Transcript Evolution_Evidence of Evolution_4

Evidence of Evolution
The Fossil Record

Fossil Record: all the fossils that have been
collected around the world
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Fossils-Geology
– Remains of ancient life
– Different layers of rock formed at different times
 Comparing the old rocks from new rocks, scientists could
document the Earth had changed over time

Darwin saw the fossils as a record of history
 Species had come into being, lived, and then vanished
Transitional Fossils
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Transitional Fossils: Fossils that document
intermediate stages in the evolution of modern
species from organisms now extinct

Explains how animals we see today came from
animals now extinct
– Gaps in fossil record still exist
 Perfect conditions (sedimentary rock, etc.)
 Parts of species will never fossilize (soft tissue)
Geographic Distribution

Geographic Distribution: species distributed due
to geography (islands, mountain ranges)
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Decent with modification from common ancestor
– WHAT???

Species came (descended) from a common
ancestor but due to changes (modification)
became new species
– Darwin’s finches
But what about Species that look
alike but aren’t related??

Species that live in similar environments
may resemble each other
– Even if they do not decent from a common
ancestor
– How?

Natural Selection
– Exposed to same pressures, adapt the same
Homologous Structures
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Homologous Structures: Structures
that have different mature forms but
develop from same embryonic tissues
– Animals look different as adults but they all
developed from the same tissues in embryo

Further suggests that organisms have a
common ancestor
Vestigial Structures

Vestigial Structures: structures reduced
in size because they no longer serve a
function
– Only traces (vestiges) of the structure still
exist
Embryology
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Early stages of life are very similar

Embryonic cells (first cells) develop in
similar orders to produce the tissues and
organs of all vertebrates

Grow to produce homologous structures
Radioactive Dating

Radioactive Dating: Dating species based on
the half-lives of radioactive elements
– Half-life: length of time for half of the radioactive
atoms to decay in a sample

Radioactive elements decay into nonradioactive
elements over time
– The amount they have decayed can determine how
old that organism is
Carbon-14 vs. Carbon-12

Carbon-14 is taken up while a species is
living
– It is converted to Nitrogen-14 and evaporates

Determining how much Carbon-14 had
decayed can help scientists determine
when an organism lived