Geologic Time Flashcards
means that the forces and processes that we observe today have been at work for a very long time. This means that the forces that keep on changing Earth have been working for very long periods of time since the beginning of Earth’s history.
uniformitarianism
a Scottish geologist, proposed the principle of uniformitarianism
James Hutton
james hutton quote
“the present is the key to the past”
relative dating is determined by
stratified rocks
fossils
absolute dating is measured by
radioactive dating
fossils
A method of showing the sequence of events; that is, which happened first, next, and so on. For example, the rocks beneath a volcano were formed much ahead of the volcano, which means that a volcano is younger than the rocks beneath it.
relative dating
science that deals with the characteristics of layered rocks and how these rocks are used to trace Earth’s history
stratigraphy
formed over time by wind, rain and glacial formations. These rocks may be formed by folding and tilting, faulting, and volcanic intrusions.
stratified rocks
studied the relative positions of sediments in sedimentary rocks.
nicolas steno
states that in an undeform sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below it.
law of superposition
states that sediments are deposited in flat layers. Thus, if the rock still maintains its horizontal layers, it means that it is not yet disturbed and still has its original horizontality.
Principle of Original Horizontality
states that when a fault cuts through rock layers, or when magma intrudes other rocks and crystallizes, we can assume that the fault or intrusion is younger than the rocks affected.
Principle of Cross-Cutting Relationships
Inclusions are rocks contained within other rocks. Rocks containing inclusions are younger than the inclusions they contain.
inclusions principle
rock layers that formed without interruption.
conformable
a layer of rock that was deformed or eroded before another layer was deposited, resulting in rock layers that are mismatched.
uncomformity
younger sediments rest upon the eroded surface of tilted or folded older rocks.
angular uncomformity
contact between younger and older beds is marked by a visible, irregular or uneven erosional surface.
disconformity
beds above and below the unconformity are parallel and no erosional surface is evident; but can be recognized based on the gap in the rock record.
paraconformity
develops between sedimentary rock and older igneous or metamorphic rock that has been exposed to erosion.
nonconformity
is establishing the equivalence of rocks of similar age in different areas.
correlation
a system of chronological dating that relates rock strata to time.
geologic time scale
is the science that deals with the study of fossils.
paleontology
are the remains or traces of prehistoric life. They are important components of sediment and sedimentary rocks.
fossil
Some remains of organisms—such as teeth, bones, and shells—may not have been altered, or may have changed hardly at all over time.
unaltered remains
The remains of an organism are likely to be changed over time.
altered remains
are the actual remains that did not change through time like teeth, bones, and shells of animals.
true form fossil
or fossils that turned into stone were formed when all or parts of organisms were replaced by minerals.
petrified fossil
preserve the form and shape of organisms. Molds are formed when organisms buried in sediments decay or dissolve. When minerals are deposited within the molds, casts can be formed.
molds and casts
result from a process undergone by leaves and delicate animal forms, through which they are covered with fine sediments.
carbonized fossil
is the hardened resin of ancient trees where insectsare preserved.
amber/preserved
states that the fossils of organisms succeed one another in a specific and well-established order, and that any geologic time or period can be recognized by the kind of fossil present.
Principle of Fossil Succession
The principle of fossil succession was formulated by
william smith
are fossils of organisms that lived only for a short period of time and are found in most places on the planet.
index fossil
A methods, sometimes called numerical dating, gives rocks an actual date or date range in number of years.
absolute dating
are atoms of the same element having the same number of protons but with different numbers of neutrons in their nuclei.
isotopes
the forces among the particles that makeup the nucleus are balanced.
stable
these forces are unbalanced; if the nucleus has an excess of either neutrons or protons.
unstable
is the spontaneous decay of certain unstable atomic nuclei.
radioactivity
is the amount of time necessary for one-half of the nuclei in a sample to decay to a stable isotope.
half life
is a type of radioactive disintegration in which some unstable atomic nuclei dissipate excess energy by spontaneously ejecting an alpha particle.
alpha emission
occurs when the ratio of neutrons to protons in the nucleus is too high. An excess neutron transforms into a proton and an electron. The proton stays in the nucleus and the electron is ejected energetically
beta emission
occurs when there are too many protons in the nucleus, and there isn’t enough energy to emit a positron.
electron capture
is the procedure of calculating the absolute ages of rocks and minerals that contain radioactive isotopes.
radiometric dating
is the method for determining age by comparing the amount of carbon-14 to the amount of carbon-12 in a sample.
radiocarbon dating
