Unit A Ch1 L3 Organisms from the past

Report
Chapter

Lesson 3
1
 Students
will:
◦ Explore how skeletons are used to
help compare organisms.
◦ Describe evidence scientists consider
to compare and classify organisms of
the past.
◦ Describe reasons organisms can
become extinct.

Fossil
◦ Any evidence of
an organism that
lived in the past.
◦
◦ Fossils are often
skeletons
preserved in rock.
Fossils preserved in rock.
◦ When someone
discovers a new
fossil, they might
ask themselves:
 “How would this
organism fit into
today’s
classification
system?”

They might
compare the fossil
with bones of
similar animals
living today.
◦ Evolution
 Change in living things over time.
◦ Scientists must consider that organisms
change over time.
 For example, scientists have traced the
ancestors of the modern horse back to 60
million years.
◦ One way in which they accomplished this
difficult task was by comparing the fossils of
skulls, teeth, and leg bones.
Based on fossil
evidence, scientists
think that the
Hyracotherium is an
ancestor of all
horses.
What similarities and
differences do you
see?
How did the animals’
appearance change?
◦ Another way in which
fossils can be
compared is by
determining their age,
or “how old” the fossil
is.
◦ One way in which this
can be determined is
by studying the rock
layer in which a fossil
is found.

Looking at other
fossils found in the
same rock layer
tells that the
organisms lived at
about the same
time.

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The youngest
fossils are in the
youngest layer,
which the top layer.
The oldest fossils
are in the oldest
layer, which the
bottom layer.

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The younger fossils are
found in the upper layers.
Layer A is younger than
Layers B, C, & D.
Layer B is older than Layer
A, but younger than Layers
C & D.
Layer C is older than
Layers A & B, but younger
than D.


Do you think the
organisms on this
slide have anything
in common?
Even though each
animal uses these
bones differently,
the bones are
arranged in similar
ways.


Scientists use the
evidence shown by
limb bones when
they classify
organisms.
Some of their
findings are
surprising.

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
Whale bones are more
closely related to humans
than to sharks.
Look at the flipper bones.
They are much more like
human arm bone than a
shark’s fin.
Whales and humans are
both mammals.
◦ Another clue to
identifying
similarities among
organisms comes
from before they
were even born.
◦ Embryo: an
undeveloped animal
or plant.
◦ Each has backbone or
spine.
◦ They both have gill
slits and a tail.
◦ These features
suggest that
organisms are related
and they are both
vertebrates.
◦ An embryo changes
before it is ready for
the world.
◦ Some features are lost
in certain animals as
the embryo grows.
◦ Birds do not have gill
slits when they are
born.
◦ Extinct
 No longer alive on Earth.
◦ To help classify extinct animals, scientists
compare the fossil embryos with each other
and with modern embryos.
Extinct
Tasmanian
Tiger
◦ Another clue that organisms might be related
can be found in “leftover” structures.
◦ Humans don’t need a tail, but a human adult has
a tailbone at the end of the spine.
 Some snakes have tiny hip and limb bones.
 A baleen whale has small, useless hip
bones.
◦ These useless bones are clues that help
classify organisms into groups.
◦ Baleen whales are probably related to
organisms that have and use those bones.

Many organisms have become extinct over
the years.
◦ Some scientists believe that 99 out of every 100
species that have ever lived on Earth are extinct.

Mass extinctions
◦ It is when many different species died out at about
the same time.
◦ Judging from fossils, there have been many mass
extinctions.
◦ The best-known mass extinction is that of the
dinosaurs.
◦ They died out about 65 million years ago, along
with more than half of all other animals and plant
species.
Different theories of mass extinctions
◦ Giant meteorite
 It hit the Earth and caused the extinction of the
dinosaurs.
 Evidence to support this theory was found by Walter
Alvarez and his father, Dr. Luis Alvarez.
Different theories of mass extinctions
◦ Giant meteorite
 The meteorite would have created great clouds of dust
that blocked sunlight.
 Without sunlight, plants could not have had the food they
needed to survive.
 Without plants, plant-eating dinosaurs would have died.
 Without them, meat-eating dinosaurs would have died.
Different theories of mass extinctions
◦ Volcanoes
 Other scientists believe that many huge volcanoes
erupted, creating great clouds of dust.
 This theory would have had the same effect as a
giant meteorite.
Different theories of mass extinctions
◦ Deadly Diseases
 Other scientists believe that dinosaurs spread deadly diseases as
they moved about Earth.
◦ It is possible that a combination of these events caused the
extinction of the dinosaurs.
People and Extinction
 People play an important in the extinction or
endangerment of animals.
 We:
◦ use pesticides and chemicals which destroys
places where animals live today.
◦ destroy their resources.
◦ also hunt and fish.



Learning about the past helps us learn about
the present.
Know how organisms have changed over time
and who their ancestors were helps us to
better understand the history of life on Earth.
It also helps us classify living and extinct
organisms.

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