HISTORY OF LIFE ON EARTH

Physical conditions - last 4 billion years major changes:

•oxygen in atmosphere•climate change•ocean currents•sea level changes•continent movement•volcanism•meteorites

How do we know ages?Relative ages of rock layers (sedimentary):

their relative positions their embedded fossils

How do we know ages?

Absolute ages: radioisotopes

carbon 14 - half life of 5,700 y.less than 50,000 years

potassium 40 - half life of 1.3 b.y.the most ancient events

http://id-archserve.ucsb.edu/Anth3/Courseware/Chronology/09_Potassium_Argon_Dating.html

AGE DIVISIONS

Earth’s geological history is divided into eras (eg. Cenozoic) and periods (eg. Cretaceous). boundaries between units based on differences between their fossil biotas

Cenozoic: 65 m.y.a. to presentMesozoic: ~250-65 m.y.a.Paleozoic: ~550-250 m.y.a.Precambrian: ~550 m.y.a. to 4.5 b.y.a.

Crust movement

Continental drift: Throughout Earth’s history the continents have shifted, sometimes separating, at other times colliding.

Powered by radioactive decay within the Earth!

Climate change (temperature)

volcanism sea level changesocean currentscarbon dioxide levels......dramatic effects on the evolution of life

Sea levelchanges...up to 200 metersdifference

Meteorite 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)

Crater - in Yucutan Mexico

Meterorite or asteroid 10 miles in diameter

70% of living species wiped out

Debris blown into air caused dramatic cooling- nuclear winter

Global firestorm from methane gas released from ocean

The Fossil Record

Importance: Much of what we know about the history of life on Earth comes from the study of fossils.

The Fossil Record

Reveals broad patterns in the evolution of life.

Fossils show that many evolutionary changes are gradual.

Incomplete but getting better...

The Fossil Record

The Fossil Record

The Fossil Record

Life in the Remote Past

The fossil record for Precambrian times is fragmentary, but fossils from Australia show that many animals that evolved disappeared forever.

Ediacara Hills

Life in the Remote Past

Diversity exploded during the Cambrian period. The Cambrian Explosion. Why?

All modern phyla present ... and more

chinese fossil beds +

Burgess Shales

Life in the Remote Past

Hallucigenia

A phylum body plan that disappeared?

Rates of Evolutionary Change

Gradualism

Punctuated equilibrium

None? Coelacanth

... more later – molecular

clock

Rates of Evolutionary Change

Mass extinctions (5 so far)

99% spp. have become extinct, some during mass extinctions

major changes in flora and fauna

subsequent radiations after extinctions eg. Cenozoic radiations of modern mammals

Patterns of Evolutionary Change

Cambrian - all major Animal body plans (phyla) have evolved!

The Future of Evolution

The forces of evolution continue to operate today

eg. in humans: West Nile Virus, sexually transmitted diseases....

The Future of Evolution

Human intervention now plays an unprecedented role in the history of life.

Biodiversity crisis - the sixth great extinction