Chapter 3 (part 1) Flashcards
Time and Geology
The science that deals with determining the ages of rocks is called ____
Geochronology
____ uses fundamental principles of geology (Steno’s Laws, Fossil Succession, etc.) to determine the relative ages of rocks (which rocks are older andwhich are younger).
Relative Dating
____ quantifies the date of the rock in years. This is done primarily by radiometric dating (or analysis of the breakdown of radioactive elements in the rocks over time).
Absolute Dating
____ Has been determined bit-by-bit over the years through relative dating, correlation, examiniation of fossils and radiometric dating
The Geologic Time Scale
____ are the largest division of geologic time.
Eons
The Precambrian covers ____ of geologic history.
87%
There are three ____ in the Phanerozoic Eon & are divided into geologic periods.
Eras
Eras are divided into ____
Periods
Periods can be subdivided into ____
Epochs
Epochs can be subdivided into ____
Ages
____ are the actual rocks formed or deposited during a specific time interval. They are sometimes called time-rock units.
Chronostratigraphic Units
The Archean and Proterozoic are together referred to as the ____ , meaning “before the Cambrian Period”.
Precambrian
The ____ is the smallest particle of matter that can exist as a chemical element.
Atom
If there is an unequal number of protons and electrons, the atom has a charge (positive or negative), and it is called an ____
Ion
The ____ of an atom = number of protons in the nucleus of that atom.
Atomic Number
The atomic number of uranium is ___
92
The ____ is the sum of the number of protons plus neutrons.
Mass Number
Uranium-235 has 92 protons and ____ neutrons.
143
The mass number may vary for an element, because of a differing number of ____
neutrons
Elements with various numbers of neutrons are called ____ of that element.
Isotopes
As ____ decays to lead, there are 13 intermediate radioactive daughter products formed (including radon, polonium, and other isotopes of uranium), along with and 8 alpha particles and 6 beta particles released.
Uranium-238
____ particles are large, easily stopped by papercharge = +2 mass = 4
Alpha
____ particles - penetrate hundreds of times farther than alpha particles, but easily stopped compared with neutrons and gamma rays.charge = -1 mass = negligible
Beta
____ are highly penetrating no charge mass = 1
Neutrons
____ are highly penetrating electromagnetic radiation which can penetrate concrete. Lead shield can be used. Photons (light). no charge no mass.
Gamma rays
high energy x-rays
Naturally-occurring radioactive materials break down into other materials at known rates.This is known as ____ decay.
Radioactive
Many radioactive elements can be used as geologic clocks because each radioactive element ____ at its own constant rate.
Decays
Geologists can estimate the length of time over which decay has been occurring by can be found by measuring the amount of radioactive parent element and the amount of stable ____
Daughter Elements
The quantities and masses of atoms and isotopes are measured using an instrument called a ____
Mass Spectrometer
The mass spectrometer came into use after ____
WWI (1918)
The mass spectrometer led to the discovery of more than ____ isotopes.
200
Radioactive decay occurs at a constant ____ or geometric rate.
Exponential
The rate of decay is proportional to the number of ____ atoms present.
Parent
Each radioactive isotope has its own unique ____
Half-Life
A half-life is the time it takes for half of the parent radioactive element to decay to a ____
Daughter Product
What rocks are best for age dating?
Igneous Rocks
(the dates they give tell when the magma cooled- when the magma cools and crystallized containing some radioactive elements that can be dated.)
The ages of sedimentary rocks and fossils are determined using ____
Both Relative & Absolute Dating
The ages of fossils in a sequence of sedimentary rocks can be determined using ____
Both Relative & Absolute Dating
Cosmic rays from the sun strike nitrogen-14 atoms in the atmosphere and cause them to turn into radioactive carbon-14, which combines with oxygen to form ____
Radioactive Carbon Dioxide
Living things are in equilibrium with the atmosphere, and the radioactive carbon dioxide is absorbed and used by____. The radioactive carbon dioxide gets into the food chain and the carbon cycle.
Plants
All living things contain a constant ratio of ____
Carbon-14 to Carbon-12.
1 in a trillion
What is the basis for Carbon-14 dating?
The Change In Carbon-14 to Carbon-12 Ratio
Carbon-14 dating can only be used on materials less than ____. Assuming that the rate of carbon-14 production has been constant.
70,000 years old
Charged particles from radioactive decay pass through mineral’s crystal lattice and leave trails of damage called ____
Fission Tracks
____ looks at the number of tracks per unit area is a function of age and uranium concentration.
Fission Track Dating
The oldest rocks that have been dated are ____. They date from the time of the origin of the solar system and the Earth, about 4.6 billion years old.
Meteorites
The oldest Moon rocks are from the ____, and may represent the original lunar crust.
Lunar Highlands
the ighter-colored areas on the moon
The oldest dates of Earth rocks are ____ detrital zircon grains in a sandstone in western Australia.
4.2 Billion Years Old
