•YES…an example: cockroaches
• Fossils- scientists can infer the
structure of ancient organisms.
Fossils show that organisms that
lived in the past are very different
than organisms that live today.
• Similarities in early development
•Similarities in Body Structure
• An organism’s body structure is its basic body
plan, such as how it’s bones are arranged.
• Similar structures that related species have
inherited from a common ancestor are known
as homologous structures.
• Along with fossils, early development
patterns, and body structures, scientists
also use similarities in DNA to show how
organisms are related to one another.
• Genes are made of DNA, DNA is made of a
sequence of nitrogen bases. The more similar
the DNA sequence, the more closely related
the species are.
• In most cases, evidence from DNA has
confirmed conclusions based on fossils,
embryos, and body structure.
• Sometimes new evidence changes
scientists hypothesis.
• Branching trees are used to show how
scientists think different groups of
organisms are related.
• A new species can form when a group of
individuals remains isolated from the rest of its
species long enough to evolve different traits.
• Rivers or other bodies of water, a volcano, or
a mountain range can separate group
members.
Meet, “Sue.” She was discovered in
1990 in South Dakota and resides in the
Field Museum in Chicago.
• *Most fossils form when organisms that die become
buried in sediment.
• Some remains that become buried in sediments are
actually changed to rock. These are called petrified
fossils.
• Sometimes the remains dissolve and a hollow space is
created, this space is called a mold. This mold
becomes filled with hardening minerals, forming a
cast.
• Some organisms have been preserved in substances
other than sediment…like ice. Ex. mammoths
• Scientists can determine a fossil’s age
in two ways: relative dating and
radioactive dating.
•Relative dating is used to determine
which of two fossils is older. This is
done by looking at the layers of rock
in which the fossil was found.
•Radioactive dating allows scientist to find
the actual age of a fossil. The rocks that
fossils are found near contain radioactive
elements, which are unstable that break
down or decay into different elements.
The half-life is the time it takes for half
of the atoms in the radioactive element
to break down. By comparing the
amount of radioactive element in a
sample, scientists can calculate the age
of the rock, thus the age of the fossil.
• The millions of fossils that scientists have
collected are called the fossil record.
• A species is extinct if no members of that
species are still alive. Most of what scientists
know about extinct species comes from the fossil
record.
• The fossil record provides clues on how and
when new groups of organisms evolved. This
calendar of Earth’s history is called the
Geological Time Scale.
• What causes mass extinctions?
•Scientists are not sure. They hypothesis
major climate changes caused by an
asteroid or volcanic eruption.
• At what rate does evolution occur?
•Scientists are not sure of this either. One
theory is called gradualism. Evolution
occurs slow and steady