12-1) discovering earth's history Flashcards
what is uniformitarianism?
the idea that the physical, chemical, and biological laws that operate today also operated in the past
what is relative dating?
determines the order of events and the relative age of rocks by examining the position of rocks in a sequence; top layer is younger but no exact age
what is absolute dating?
determines the age, in years, of an object
what is the law of superposition?
in undistribution layers, the oldest rocks are on the bottom and the rocks become progressively younger toward the top
what is the principle of original horizontality?
sediments are often deposited in horizontal layers to form sedimentary rocks, first and oldest layer on the bottom, layers form on top of previous one
what is the principle of cross-cutting relationships?
a fault or intrusion must be younger than the layers it cuts through, if there’s a fault running through, layers had to be there first before the fault could form in them
what is extrusion?
when lava flows on the surface and then hardens
what is intrusion?
when magma squeezes into spaces in the rock then cools into igneous rock
what is an unconformity?
when a surface represented a break in the rock record, long period which deposition stopped, erosion removed previously formed rocks and deposition resumed;
helps identify intervals of time
what are the types of unconformities?
angular, disconformity, and nonconformity
what is an angular unconformity?
sedimentary rocks are deposited originally as horizontal layers, tectonic forces uplift the layers exposing it to erosion and weathering, jagged junction
what is a disconformity?
when one layer of sedimentary rock layers look eroded, layers eroded above water and top layers are eroded away, new layers deposited on the buried erosional surface, erosional surface is buried below other layers, very jagged
what is a nonconformity?
erosional surface that separates older metamorphic or igneous rocks from younger sedimentary rocks
what are inclusions?
pieces of rock unit that are contained within another rock unit; Rock unit with inclusions is younger
what is correlation?
match rock layers at different locations that formed at the same time and formed by the same process; fossils help
