Notes 7-2 and 8-2

Evidence and fossils

Evidence of evolution

• Similar body structures• Patterns of early development• Molecular structure• Fossils

Homologous Structures• The structure of the bones in a dolphin’s flipper, a

bird’s wing, and a dog’s leg is similar. Homologous bones are shown in the same color.

•

Can you tell the difference between these embryos?

Which one is the human?

Patterns of early development:

What about now?

Which ones look most alike?

Human Fish Tortoise Chicken Salamander Pig Rabbit Cow

Human Fish Tortoise Chicken Salamander Pig Rabbit Cow

How Do Fossils Form?• Most fossils form when organisms that die

become buried in sediments.

Changes Over Time• The fossils record

provides evidence about the history of life and past environments on Earth. In addition, scientists use fossils to study the rate at which evolution has occurred.

• Paleontologists are scientists who study fossils

Ages of Rocks

• Relative age- determine age of rock by comparing it to other rocks, does not provide a number

• Example: This rock is older than that rock

• Absolute age- determine actual age of rock in years

• Example: This rock is 10 million years old

The Position of Rock Layers• According to the law of superposition, in

horizontal sedimentary rock layers, the oldest layer is at the bottom. Each higher layer is younger than the layers below it.

Determining Relative Age

• To determine relative age, geologists also study extrusions and intrusions of igneous rock, faults, and gaps in the geologic record.

Determining Relative Age

• An unconformity occurs where erosion wears away layers of sedimentary rock. Other rock layers then form on top.

Using Fossils to Date Rocks• Index fossils must be widely distributed and

represent an organism who existed briefly• Index fossils are useful because they tell the

relative ages of the rock layers in which they occur.

The Geologic Time Scale• Because the time

span of Earth’s past is so great, geologists use the geologic time scale to show Earth’s history.

• A mass extinction known as the Cretaceous-Tertiary (K-T) extinction, ended the Mesozoic Era.

• It was possibly caused by a change in atmosphere due to an asteroid striking the earth

The Geologic Time Scale• Because the time

span of Earth’s past is so great, geologists use the geologic time scale to show Earth’s history.

• A Mass Extinction, known as the Permian extinction, ended the Paleozoic era.

• It was possibly caused by climate change due to the shifting of the continents