Chapter 8 Dating methods

Question 1

Chronometric dating (absolute dating)

Answer 1

Makes age of events based on fixed time scale by using radioactive decay.
Includes potassium argon, carbon dating, thermoluminescence, and dendrochronology.

Question 2

Radioactive decay

Answer 2

Measure of rate radioactive isotopes degrate at half life. Best rock samples come from K40 Ar40 and Ar40 Ar39.

Question 3

Potassium argon (K40 Ar40)

Answer 3

K40 decays by half every 1.3 billion years, over time it turns into Ar40. To date a fossil use soil around it. Best material is volcanic ash.
Zinjanthropus was 1st hominid fossil to be dated by K40 Ar40, it’s 1.8 mya.

Question 4

Carbon dating (C14)

Answer 4

Can only date organic material (wood, bone, carbon items). Only good for samples between 1-50 kya.
Has radiometric half life of 5730 years, same amount of time for half to decay.

Question 5

Thermoluminescence (TL)

Answer 5

when refired good for ceramics, clay cooking hearths, burned flint tools, and hearthstones.
Clays have radioactive elements, when potter fires at 500ºC it releases trapped particles, as they escape they release TL, when reheated test for Thorium decay.

Question 6

Dendrochronology

Answer 6

Tells health of tree from climate change. Paleoecological reconstruction. Tree ring dating based on known samples. 1 ring is 1 growing season or 1 year.
Astronomer A E Douglass in 10th century extended seasonal to yearly tree growth.

Question 7

Relative dating

Answer 7

Orders events but doesn’t scale exact age between them. Dates object relative (older/younger) order to another. Based on position in fossil/archaeological record.
Includes stratigraphy, biostratigraphy, and index fossils.

Question 8

Stratigraphy

Answer 8

Law of superposition is collection of surface levels over time, strata (level) is 1 layer of soil/rock, and older on and younger on top. Problem is earthquakes and volcanoes cause older layers to move on top of younger layers.

Question 9

Biostratigraphy (faunal correlation)

Answer 9

Use fossils in each layer to compare. Dated from known sites. Fauna is animals and flora is plants. Multi component site in Brazil. In 1987 strata A and C date to 1-3 mya, new fossils in Strata B are 2 mya.

Question 10

Index fossils

Answer 10

Remains of known age used to estimate geological stratum age. Ex.: Dating fossils of T rex vs lizard.