B2 - Speciation Flashcards
Name the types of different fossils (4)
Rock fossils
trace fossils
amber fossils
mummification
What are fossils?
The remains of organisms from many years ago.
Describe the formation of rock fossils.
Shells, teeth and bones can become fossilised after they are covered by layers of sedimemt.
Describe the formation of trace fossils.
Footprints or burrows can show evidence. A living thing steps onto mud which is then turned into rock when it gets covered by sediment.
Describe mummification.
If the conditions for decay are absent then microbes cannot decay properly.
ie. dry, cold, lack of oxygen.
Describe the formation of amber fossils.
Small animals and insects were trapped in liquid tree sap which then solidifies. No oxygen is present so no decay occurs.
Why is the fossil record incomplete?
Why didn’t some organisms leave fossils behind?
We often have no record of early organisms because they were SOFT BODIED and decayed. The ones that did fossilise may have been DESTROYED due to geological effects (eg. erosion).
Many organisms had the right conditions for decay so didn’t fossilise.
What can fossils tell us?(4)
1) How new organisms arise.
2) How new species are formed.
3) How species have changed over time.
4) About plants and animals which become extinct.
State 5 factors which cause extinction.
CATASTROPHIC EVENT - organisms may be unable to adapt quick enough after catastrophic events such as volcano eruptions, asteroid impacts. eg. Dinosaurs.
NEW PREDATORS - eg. Dodo
NEW COMPETITORS - eg. Red Squirrel vs Grey
NEW DISEASE - new strain or mutation of existing disease eg. Tasmanian Devil.
ENVIRONMENTAL CHANGE - such as acid rain or global warming. eg. mammoths, polar bears.
What is speciation?
The process where new species are formed or existing species split off into one.
What defines a species?
They have the same number of chromosomes.
They are able to produce fertile offspring.
Describe the process of speciation.
1) Original population shows variation.
2) A physical barrier separates/isolates the population.
3) Conditions on either side of the barrier are different.
4) Individuals with the best characteristics survive and breed and pass these useful alleles onto their offspring.
5) Eventually they will become so different they’re a separate species because they can no longer breed with eachother.
