deep time (wk4)

DEEP TIME

the immense span of geologic time

RELATIVE AGE

tells the age of a feature in relation to another feature (e.g. one rock layer is older than another)

NUMERICAL AGE

gives the specific ages in years (e.g. rock is 50 ma)

Ka

thousands years

Ma

millions years

Ga

billions years

UNIFORMITARIANISM

Physical processes observed today were the same in the past; 'PRESENT IS KEY TO THE PAST'

PRINCIPLE OF ORIGINAL HORIZONTALITY

Gravity causes sediments to accumulate in horizontal sheets; sediment on steep slope will slide downslope before lithification

PRINCIPLE OF SUPERPOSITION

Sedimentary rock layers = each layer is younger than one below; bottom = oldest, top = youngest

PRINCIPLE OF LATERAL CONTINUITY

Sedimentary layers spread out in all directions when first formed; rock layer on either side of canyon used to be connected before river eroded through it

CROSS-CUTTING RELATIONS

Intrusions / faults / erosion surfaces cut across older features e.g. layers of sedimentary rock; sedimentary rock = older

PRINCIPLE OF INCLUSIONS

Inclusion = fragment of one rock incorporated in another; must be older than rock that contains it

Xenolith

Helps distinguish sills from lava

PRINCIPLE OF CHILLED MARGINS / BAKED PRODUCTS

During igneous intrusion formation, hot magma injects into cooler rock; rock that is baked = older than intrusion

UNCONFORMITIES

gap in the rock record; represents missing time in Earth's history (layers that should be present are not)

STRATIGRAPHIC BREAKS

also referred to as stratigraphic breaks; represents missing time in Earth's history

TIME INTERVALS

caused by lack of deposition / erosion

Hutton's observation

outcrop had strata consisting of red sandstone + conglomerate that rested on different sequences of gray sandstone + shale

VERTICAL DIP

Beds of gray sandstone + shale = vertical dip

DIP OF 15°

Beds of red sandstone + conglomerate = dip of only 15°

EROSION

the process that cut off the gray sandstone + shale long before red sandstone + conglomerate beds had been deposited

ANGULAR UNCONFORMITY

Strata below was tilted/folded before unconformity developed making unconformity younger.

NONCONFORMITY

Sedimentary rocks overlie older intrusive igneous rocks / metamorphic rocks.

DISCONFORMITY

Sedimentary beds below water undergo exposure (sea levels drop), erosion and new when sea levels rise, new sedimentary layers deposited.

Formation of Angular Unconformity

1. Sedimentary layers due to tectonic forces either tilt, fold, deform or uplift. 2. Erosion wears down tilted rock creating flat surface. 3. New horizontal layers are deposited on top (often due to sea level rises).

Formation of Nonconformity

1. Pluton intrudes. 2. Erosion cuts down into crystalline rock. 3. New sedimentary layers build up on top of older erosion surface.

Formation of Disconformity

1. Layers of sediment build up below sea. 2. Sea levels drop, surface of sediment erodes. 3. Sea level rises, new sedimentary layers build up.

STRATIGRAPHIC FORMATIONS

A stratigraphic formation = a distinct layer of rock that can be identified + tracked over a large area.

Geologic Column

Composite stratigraphic column that represents earth's history, separated into segments which each represent a specific time intervals.

THE CAMBRIAN EXPLOSION

541 ma, shown through fossils, skeletons, shells, dramatic increase in diversity + complexity, animals that exist today first appeared in fossil record from this period.

CRETACEOUS-PALEOGENE (K-PG) EXTINCTION

66 ma, asteroid struck + volcanic activity = mass extinction, end of mesozoic era, beginning of cenozoic era, dinosaurs extinct, 75% species extinct.

NEOGENE / QUATERNARY PERIOD

Humans appeared.

DETERMINING NUMERICAL AGE

Radioactive elements decay at a measurable rate, its atoms transform into different atoms of another element.

RADIOISOTOPIC DATING

Uses decay rates to calculate rock ages.

GEOCHRONOLOGY

Study of determining rock ages.

Isotopes

Versions of atom with extra neutrons in them.

Half-life

The amount of time it takes for one half of the isotope to decay.

Carbon dating

Dating using carbon 14, which has a half life of 5700 years and most of it will be gone in about 50,000 years.

Uranium 238

An isotope that decays very slowly with a half-life of 4.5 billion years.

Parent Isotope

The unstable radioactive element used in dating.

Daughter Isotope

The stable isotope that results from the breakdown of the parent isotope.

Decaying

The process of a parent isotope changing to become a daughter isotope.

Half-Life

The time it takes for half the parent isotopes to change into daughter isotopes.

Radiometric Dating

The process of determining the age of rocks or elements by measuring the decay of isotopes.

Counting Parents and Daughters

The method of measuring how many parent and daughter isotopes are left in the rock.

Young Rock

A rock that has many parent isotopes and few daughter isotopes, indicating not much time has passed.

Old Rock

A rock that has many daughter isotopes, indicating most of the parent isotopes have decayed.

Stable Isotope

An isotope that does not undergo radioactive decay.

Unstable Isotope

An isotope that has too many neutrons and decays over time.

Transformation

The process by which a parent isotope decays into a daughter isotope.

Decay Rate

The speed at which a parent isotope transforms into a daughter isotope.

Isotope

Atoms of the same element that have different numbers of neutrons.

Scientific Measurement

The process of quantifying the number of parent and daughter isotopes in a rock.

Age Calculation

The determination of how long the rock has been around using half-life and isotope counts.

Radioactive Decay

The process by which an unstable isotope loses energy by emitting radiation.

Element Formation

The initial state of a rock when it has a lot of parent isotopes.

Half of Parent Atoms

Refers to half of the parent isotopes that have decayed into daughter isotopes over one half-life.

Stable Form

The more stable state that a parent isotope transforms into after decay.

Decay Process

The gradual change of a parent isotope into a daughter isotope over time.

Isotope Count

The number of parent and daughter isotopes present in a sample.

Time Measurement

The estimation of the duration since the rock was formed based on isotope data.

Neutron Count

The number of neutrons in an isotope that can affect its stability.

Stable Parent Isotope

A parent isotope that has decayed completely into daughter isotopes.