3How do we know ages? Relative ages of rock layers (sedimentary): their relative positionstheir embedded fossils
4Absolute ages: radioisotopes How do we know ages?Absolute ages: radioisotopescarbon 14 - half life of 5,700 y.less than 50,000 yearspotassium 40 - half life of 1.3 b.y.the most ancient events
5AGE DIVISIONS Cenozoic: 65 m.y.a. to present Mesozoic: ~250-65 m.y.a. Earth’s geological history is divided into eras (eg. Cenozoic) and periods (eg. Cretaceous).boundaries between units based on differences between their fossil biotasCenozoic: 65 m.y.a. to presentMesozoic: ~ m.y.a.Paleozoic: ~ m.y.a.Precambrian: ~550 m.y.a. to 4.5 b.y.a.
14Meteorite collisions also have changed conditions on Earth. cause of abrupt mass extinction at the end of the Cretaceous period (65 m.y.a)-- iridium-- Yucatan crater (180 km diameter)
15Crater - in Yucutan Mexico Meterorite or asteroid 10 miles in diameter70% of living species wiped outDebris blown into air caused dramatic cooling- nuclear winterGlobal firestorm from methane gas released from ocean
16The Fossil RecordImportance: Much of what we know about the history of life on Earth comes from the study of fossils.
17Reveals broad patterns in the evolution of life. The Fossil RecordReveals broad patterns in the evolution of life.Fossils show that many evolutionary changes are gradual.Incomplete but getting better...
21Life in the Remote Past Ediacara Hills The fossil record for Precambrian times is fragmentary, but fossils from Australia show that many animals that evolved disappeared forever.Ediacara Hills
22Life in the Remote Past Burgess Shales Diversity exploded during the Cambrian period. The Cambrian Explosion. Why?All modern phyla present... and morechinese fossil beds +Burgess Shales
23Life in the Remote Past Hallucigenia A phylum body plan that disappeared?
24Rates of Evolutionary Change GradualismPunctuated equilibriumNone? Coelacanth... more later– molecular clock
25Rates of Evolutionary Change Mass extinctions (5 so far)99% spp. have become extinct, some during mass extinctionsmajor changes in flora and faunasubsequent radiations after extinctions eg. Cenozoic radiations of modern mammals
26Patterns of Evolutionary Change Cambrian - all major Animal body plans (phyla) have evolved!
27The Future of Evolution The forces of evolution continue to operate todayeg. in humans:West Nile Virus,sexually transmitted diseases....
28The Future of Evolution Human intervention now plays an unprecedented role in the history of life.Biodiversity crisis - the sixth great extinction