CHAPTER 6C

• EVIDENCE OF THE PAST

Paul Sereno……1995

• Found dinosaur skull 1.5 m long

• Paleontologist – use fossils to reconstruct the past

Fossils

• Trace remains or imprints of living organisms that are preserved by geological processes.

The Age of Fossils

• Relative Dating – estimating the age of rocks or fossils by their depth in sedimentary rock

• Absolute Dating – measuring the time it takes for an unstable atom to decay

Absolute Dating

The Geologic Time Scale

Mass Extinctions

• When a species dies out

• Scientists feel that the dinosaurs died out so quickly because of a fast changing environment

The Changing Earth

Precambrian Time

• Grand Canyon Bottom

• 4.6 billion yrs ----- 542 million yrs

• Life began here

• Atmosphere was CHAOTIC

• NO Oxygen early on

• 1st prokaryotes

Precambrian Time

• 2nd – Cyanobacteria

• Photosynthesis and oxygen -- ozone

• NOW life on earth surface

• 1 billion yrs ago

• Multicellular organisms

• eukaryotes

Paleozoic Era

• 542 million -- 251 million

• WATER – sponges, corals, snails, squids, trilobites, fish, sharks

• LAND – ferns, mosses, horsetails, conifers

• NO flowering plants

• Insects

• Salamander-like animals

Paleozoic Era

• END of REPTILES and winged insects

• MASS EXTINCTION – 90% of water species are gone

Mesozoic Time

• 251 million – 185.5 million

• “Middle Life”

• Age of Reptiles– Dinosaurs– Birds– Conifers– Flowering Plants

Mesozoic Time

• EXTINCTION ??????????

Cenozoic Time

• 65 million – today

• Recent Life

• Age of Mammals– Mastodons– Saber toothed cats– Camels, sloths, small horses– Humans

Cenozoic Time

• ICE AGE

• Organisms moved to Equator to live or become extinct