Docstoc

HISTORY OF LIFE ON EARTH

Document Sample
HISTORY OF LIFE ON EARTH Powered By Docstoc
					     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_Potassiu
m_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 present
Mesozoic: ~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 changes
ocean currents
carbon dioxide levels
......dramatic effects on the
evolution of life
Sea level
changes...
up to 200
meters
difference
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

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:1
posted:9/1/2012
language:Unknown
pages:28