How Fossils are formed (3)
3) GRADUAL REPLACEMENT BY MINERALS
Teeth, shells, bones etc. dont decay easily
They are eventually replaced by minerals as they decay
They form a rock-like structure, exactly the same shape as the original hard part
The surrounding sediment turns to rock, but the fossil satys distinc
The remains of organisms from many years ago, which are found in rocks.
Provide the evidence that organisms lived millions of years ago
How Fossils are formed (1)
1) CASTS AND IMPRESSIONS
An organism is buried in a soft material like clay
The clay hardens around it and it decays, leaving a cast of itself
E.g. animal burrows, plant roots
Footprints cna be pressed into materials when soft, leaving an impression when it hardens
How Fossils are formed (2)
2) PRESERVATION WHEN NO DACY HAPPENS
Amber and tar pits
No oxygen or moisture; microorganisms can't survive
Too cold for decay microbes to work
Too acidic for decay microbes
What is a species?
A group of similar organisms that can reproduce to give fertile offspring.
What is speciation?
The development of a new species.
When does speciation occur?
When 2 populations of the same species become so different they can no longer reproduce to give fertile offspring.
Reasons for Extinction
1) Environment changes too quickly (e.g. destruction of habitat)
2) New predator
3) New disease
4) They can't compete with other species for food
5) Catastrophic event
6) A new species evolves (speciation)
Theories of how life began
There are various hypotheses, but no one really knows
1) The first life forms came into existance in a primordial soup
2) Simple organisms arrived here on comets and more complex organisms evolved from these
These can't be supported - lack of valid and reliable evidence
Because some scientists believe many early organisms were soft-bodied, and soft tissue tends to decay away completely
So the fossil record is incomplete.
Fossisl formed millions of years ago may have been destryoed by geological activity
How does Speciation occur? (2)
6) So the alleles that control the beneficial charateristics are more likely to be passed on to the next generation
7) After some time the majority of the popultion will show this charateristic
8) Eventually individuals from the different populations will have changed so muh that they won't be able to breed with each other to produce fertile offspring
9) The 2 groups will have become seperate species
How does Speciation occur?
1) Isolation; population of the same species are seperated
This can happen due to physical barrier
E.g. floods, earthquakes or mountain ranges can cause barriers that geographically isolate individuals from the main popualtion
2) Conditions on either side of the barrier will be slightly different e.g. climate
3) Because the conditions are different on either side, different charateristics will become more common in each population, due to natural selection
4) Each population will show variation because htey have a wide range of alleles
5) Individuals with charateristics make them better adapted to their environment
This gives them a better chance of survival , so they are more likely to reproduce