Fossils and Extinction Flashcards
What are fossils?
The remains of organisms from many years ago, which are found in rocks. Fossils provide the evidence that organisms lived ages ago.
In what 3 ways can fossils form?
1) Gradual replacement by minerals
2) Casts and Impressions
3) Preservation in places where no decay happens
Things like [ ], [ ], bones etc. which don’t decay easily, can last a long time when buried
Teeth, shells
Describe how mineral replacement works
Teeth, bones, shells etc. are eventually replaced with minerals as they decay forming rock-like substances shaped like the original hard part
The surrounding sediments also turn to rock, but the fossil stays distinct inside the rock
Describe the conditions where castings happen
When organisms are buried in a soft material like clay.
How are castings made?
The dead organism is buried by a soft material. The clay later hardens around it and the organisms decays, leaving a cast of itself
An animal’s [ ] or a plant’s [ ] can be preserved as casts
Burrow
Roots
How does an impression happen?
Things like footprints can be pressed into these materials when soft, leaving an impression when it hardens
What is amber?
A clear yellow ‘stone’ made from fossilised resin
Describe preservation
1) In amber and tar pits there’s no oxygen or moisture so decay microbes can’t survive
In glaciers it’s too cold for the [ ] to work
decay microbes
Why can’t microbes survive in peat bogs?
They’re too acidic for decay microbes
Name some conditions where decay microbes can’t survive
1) Amber
2) Peat bogs
3) Glaciers
4) Tar pits
What do fossils show?
How today’s species have evolved
Name some theories for how life started
primordial soup
under the sea
Comets
Briefly describe the ‘comet’ theory
Simple organic molecules were brought to earth on comets. These could have then become more complex organic molecules, and eventually simple life forms
Why can’t the theories for how life started be supported or disproved?
Lack of valid and reliable evidence
Why is there a lack of evidence for theories for how life started? (2)
1) There’s a lack of evidence because scientists believe many early organisms were soft bodied and soft tissue tends to decay away completely. So the fossil record is incomplete
2) Fossils that formed millions of years ago may have been destroyed by geological activity
What causes extinction?
Extinction happens if you can’t evolve fast enough
List the reasons why extinction happens: (6)
1) The environment changes too quickly
2) A new predator kills them all
3) A new diseases kills them all
4) They can’t compete with another (new) species for food
5) A catastrophic event happens that kills them all
6) A new species develops (speciation)
