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proxy data a natural source used to infer
polar molecule a molecule with a dipole, principle of cross-cutting relationships a /207/es/MHDQ243/tiL12214_disk1of1/0073512214/tiL12214_pagefile s
with a negative side and a positive side frame of reference based on the under- temperature change, rainfall, or some other
Polaroid a film that transmits only polarized standing that any geologic feature that cuts climate condition of the past
light across or is intruded into a rock mass must Pseudoscience uses the appearance or lan-
polyatomic ion an ion made up of many be younger than the rock mass guage of science to mislead people into
atoms principle of faunal succession a frame thinking that something has scientific va-
polymers huge, chainlike molecules made of of reference based on the understand- lidity when it does not
hundreds or thousands of smaller repeat- ing that life-forms have changed through psychrometer a two-thermometer device
ing molecular units called monomers time as old life-forms disappear from the used to measure the relative humidity
polysaccharides polymers consisting of mono- fossil record and new ones appear, but Ptolemaic system geocentric model of the
saccharide units joined together in straight the same form is never exactly duplicated structure of the solar system that uses epi-
or branched chains; starches, glycogen, or independently at two different times in cycles to explain retrograde motion
cellulose history pulsars the source of regular, equally spaced
pond a small body of standing water, smaller principle of original horizontality a frame pulsating radio signals believed to be the
than a lake of reference based on the understanding result of the magnetic field of a rotating
porosity the ratio of pore space to the total that on a large scale, sediments are depos- neutron star
volume of a rock or soil sample, expressed ited in flat-lying layers, so any layers of pure substance material that is the same
as a percentage; freely admitting the pas- sedimentary rocks that are not horizontal throughout and has a fixed definite com-
sage of fluids through pores or small spaces have been subjected to forces that have position
between parts of the rock or soil deformed Earth’s surface pure tone a sound made by very regular in-
positive electric charge one of the two types principle of superposition a frame of refer- tensities and very regular frequencies from
of electric charge; repels other positive ence based on the understanding that an regular repeating vibrations
charges and attracts negative charges undisturbed sequence of horizontal rock P-wave a pressure, or compressional, wave
positive ion an atom or particle that has a layers is arranged in chronological order in which a disturbance vibrates materials
net positive charge due to an electron or with the oldest layers at the bottom, with back and forth in the same direction as the
electrons being torn away each consecutive layer younger than the direction of wave movement
potential energy energy due to position; one below it P-wave shadow zone a region on Earth
energy associated with changes in posi- principle of uniformity a frame of reference between 103° and 142° of arc from an
tion (e.g., gravitational potential energy) of slow, uniform changes in Earth’s history; earthquake where no P-waves are received;
or changes in shape (e.g., compressed or the processes changing rocks today are the believed to be explained by P-waves being
stretched spring) processes that changed them in the past, or refracted by the core
power the rate at which energy is transferred “the present is the key to the past”
or the rate at which work is performed; de- proof a measure of ethanol concentration of Q
15
fined as work per unit of time an alcoholic beverage; proof is double the quad 1 quadrillion Btu (10 Btu); used to
Prearchean the earliest of the geologic eons concentration by volume—for example, describe very large amounts of energy
before life 50 percent by volume is 100 proof quanta fixed amounts; usually referring to
Precambrian one of four geologic eras; the properties qualities or attributes that, taken fixed amounts of energy absorbed or emit-
time before the time of ancient life, mean- together, are usually unique to an object— ted by matter (quanta is plural, and quan-
ing the rocks for this time period contain for example, color, texture, and size tum is singular)
very few fossils proportionality constant a constant applied quantities measured properties; they in-
precession the slow wobble of the axis of to a proportionality statement that trans- clude the numerical value of the measure-
Earth similar to the wobble of a spinning top forms the statement into an equation ment and the unit used in the measurement
precipitation water that falls to the surface proteins macromolecular polymers made quantum mechanics a model of the atom
of Earth in the solid or liquid form of smaller molecules of amino acids, with based on the wave nature of subatomic par-
pressure defined as force per unit area—for molecular weight from about 6,000 to ticles, the mechanics of electron waves; also
2
example, pounds per square inch (lb/in ) 50 million; proteins are amino acid poly- called wave mechanics
primary coil part of a transformer; a coil of mers with roles in biological structures or quantum numbers numbers that describe
wire that is connected to a source of alter- functions; without such a function, they are energy states of an electron; in the Bohr
nating current known as polypeptides model of the atom, the orbit quantum
primary loop part of the energy-converting Proterozoic the geologic eon before the numbers could be any whole number 1, 2,
system of a nuclear power plant; the closed Phanerozoic, meaning “beginning life” 3, and so on out from the nucleus; in the
pipe system that carries heated water from protogalaxy a collection of gas, dust, and quantum mechanics model of the atom,
the nuclear reactor to a steam generator young stars in the process of forming a galaxy four quantum numbers are used to de-
prime meridian the referent meridian (0°) proton the subatomic particle that has the scribe the energy state of an electron wave
that passes through the Greenwich Obser- smallest possible positive charge, usually
vatory in England found in the nucleus of an atom R
principal quantum number from the quan- protoplanet nebular model a model of the rad a measure of radiation received by a
tum mechanics model of the atom, one of four formation of the solar system that states material (radiation absorbed dose)
descriptions of the energy state of an electron that the planets formed from gas and dust radiant energy the form of energy that can
wave; this quantum number describes the left over from the formation of the Sun travel through space—for example, visible
main energy level of an electron in terms of protostar an accumulation of gases that will light and other parts of the electromagnetic
its most probable distance from the nucleus become a star spectrum

Glossary G-12