Bellringer 11/21/13
• What is a fossil?

Topic: Fossil Evidence of
Evolution
EQ: How do fossils form?

Take a look!

Evidence supporting evolution
• Fossil record
– shows change over time
• Anatomical record
– comparing body structures
• homology & vestigial structures
• embryology & development
• Molecular record
– comparing protein & DNA sequences
• Artificial selection
– human caused evolution

Fossil record
• Layers of rock contain fossils
– new layers cover older ones
• creates a record over time
– fossils show a series of organisms have lived on
Earth
• over a long period of time

What is a fossil?
• The preserved remains or traces of an organism that lived in the past
• Can be formed from a bone , tooth, shell, or other part of an organism

How do fossils form?
• Most fossils form when organisms that die become buried in sediments
(particles of soil and rock)

Fossil Formation
• Only the hard parts of an organism (bones, shells, and teeth) generally form fossils because the soft parts are broken down too quickly.
• Most fossils are formed when an organism is quickly buried by sediments.

Types of Fossils
• Mold – impression of an organism in a rock.
• Cast – a fossil copy of an organism in a rock.
• Trace Fossil – preserved evidence of the activity of an organism.
• Original Material – Tissues are preserved in ice, tar, and amber.

What are petrified fossils?
• A fossil formed when minerals replace all or part of an organism

How are mold and casts related to fossils?
• Mold – A type of fossil formed when shell or other hard part of an organism dissolves , leaving an empty space in the shape of the part
• Cast – A type of fossil that forms when a mold becomes filled in with minerals that then harden

What are trace fossils?
• Preserved evidence of the activity of an organism.

How else are remains preserved?
Original Remain
• Entire organisms, such as the huge elephantlike mammoths have been preserved in ice
• Bones and teeth have been preserved in tar pits
• Insects and other organisms can become stuck in sticky sap . The sap then hardens forming amber

How do you determine a fossil’s age?
• Relative dating
• Radioactive dating

What is relative dating?
• A technique used to determine which of two fossils is older
• Can only be used when the rock layers have been preserved in their original sequence

What is radioactive dating?
• A technique used to determine the actual age of a fossil
• The rocks that fossils are found near contain radioactive elements, scientists use these elements to determine decay
( half-life )

What are radioactive elements?
• Unstable elements that decay, or break down, into different elements

What is half-life?
• The time it takes for half of the atoms in a sample to decay
• Scientists can compare the amount of a radioactive element in a sample to the amount of the element into which it breaks down

What do fossils reveal?
• Fossils help scientists piece together information about
Earth’s past
• The millions of fossils that scientists have collected are called the fossil record

What is the Geological Time Scale?
• Scientist have used the ages of rocks and fossils to create a “calendar” of
Earth’s history that spans 4.6
billion years
• Scientists have divided this large time period into smaller units called eras and periods sometimes called the
Geologic Time Scale

What are the theories on how fast does Evolution Occur?
• Gradualism –
Evolution occurs slowly but steadily
• Punctuated
Equilibrium –
Species evolve during short periods of rapid change

When is a species extinct?
• A species is extinct if no members of that species are still alive