Old and new species Flashcards
The earth is believed to be how many years old?
How many years ago did life begin?
4.5 billion years old
Life began 3.5 million years ago
How can we date when different organisms existed?
We can date rocks. Fossils are found in rocks so we can date when different organisms existed.
Explain the four main ways in which fossils may be formed?
1) From the hard parts of animals which do not decay easily, such as: bones, teeth, shells and claws.
2) From parts of organisms that have not decayed because some of the conditions for decay are absent, e.g. fossils of mammals preserved in ice.
3) When parts of organisms are replaced by other materials, such as minerals as they decay.
4) As preserved traces of organisms, e.g. footprints, burrows and rootlet traces.
Explain the three main reasons why fossils are rare.
1) Most organisms that died did not leave a fossil because the exact conditions for fossil formation were not present.
2) Many early life forms had soft bodies so few traces were left behind.
3) Traces which were left are likely to have been destroyed by geological activity such as earthquakes.
In what two ways do scientists debate life was formed on earth?
Either
1) Due the conditions on earth
OR
2) Simple life forms arrived from other planets.
What does extinction mean?
Extinction means a species that once existed has completely died out.
Give six factors which may cause extinction.
1) A new disease may kill all members of a species.
2) Changes in environment over geological time.
3) A new predator may evolve or be introduced to an area which effectively kills and eats all of a species.
4) A new competitor may evolve or be introduced to an area, the original species may be left with too little to eat.
5) A single catastrophic event may occur which destroys the habitat, e.g. a massive volcanic eruption.
6) Natural changes in species occur over time.
How can climate change affect a species?
Climate change may make it too cold/hot, or wet/dry for a species and reduce its food supply.
Give two different ideas about how dinosaurs became extinct.
1) The collision of a huge asteroid caused huge fire, earthquakes, landslides and tsunamis. The dust which rose masked the sun causing darkness and lower temperatures. Plants were unable to grow.
2) The extinction was a slower process due to sea ice melting and causing sea temperatures to fall by about 9ºC, therefore there was less plankton - less food available.
Give three reasons why geographical isolation may occur?
1) If an island separates from the mainland.
2) If a new river separates two areas.
3) Mountain ranges and old craters can separate two species.
Explain the process of speciation. (5)
At what point has speciation occurred? (Part 5)
1) Two populations of the same species can become separated as in geographical isolation.
2) Each population has a wide range of alleles that control their characteristics, their is genetic variation.
3) Natural selection will occur in each population, the alleles that control the characteristics which help the organism to survive are selected, the organisms with these alleles survive and breed.
4) If they environment, competitors, food supply and predators for each population is different, they will evolve differently.
5) Speciation has occurred when the two population can no longer successfully interbreed.
