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 Coloradol 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 First prokaryotes Cenozoic Era Mesozoic Era Paleozoic Era Precambrian Time First land plants First multicellular organisms First eukaryotes Radiation of mammals Accumulation of atmospheric oxygen

Human fossil record The most complete fossil evidence of a biped primate. 3 million yrs old, stood 3 ft tall Reconstructed skull

“Lucy” Facial recreation from fossil remains