EARTH SCIENCE 2ND QUARTER
DATING Radiometric dating calculates an age in years
Archaeologists have two main ways to tell the for geologic materials by measuring the presence
age of sites and artifacts. of a short-life radioactive element, e.g., carbon-
RELATIVE DATING 14, or a long-life radioactive element plus its
Relative dating uses rocks to determine past decay product, e.g., potassium-14/argon-40.
events' succession, indicating the age of a rock RADIOCARBON DATING
layer but not the exact duration. It applies A method that provides objective age estimates
stratigraphy laws to determine rock age. for carbon-based materials that originated from
TYPES OF RELATIVE DATING living organisms.
STRATIGRAPHY CARBON-14 DATING
Stratigraphy is the scientific study of rock A dating technique that utilizes carbon-14 to tell
layers (strata) and their arrangement in the age of an organic material for about 50,000
chronological order. years.
It examines the structure and order of layers, or CARBON-14
strata, as well as the formation, makeup, and A radioactive and unstable isotope of a carbon.
distribution of these geological layers. ISOTOPES
BIOSTRATIGRAPHY Atoms of the same element with differing
numbers of neutrons
Biostratigraphy - In this technique, the faunal
RADIOISOTOPES
deposits such as fossils of dead animals are used
Radioisotopes are radioactive isotopes of an
to establish a strategy for dating. It is an
element. They can also be defined as atoms that
extended version of the stratigraphy.
contain an unstable combination of neutrons
It is a specific branch of stratigraphy where it
and protons, or excess energy in their nucleus.
uses fossils found in the strata to serve as
RADIOACTIVE DECAY
biological markers and gives a precise estimate
Radioactive decay is the emission of energy in
of the rock’s unit age.
the form of ionizing radiation.
CROSS DATING
Cross dating is a method of using fossils to
determine the relative age of a rock. The more
basic the organism the older the rock is. This
practice supports the theory of evolution which
states that simple life forms gradually evolve
over time to form more complex ones. If
undisturbed, layers of sedimentary rocks help to HALF LIFE
determine the relative age of rock: the oldest The time taken for the radioactivity of a
being at the base and the newest on top. specified isotope to fall to half its original
It is the most basic principle of value.
dendrochronology. Cross dating is a technique
that ensures each individual tree ring is
assigned its exact year.
ABSOLUTE DATING
Absolute dating methods measure the physical POTASSIUM-ARGON DATING
properties of an object itself and use these Method of determining the time of origin of
measurements to calculate its age. rocks by measuring the ratio of radioactive
TYPES OF ABSOLUTE DATING argon to radioactive potassium in the rock.
RADIOMETRIC DATING URANIUM SERIES DATING
Radiometric dating the ratio of a parent and Uranium-series dating is a broad term covering
daughter isotopes in a sample can be measured several geological dating schemes based on the
measurement of the natural radioactivity of
and used to determine their age.
uranium isotopes.
EARTH SCIENCE 2ND QUARTER
THERMOLUMINESCENCE This principle states that a layer of sedimentary
Thermoluminescence - Igneous rocks are rock or sediment extends laterally from end to
formed by hot magma that has cooled over time. end.
Thermoluminescence- emission of light from Any breaks are due to erosion or deposition
some minerals and certain other crystalline after deposition.
materials.
STRATIGRAPHY
The term stratigraphy refers to the branch of
geology that studies stratified or layered rocks
in terms of time and space.
Stratum (plural strata) is the term used to
LAW OF SUPERPOSITION
describe rocks that form layers or beds.
The law of superposition states that in an
STRATIFICATION
undisturbed sequence of sedimentary rocks, beds
Stratification - the layering that occurs in
on top are younger than the beds found below,
most sedimentary rocks.
and each layer is younger than the one beneath it.
Each stratum contains a certain rock type and
may also enclose fossils. Common rock types
include sandstones, mudstones, and
conglomerates.
LAMINATION
PRINCIPLE OF CROSS-CUTTING
Lamination - refers to the presence of thin,
RELATIONSHIP
parallel layers within sedimentary rocks.
Disrupted pattern is older than the cause of
BEDS
the disruption.
Beds - are thicker than one centimeter, a
It can be used in relative dating because when
distinct, identifiable layer of rock or
one geologic unit cuts across another, the
sediment, reflecting a unique depositional
cutting unit must be younger than the unit that
event.
was cut.
Bedding planes refer to the surface that
separates one stratum from the other. INDEX FOSSILS
PRINCIPLES OF STRATIGRAPHY Any animal or plant preserved in the rock record
Steno's laws of stratigraphy describe the of the Earth that is characteristic of a particular
span of geologic time or environment.
patterns in which rock layers are deposited.
A useful index fossil must be distinctive or
LAW OF ORIGINAL HORIZONTALITY
easily recognizable, abundant, and have a
The law of original horizontality states that
wide geographic distribution and a short
sediments are generally deposited horizontally.
range through time.
In areas where the depositional environment has
1. The fossilized organism must be easily
a slope, the sediments will follow the surface of
recognizable. It must be easy to ID and look
deposition.
unique.
2. The fossils have to be geographically
widespread or found over large areas so that we
can use them to match layers separated by huge
distances.
PRINCIPLE OF LATERAL CONTINUITY
EARTH SCIENCE 2ND QUARTER
3. The fossil must have lived for only a short time,
so that it appears in only horizontal layer of
sedimentary rocks.
Index fossils are useful for correlating rock
layers because they are distinctive,
widespread, and existed for a relatively short
time. By finding the same index fossil in
different rock layers, geologists can determine
that those layers are of similar age, aiding in
the relative dating of geological formations.
METAMORPHIC ROCKS
Metamorphic rocks form when rocks are
subjected to high heat, high pressure, hot
mineral-rich fluids or, more commonly, some
combination of these factors.
Conditions like these are found deep within the
Earth or where tectonic plates meet.
