B15 - Genetics + Evolution Flashcards
B15 - Describe how fossils are formed.
Animal dies and falls to the ground.
The flesh rots, and the skeleton gets covered in sand, soil or clay before it gets damaged.
The skeleton mineralises over millions of years.
The fossil emerges as the rocks move and erosion takes place.
B15 - Evaluating the use of fossils
The fossil record helps scientists understand how much organisms have changed since life developed on earth.
Pros:
Organisms with comprehensive fossil records show clear evidence of change over time.
Cons:
Understanding is often limited.
Only small pieces of skeleton/shell have been found.
Not all animals have changed. Sharks have remained relatively unchanged in their 300 million year existence.
Much of the fossil record is incomplete.
B15 - Explain why the fossil record is incomplete.
Early forms of life were soft bodied. They were destroyed by geological activity.
Organisms that died did not fossilize as the conditions were not right.
Many fossils are still yet to be found.
B15 - Extinction hypotheses
Extinctions can be caused by:
New predators, diseases or competitors
Volcanic eruptions
Tsunamis
Asteroid impacts
Earthquakes
Rises in temperature
B15 - Explain what is meant by a mass extinction
When a large proportion of the planets species are lost
Happens over a relatively short period of time
B15 - Describe theories used to explain mass extinctions
The most recent mass extinction event was when the dinosaurs became extinct 65 million years ago.
Scientists agreed that around this point in time, a giant asteroid collided with the earth in Chicxulub, Mexico.
Evidence:
There is a huge crater (180km in diameter) there.
A layer of rock formed from crater debris in countries across the world.
The further away you move from the crater, the thinner the layer of cater debris in the rock.
Iridium present deep below the crater - a mineral formed when a rock is hit with a massive force.
B15 - Describe the classification system developed by carl Linnaeus.
Kingdom
Phylum
Class
Order
Family
Genus
Species
B15 - Describe the three domain system of classification
Organisms on earth are split into 3 domains.
Bacteria - prokaryotic cells without a clear nuclear membrane. Some are pathogenic
Archaea - single celled organisms similar to bacteria. They lack cell organelles.
Eukarya - organisms that have true membrane bound organelles. Organisms in this domain include protists, fungi, plants and animals.
