Chapter 8 Part 2 Flashcards
Isotope
An element with a variable number of neutrons in the nucleus
During radioactive decay an unstable isotope (parent)
Ejects material from its nucleus to become a daughter isotope
Three types of radioactive decay
Alpha decay
Beta emission
electron capture
Alpha decay
The parent ejects an alpha particle, made of two protons and two neutrons, from the nucleus
Beta emission
The parent emits a beta particle from the nucleus
Electron capture
An electron collides with the nucleus, converting a proton into a neutron
Radioactivity
Nuclei spontaneously break apart
An unstable isotope is referred to as the
Parent
Most important result of discovery of radioactivity
It provides a reliable method of calculating the ages of rocks and minerals that contain particular radioactive isotopes
Radiometric dating
Procedure of calculating the ages of rocks and minerals containing radioactive isotopes
Why is radiometric dating reliable?
The rates of decay for many isotopes have been precisely measured and do not vary under the physical conditions that exist in Earth’s outer layers
Half-life
The time that it takes for half of a radioactive sample to decay to its final, stable daughter product
As the percentage of radioactive parent atoms ____, The proportion of stable daughter atoms ___.
Declines, rises
Rules for a radioactive dating
1- Number of parent and daughter isotopes only changes by radioactive decay (closed system)
2-the amount of daughter at beginning is either zero or can be determined
3-The decay rate (half-life) has not changed over time
4-No errors in collection or analysis
Date=
Number of half-livesXrate
What can be dated?
Igneous (lava, ashes, intrusive)
Metamorphic (especially high-grade)
Since you can’t date sedimentary rocks, geologists do what?
Make brackets using surrounding rocks
The Carbon 14 system
- Carbon-14 is formed in the atmosphere all the time.
- A neutron collides with a nitrogen atom forming carbon-14
Carbon-14 will convert back to nitrogen via
Beta emissiom
Carbon-14 combines with oxygen to form
Carbon dioxide 14
Plants take in carbon dioxide 14 and make
Leaves, sugar, fruits and flowers which gets eaten by animals, protists and fungi
One carbon-14:
1 trillion Carbon 12
Carbon-14 in is _____ with Carbon-14 out
Balanced
What happens to carbon-14 when you die?
No more carbon-14 in
Carbon-14 half-life equals
5,730 years
an archaeologist uses the changing ratio of carbon-14 to Carbon 12 to
Date the sample
Carbon-14 can you be used today for anything that was
Biological
Biological
Wood, paper, bone, shells, cloth
For creationists, carbon-14 dating on fossils have been determined for
Oil, coal, natural gas, fossil shells and bones, petrified wood, diamonds
Carbon-14 dating can be used for
Dating events from the historical past as well as those from very recent geologic history
Where is carbon-14 produced?
In the upper atmosphere as a consequence of cosmic ray bombardment
Geologic timescale
The division of geologic history into units of varying magnitude
Eons represent the
Greatest expanses of time
Phanerozoic
Visible life
Eons are divided into
Eras
Three eras of Phanerozoic are
Paleozoic, Mesozoic, Cenozoic
Eras are divided into
Periods
Periods are divided into
Epochs
Precambrian
Informal name for the eons that came before the current Phanerozoic eon
The primary problem in assigning numerical dates is the fact that
Not all rocks can be dated by radiometric methods
