Download Evolution Over Time

Change Over Time
Chapter 2 Lesson 3
What is natural selection?
• Dramatic changes have
occurred on Earth over
time: climate change,
forests have become
deserts, and seas have
dried up
• These changes affect
organisms within the
environments and they
must change in order to
survive
• Charles Darwin developed
a theory in the 1800s
about how organisms
change over time
• Population- is all of the
members of a singlespecies living in the same
geographic area
• Darwin noticed that there
were variations in the
populations (differences
among members of the
same species)
What is natural selection?
• Darwin’s theory is called
natural selection
• An organism with
favorable variations is
well suited to its
environment. It is more
likely to survive and
reproduce than others.
• Its variations will be
passed on to the next
generation
• “Survival of the Fittest”
is when the organisms
with the favorable traits
have survived.
• A horse is an animal that
has changed over time
• Ancestors walked on
several spread-out toes
that probably helped
them navigate swamps
and mud. As the land
dried, the horses
developed single, flat
hooves
What is natural selection?
• Throughout Earth’s
history, many
organisms have
emerged and many
have become extinct
• Extinct Species no
longer exist
anywhere on Earth.
• Species become
extinct because they
cannot adapt.
What is evidence of change
over time?
• Scientists know that environments have changed because the
history of change can be found in fossils
• Fossils- are any remains, traces, or imprints of organisms that
lived long ago.
• Fossils can be formed when minerals in the sediment preserve
bones, shells, or teeth of an animal
• Fossils can also be formed when an insect is trapped in tree
sap and the same hardens into amber
• Footprints can be made when an animal walks across wet
sand or mud and sediment quickly covers it and preserves the
print.
What Fossils tell us
• Provide clues that tell us
how environments have
changed
• For example: Scientists have
found fossils of an ancient
whale called Basilosaurus in
Mississippi which tells us
that Mississippi was once
covered by water
• Scientists can also predict
past climate of an area
• For example: Fossils of a
warm-climate animal found
in the arctic indicate that
particular areas climate was
not always artic like
• Fossils provide clues about
what organisms were like
in the past and how they
have changed (Smilodon)
• Earth’s history is marked by
geological and climate
change and have caused
some organisms to change
over time
• As environments change,
organisms will adapt, move
on, or die out
How has Earth changed?
• Earth’s history is
measured in long
stretches of time called
eras-each era is divided
into periods
• Precambrian- Earth first
became hospitable to
life. Few fossils have
been found
• Paleozoic- life became
abundant. Trilobites,
fish, insects, amphibians,
and reptiles appear
during this era
• Mesozoic- reveals the
appearance of dinosaurs,
mammals, birds, and
flowering plants. Rock
from this era indicate
that life became extinct
at the end of this era
• Cenozoic- the era we live
in. fossils show that
some early mammals
were very large. The
most recent ice age
occurred during this era.