Biology - B2.6 - Old and New Species

HideShow resource information

B2.6.1 - The Origins of Life on Earth

  • Earth ~4500million years old, life began ~3500million years ago - debate whether life developed due to Earths conditions or simple life forms arrived from another planet
  • Date rocks - fossils in rocks - know when they exsisted
  • Fossils formed in different ways:
    • hard parts of animals that don't decay easily, eg. bone
    • parts of organisms that haven't decayed due to conditions, eg. ice
    • organism parts replaced by other materials, eg. minerals, as they decay
    • preserved traces of organisms eg. footprints
  • Most dead organisms don't leave fossils - inappropriate conditions
  • Many lifeforms were soft bodied so few traces were left behind
  • Traces left were likely to have been destroyed by geological activity
1 of 4

B2.6.2 - Exploring the Fossil Evidence

  • Fossil record is incomplete, but can learn from fossils we do have - some organsims have changed a lot, some only a little and some are extinct - completely died out
  • Extinction caused by many things, but always involve changed circumstances:
    • new disease kills members of species
    • environment changes over geological time
    • new disease introduced
    • new predator may evolve or introduced to an area
    • new competitor may evolve or introduced to an area
    • single catostrophic event may destroy habitat
    • natural changes in species over time
2 of 4

B2.6.3 - More About Extinction

  • Environmental changes - biggest influence on species survival
  • Climate change - influence what species survive - cold be well adapted to hot climate and become extinct in an ice age - insufficient food or can't breed - could become to hot, cold, wet or dry and reduce food supply
  • Fossil evidence - mass extinctions on global scale - many species die out over several million year - habitat destroyed by catastrophic events or environment change dramitcally due to collision of asteriod with Earth
  • Reason for dinosaurs extinction is unknown - suggestions include:
    • asteriod collision caused huge fires, earthquakes, landslides and tsunamis - dust rose, masking sun, causing darkness and lower temperatures - plants couldn't grow and temperatures fell
    • sea ice melting - slower process - water temperatures fell, killing plankton - limiting food supply
3 of 4

B2.6.4 - Isolation and the Evolution of New Specie

  • New species arise from exsisting ones, if a group becomes isolated
  • Goelogical isolation - occur if island separates from mainland, river separates two areas - mountain ranges or old craters cause isolation
  • Organisms left on an island exposed to different environment, predators or food - natural selection occurs - different characteristics beneficial
  • If populations can't interbreed they belong to two separate species
  • New species occur following geographical isolation - each population has range of alleles controlling characteristics - genetic variation
  • Natural selection occurs - alleles controlling characteristics helping organism to survive allow organism to survive and breed
  • If environment, competitors, predators or food supply is different, populations evolve differently
  • Speciation occured when populations can't interbreed
4 of 4


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Evolution, extinction and natural selection resources »