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
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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
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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
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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 alloworganism to survive and breed
If environment, competitors, predators or food supply is different, populations evolve differently
Speciation occured when populations can't interbreed
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