Science geologic time

absolute age

age of rock given as the number of years since the rock formed

Eon

A unit of geologic time equal to 1billion years

carbon dating

the determination of the age or date of organic matter from the relative proportions of the carbon isotopes carbon 12 and carbon 14 that it contains. The ratio between them changes as radioactive carbon 14 decays and it is not replaced by exchanged with the atmosphere

crosscutting relationships

a principle of geology that states that the geologic feature which cuts another is the younger of the two features. and is a relative dating technique in geology

Superposition

A principle explaining that in a section of undisturbed sedimentary rock the oldest layer of rock will be at bottom and the youngest layer will be at the top

Epoch

the smallest unit of geologic time, subdivision of a period

geologic timescale

a record of the geologic events and lifeforms in earths history

Ice cores

Ice cores are cylinders of ice drilled from ice sheets and glaciers. They are essentially frozen time capsules that allow scientists to reconstruct geologic history based on climate change.

Era

A fixed point in time from which a series of years is reckoned.

Index fossil

Any animal or plant preserved in the rock record of the any animal or plant preserved in the rock record of the earth that is characteristic of a particular span of geologic time.

Uniformitarianism

Earth’s geologic processes acted in the same manner and with essentially the same intensity in the past as they do in the present.

bending

when a rock layer bends over on itself so that one part of it covers another

half life

the time it takes for the raidioactivity of a certain isotopes to fall half its orgiginal value

period

one of the units of geologic time in to which geologist divide the eras

radioactive decay

the breakdown of a raidioactive element releasing particles and energy

raidiometric dating

a method of dating geological or archaeological specimens by determining the relative proportions of particular raidioactive isotopes present in a sample.

relative age

the age of a rock compared to the ages of rock layers surrounding it

unconformity

a place where an old eroded rock surface is in contact with a newer rock layer

uplifting

when an area is raised higher than the surrounding landscape due to tectonic forces