional (or more
local) life forms in
smaller divisions than
periods
Organic Evolution
• Species - a group of organisms that only
reproduce within that group
• Organic Evolution – the fossil record
shows that species change over time
• Almost all species clearly show change
over geologic time or millions of years
Organic Evolution
• Natural Selection - traits
within a species allow it
to adapt to changes in
the environment
• Charles Darwin – first
proposed natural
selection or “survival of
the fittest” with species
Organic Evolution
• If a species is unable to adapt to its
environment it will die out and not
pass on traits
• New species arise if enough different
traits are passed on where the
original species can no longer breed
with the new species
Organic Evolution
• Artificial selection -
human selection of
desired traits in
animals & plants
• Over time this has led
to many breeds of
animals (like dogs &
cats) and different
plants
Organic Evolution
• Trilobites – variety of
marine species that lived
for 200 million years in
shallow oceans
• Fossils show many
adaptations that allowed
the trilobites to survive
longer than the
dinosaurs
Organic Evolution
• Pangaea – all of Earth’s continents were
joined together in one huge landmass
• Trilobites finally died out when
Pangaea formed about 250 million
years ago
• The disappearance of shallow oceans
wiped out the Trilobite habitat
Video (1:18) “Pangaea and Into the Future”
(Computer Animation)
Class Activity
• According to Darwin’s theory of natural
selection, which animal species would
more likely survive in a polar climate –
• Cold-blooded animals with skin covered
by scales or –
• Warm-blooded animals with fur
(explain)
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