17-1 The fossil record

Fossils

• Remains of once-living things

• Appear in a particular order

• Provide evidence for evolution.

Types of fossils

Leaf imprint

Shell casting

• archaeopteryx

Fossils may be bones or impressions in soft earth that hardened into stone.

Human: 20,000 yrs old Australia

Dinosaur Nat’l Monument, Utah

T Rex footprint

Relative dating

• Fossils are dated by the fossils + rocks around them.

• Gives an estimate of its age.

The Grand Canyon of the Colorado

ll

Layers contain marine fossils from a shallow sea. Where are the oldest fossils found?

Radioactive dating

• Uses radioactive elements in rock to find absolute age of fossils.

• Carbon-14 used for fossils ‘younger’ than 60,000 yrs.

Geologic time scale

• Precambrian: 88% of Earth’s history: unicellular life

• Paleozoic: invertebrates, vertebrates

• Mesozoic: dinosaurs• Cenozoic: Mammals,

birds

• Clock Model of Earth’s History

Copyright Pearson Prentice Hall

First humans

Firstprokaryotes

Cenozoic Era

Mesozoic Era

Paleozoic Era

Precambrian Time

First land plants

First multicellular organisms

Firsteukaryotes

Radiation of mammals

Accumulation of atmospheric oxygen

Human fossil record

The most complete fossilevidence of a biped primate. 3 million yrs old, stood 3 ft tall

Reconstructed skull

“Lucy”

Facial recreation from fossilremains