Time and Geology

Question 1

What two ways can Geologic Time be measured?

Answer 1

Through Relative Dating and Absolute Dating.

Question 2

What is Relative Dating?

Answer 2

Relative Dating is based on stratigraphy and gives the relative age of rocks.

Question 3

What is Absolute Dating?

Answer 3

Gives the age of rocks in years, determined by decay of radioactive elements.

Question 4

What is the accepted age of the Earth?

Answer 4

The absolute age of the Earth is accepted at 4.6 BY.

Question 5

What were some early methods used to estimate how old the Earth was?

Answer 5

Salts in the ocean, the accumulation of sediment, and the Earth’s temperature.

Question 6

How old was the world estimated to be due to salts in the ocean?

Answer 6

90 MY.

Question 7

How old was the world estimated to be due to the accumulation of sediment?

Answer 7

100 MY or less, this was flawed due to gaps in the stratigraphic record by unconformities that represent large breaks in accumulation. This method didn’t include metamorphosed sedimentary rocks.

Question 8

How old was the world estimated to be due to the Earth’s temperature?

Answer 8

Measured in Kelvin, 20-40 MY. This was flawed because of the heat coming from radioactive decay.

Question 9

Who discovered Radioactive Decay?

Answer 9

Becquerel (1895) saw that Uranium undergoes spontaneous decay. The atoms release subatomic particles and energy, and change to another element. The parent isotope decays into the daughter isotope.

Question 10

What are the three modes of decay?

Answer 10

1) Loss of Alpha Particle
2) Loss of Beta Particle
3) Capture of Beta Particle

Question 11

What is decay by mode of loss of alpha particle?

Answer 11

Convert parent into element that has nucleus containing two fewer protons.

Question 12

What is decay by mode of loss of beta particle?

Answer 12

Covert parent into element whose nucleus contains one more proton by losing an election.

Question 13

What is decay by mode of capture of beta particles?

Answer 13

Convert parent into element whose nucleus has one less proton.

Question 14

What is the principle of cross-cutting relationships?

Answer 14

(Lyell) The object that cuts through another object must be younger than the object it is cutting through.

Question 15

What is the principle of inclusions?

Answer 15

(Lyell) If inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them.

Question 16

Why can Radiometric Dating be used?

Answer 16

Because Radioactive isotopes decay at a constant geometric rate. After a certain amount of time, half of the parent present will survive and half will decay to the daughter.

Question 17

What is Half-Life?

Answer 17

Interval of time for half of parent isotope to decay.

Question 18

What are useful isotopes for Absolute Aging?

Answer 18

Uranium 238 and thorium 232 (zircon grains).
Uranium 238 and lead 206 (fission track dating).
Rubidium-Strontium.
Potassium-Argon, Argon-Argon.
Radiocarbon dating.

Question 19

What is Radiocarbon dating?

Answer 19

Using carbon that was produced in the upper atmosphere, with a half life of 5730 years. The maximum age for dating is 70,000 years and it is used for bone, teeth, and wood.

Question 20

What is Fission-Track Dating?

Answer 20

A measure of decay of uranium 238 by counting number of tracks formed by subatomic particles that fly apart upon decay.

Question 21

What are the best candidates for most radiometric dating?

Answer 21

Igneous, but not necessarily useful for sediments. The error in age estimate can be sizeable.

Question 22

What are usually more accurate than Radiometric dates?

Answer 22

Biostratigraphic correlations when fossils are present.