Absolute Time Flashcards
Define Zircons, why are they relevant
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.
Define Radioactive Decay
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.
Define Alpha Decay
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.
Define Beta Decay
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
explain the decay of Uranium 238 into lead 206
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
Define half life
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.
Define parent isotope
A radioactive atom that can and will decay.
Where is the most common place zircons are found
Volcanoes
Define Electron Capture
A type of radioactive decay where an electron combines with a proton, making a neutron.
Define the Auger Process
another electron is released and changes the atom into anion. The atomic number is reduced by 1 and mass number remains the same.
What are the two possible effects of electron capture after an electron becomes a neutron.
- an electron jumps in to fill the spot of the departed electron and emits an X-ray,
- The Auger process
what are the two key assumptions or principles behind radioactive age dating
- First the crystals formed at the same time as teh rock (crystallization of magma)
- The mineral crystals remain a closed system - nothing gets in or out (this method is better for determining time.
What kind of volcanic ash is more likely to have zircons
Felsic pyroclastic activity. The distribution is also notable as wind and water can carry these minerals farther.
Define the use of mass spectrometry
A device that can determine the amounts of different isotopes in a substance.
explain the process of dating when using a TIMS machine.
a
define daughter product
The atom that is made after a radioactive decay
why is U-pb important in deep time calculation
A
What is the difference between dating an igneous rock like Granite and a metamorphic rock like Gneiss, and why does it matter.
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.
zones on zircon grains
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.
Carbon 14 dating, explain the process, remeber the 60k time short half life
whole system has very short half life,
Define Absolute Dating
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.
Define Radiocarbon dating
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.
