Absolute Time

Question 1

Define Zircons, why are they relevant

Answer 1

Zircons can survive processes like erosion, transport and metamorphism, so they preserve a record of past geological processes. They are one of the key minerals used by geologists to determine the age of rocks.

Question 2

Define Radioactive Decay

Answer 2

There are a number of elements that are not stable, this includes all elements with an atomic number greater than 83, and many isotopes that have a few too many neutrons. This leads to the nucleus becomes unstable and starts to decay into other elements.

Question 3

Define Alpha Decay

Answer 3

Alpha decay is a nuclear decay process where an unstable nucleus changes to another element by shooting out a particle composed of two protons and two neutrons. This ejected particle is known as an alpha particle and is simply a helium nucleus.

Question 4

Define Beta Decay

Answer 4

is when a neutron in its nucleus splits into an electron and a proton. The electron is emitted from the nucleus as a beta ray. The new proton increases the element’s atomic number by one, forming a new element with the same atomic mass as the parent isotope

Question 5

explain the decay of Uranium 238 into lead 206

Answer 5

a neutron from the nucleus splits into an electron and a proton; the electron is emitted as a beta ray and the proton gives the new element an atomic number of 91. Slide 10

Question 6

Define half life

Answer 6

The time for half of the parent to decay to an equal amount of daughter is called the “half life
In other words, the half-life of an isotope is the amount of time it takes for half of a group of unstable isotopes to decay to a stable isotope.

Question 7

Define parent isotope

Answer 7

A radioactive atom that can and will decay.

Question 8

Where is the most common place zircons are found

Answer 8

Volcanoes

Question 9

Define Electron Capture

Answer 9

A type of radioactive decay where an electron combines with a proton, making a neutron.

Question 10

Define the Auger Process

Answer 10

another electron is released and changes the atom into anion. The atomic number is reduced by 1 and mass number remains the same.

Question 11

What are the two possible effects of electron capture after an electron becomes a neutron.

Answer 11

1. an electron jumps in to fill the spot of the departed electron and emits an X-ray,
2. The Auger process

Question 12

what are the two key assumptions or principles behind radioactive age dating

Answer 12

1. First the crystals formed at the same time as teh rock (crystallization of magma)
2. The mineral crystals remain a closed system - nothing gets in or out (this method is better for determining time.

Question 13

What kind of volcanic ash is more likely to have zircons

Answer 13

Felsic pyroclastic activity. The distribution is also notable as wind and water can carry these minerals farther.

Question 14

Define the use of mass spectrometry

Answer 14

A device that can determine the amounts of different isotopes in a substance.

Question 15

explain the process of dating when using a TIMS machine.

Answer 15

a

Question 16

define daughter product

Answer 16

The atom that is made after a radioactive decay

Question 17

why is U-pb important in deep time calculation

Answer 17

A

Question 18

What is the difference between dating an igneous rock like Granite and a metamorphic rock like Gneiss, and why does it matter.

Answer 18

Dating granite, will give you the crystallization age of the rock while dating Gneiss will might reflect the timing of metamorphism. This matters as the metamorphic events may not represent the original crystallization.

Question 19

zones on zircon grains

Answer 19

Zircon is resistant to weathering which makes it useful for dating geological events in ancient rocks. During metamorphic events, zircon crystals may form multiple crystal layers, with each layer recording the isotopic age of an event, thus tracing the progress of the several metamorphic events.

Question 20

Carbon 14 dating, explain the process, remeber the 60k time short half life

Answer 20

whole system has very short half life,

Question 21

Define Absolute Dating

Answer 21

Using radioisotopic dating, scientists can assign specific time units, in this case years to mineral grains within a rock. These numerical values are not dependent on comparisons with other rocks such as with relative dating.

Question 22

Define Radiocarbon dating

Answer 22

using the unstable isotope carbon -14 and the stable isotope carbon -12 in organisms, when an organism dies carbon -14 starts decaying through beta decay back into Nitrogen-14.