Old and New Species Flashcards
How are fossils formed? (4)
The hard parts of an animal (bones, teeth, claws, shells) that don’t decay easily.
When an organism doesn’t decay because no oxygen or bacteria e.g. ice fossils.
When hard parts mineralise (are replaced by other minerals).
Traces of animals e.g. footprints, burrows, droppings
Why do fossils not give us a complete record of the history of life on earth?
First life forms were soft-bodied so decayed. Most organisms did not fossilise when they died or fossils were destroyed by geological activity. Many fossils are still to be found.
Describe the process of common fossilisation?
Animal dies, flesh rots. Skeleton covered by soil and clay. Over millions of years the biological material is replaced by rock
Causes for extinction?
Change in the environment e.g. new predators, diseases or new and more successful competitors, climate
What caused the dinosaurs to die out?
EITHER: Asteroid impact killed everything in its immediate surroundings and threw up dust that covered the sun so that reptiles (cold-blooded) and plants could not survive.
OR: Melting of sea ice flooded everything with cold water, triggered mass extinction over hundreds of millions of years
Why did marsupials evolve in Australia?
Some marsupials were geographically isolated when Australia split off from the other continents and while the rest of the world’s mammals developed more efficient reproductive systems, the marsupials became dominant
Define endemic
Where a species evolves in isolation and is found in only one place in the world
Define speciation
When natural selection of different alleles in an isolated population results in a change of features, to the extent that they can no longer interbreed with the original organisms.
Define genetic variation
When a population has a wide range of alleles that control their characteristics
Define natural selection
When the alleles that control the characteristics which help the organism to survive are selected
