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)