Geologic Time
What is Relative Geologic Time?
interpreting past geologic events in their order of occurence
What is latitude and what is longitude?
latitude- angle measured both northward and southward from the equator, which is assigned a value of zero
longitude- angle measured both westward and eastward from a meridian running through Greenwich, England (the prime meridian), which is assigned a value of zero
What are chemical elements?
the most fundamental substances into which matter can be subdivided by chemical means
What is an igneous rock?
rocks that have crystallized from molten rock
What is physical erosion?
the erosion of rocks largely by wind and water to produce solid particles such as clay, silt, sand, and pebbles-which can become cemented together to form detrital sedimentary rocks
What is Absolute Geologic Time?
solving for ages, in years, of past geologic events as recorded by 'geological clocks'
What is a fractional scale?
either a ratio or a representative fraction, designating the length of the line on the map equal to 1
What is a mineral?
a naturally formed, solid, chemical substance having (a) a specific composition and (b) a characteristic crystal structure
What is lava?
molten rock that spills out onto the ground
What is chemical weathering?
the alteration of rocks by water to produce chemical elements in solution and (commonly) residual clay
What is Geology?
the concept of practically limitless time and the belief the Earth's many landforms are products of present-day processes
What is a township?
a rectangular system of public land survey that has since been adopted by some 30 states
What is crystallography?
the study of crystal structures-deals with much of the same principles of geometry
What is a geothermal gradient?
the rate of downward increase in temperature
How are detrital sedimentary rocks classified?
according to the sizes of their grains
What is the Principle of Inclusions?
fragments of rock that become entombed in another rock are older than the rock in which they become entombed
What is a section?
one square mile (640 acres) in one area; delineated by section lines, and each bears its number in its center
What are silicate minerals?
a group within the chemical classification of minerals; igneous origin- they crystallize from molten rock
What is differentiation?
the segregation of elements that were present in the initial magma
What do organic limestones consist of?
fragments of sea shells cemented together
What is the Principle of Superposition?
when first accumulating, younger layers of rock overlie older layers of rock- like sand in an hourglass
What is True North?
the direction to Earth's north rotational pole
What is a streak?
more reliable than the color of a mineral is the color of its streak; powdered mineral; produced by rubbing the mineral on a streak plate
What is mineral composition?
the kinds and amounts of minerals present
What do coals consist of?
the organic carbon residue of plants that were buried with sediments and later compacted and distilled by the heat and pressure of burial