Lecture 9 - Carbon Isotopes

Question 1

fractionation

Answer 1

any process changing the ratio of isotopes
happens during photosynthesis, absorption into animal tissue, and pedogenesis (soil formation)

Question 2

photosynthesis

C4 vs C3

Answer 2

C4 = grasses, uptakes more C13 during photosynthesis
C3 = trees/shrubs

• c3 and c4 fractionate carbon in different ways
• grasses more able to absorb heavy carbon from environment (more c13 heavy)

Question 3

dental enamel

formation of dental enamel

Answer 3

• secreted by ameloblast cells
• gradually mineralized with carbonated hydroxypatite
• once crown is formed, ameloblasts die & formation is finished
• teeth form crown to root

Question 4

dental enamel

carbon entombment in teeth

Answer 4

• entombed when teeth are forming during juvenile period
• if diet changes during adulthood, will not be reflected in enamel record

Question 5

dental enamel

enamel sampling

Answer 5

• rotary tool with diamond bit allows for sampling
• can study carbon isotope rations of enamel powder
• since top enamel older than bottom, can be sampled to see diet over time
• enamel is a reservoir of carbon that is a time capsule

Question 6

carbon in soil

leaves in the fall

Answer 6

crushed up leaves eventually become absorbed by soil

Question 7

carbon in soil

soil

Answer 7

develop on rock surfaces as rock surfaces degrade and as organic material comes from above
- well formed soil has horizons (layers)
- takes 10s of Ks of years
- if eroded, washed away into ocean and can’t come back

Question 8

carbon in soil

carbonate formation during soil formation

Answer 8

carbonates form naturally as rock minerals react with water
- can build up in dry soils and preserve a record of the c13 profile of vegetation

Question 9

carbon in soil

paleosols

Answer 9

ancient soil buried in sedimentary record covered by other material (volcanic ash, landslides etc.)

preserves record of vegetation cover, can be millions of years old