Flashcards in Fossils Deck (24)
What is a fossil
Any preserved trace left by an rganisms that lived in the past
What are types of fossil
How are fossils formed
Formed when hard body parts or organisms such as bone or teeth are buried by drifting sand, deposited by rivers, volcanic ash
Requirements for fossil formation
1. Quick burial
2. Presence of hard body parts
3. Absence of decay microorganisms
4. Long period of being left undisturbed
Where are fossils often found?
1. Near lakes and rivers due to build up of sediment when flooding occurs
2. In caves because limestone may be deposited around dead organisms or the roof of the cave may collapse
3. Or found by chance or excavation of a site
What are artefacts
Objects that have been deliberately made by humans
Examples of artefacts
How does the fossil record provide evidence for evolution
It provides evidence of which organisms lived on earth in the past and establishes links between species to determine commmon acenstry
What are the two types of dating
What is absolute dating?
Finding the actual date of a specimen
What is relative dating?
Tells us if the sample is older or younger than the other
What is potassium argon dating
It is dating volcanic rock next to the fossil not the fossil itself
What is the P-A dating based on?
Based on the decay of radioactive potassium 40 to form calcium and argon
What is P-A dating half-life?
Potassium has a half-life of 1.25-1.3B years so, over a period of 1.25B years, half the original potassium -40 would have decayed
How can P-A age fossils?
The ratio of potassium 40 to argon 40 determines the age in a rock sample, the ratio of argon compared to potassium the older it is
What is the limitations of P-A
1. Not all rocks are suitable because not all rocks are volcanic
2. Can only date a rock sample, not the fossil itself
3. Only date samples past 200 000 years
4. Must be suitable rock of the same age as the fossil
What is radio carbon dating based on?
Based on the decay of radioactive isotope of carbon -14 to nitrogen
What is the half-life of R-C dating?
Half life is 5730 years, so over a period of 5730 years there will be half the original carbon 14 amount
How can R-C dating help to date fossils?
The ratio of carbon -14 to carbon 12 can help to determine the age of the fossil
What is the limitations of R-C dating?
1. Required 3 grams of organic material
2. After 70 000 years the quantity of carbon -14 is too small to be used, can only date back than 60,000 years
What is stratigraphy
The study of layers
What are the principles of stratigraphy
1. Principle of rock strata
2. Principle of correlation of rock strata
What is the principle fo rock strata
Assumes layers of the rock, the layers at the top are the younger than the below
Distortions in the earth's crust do occur and the sequence of rock layers can be different