Lecture 2 - the nature of the fossil record

Question 1

to become a useful fossil an organism must:

Answer 1

1 - die and avoid destruction by biological and physical processes
2 - be transported into an environment where it is incorporated into a sediment - then fossilised by taphonomy
3 - that sediment must then avoid destruction by diagenetic, metamorphic or erosive processes
4 - fossil must become exposed at the surface and discovered by someone who will study it

Question 2

why is the fossil record incomplete?

Answer 2

1 - sediment only accumulates over a very small area of the earth at any given time
2 - only a tiny fraction of the organisms that ever live will be fossilised
3 - most fossils will be destroyed with the rock that contains them
4 - only a tiny fraction of fossils ever formed will be collected and studied

Question 3

why is the fossil record biased?

Answer 3

1 - certain organisms/ parts of organisms are preferentially preserved
2 - certain environments preferentially preserve sediment and hence fossils
3 - older rocks are more likely to be destroyed
4 - collector bias e.g. from different parts of the world

Question 4

organisms that leave a fossil record are:

Answer 4

bacteria - sheath and structures built by bacteria
protists - those that form exo- and endoskeletons
plants - woody tissues (lignin), cuticles and spores preserve well
fungi - chitinous spores and hyphae preserve well
animals - those with recalcitrant exo- and endoskeletons

Question 5

oceanic crust covers what percentage of the planet?

Answer 5

70%

Question 6

why does most sediment occur on continental crust?

Answer 6

oceanic crust is constantly created / destroyed therefore sediment doesn’t build up

Question 7

what are large-scale bias’ related to the earth-system?

Answer 7

1. sea level changes - due to long term climate trends and continental configuration
2. continental configuration - more / less shelf
3. atmospheric composition - e.g. oxygen level

Question 8

how do we successfully interpret the fossil record?

Answer 8

• plot the spatial and temporal distribution of fossils therefore allowing us to work out the plate positions at that time

Question 9

when interpreting the fossil record we can also consider:

Answer 9

• ghost ranges - sharing of common ancestors

- probabilities of range extensions

Question 10

when interpreting the fossil record we can analyse

Answer 10

• volume of rock deposited per time slice

- exposed area of rock per time slice

Question 11

Dinosaur time span?

Answer 11

• first appeared in the Triassic period
• late Jurassic more familiar, larger dinosaurs evolve
• early late Cretaceous period, birds appear
• late Cretaceous period mass extinction