Bellringer 11/21/13 What is a fossil?

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

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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 elephant-like 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

Fossils help scientists piece together information about Earth’s past 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