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The idea that laws in science that "work" in our world today also "worked" in the past.

Law of superposition

Within the layers of undisturbed rock, the oldest layers are on the bottom and the youngest layers are on top.(Refers to relative not numerical dating)

Principle of horizontality

Layers of sedimentary rock are laid down horizontal and this implies that if we find a rock where the layers are not horizontal some geological event has happened since their formation.

principle of cross cutting relationships

Igneous intrusion or a fault which cuts across

What kind of layers form when two distinct layers of sedimentary rock meet?

Layers are conformable or an unconformity exists.


Layers were laid down uninterrupted by time


Exists when the bottom layer is eroded before the next layer is laid down.

3 categories that unconformities are put in?

Angular, Disconformity, noncomformity

What is correlation or matching of rock layers at different points based on? (3)

Stratigraphy (order of layers), fossils in the layers, and types of rocks in the layers.

Study of fossils?



The remains or traces of once living things preserved in a rock structure.

Index fossils represent?

Organisms that as a species had a relatively short existence on the geological time scale and are found in wide spread geographical places.


Atoms of the same substance with different numbers of neutrons

Nuclear radiation or radioactivity?

The particles or energy being released to create stability.

Nuclear decay?

when the nucleus gives off radiation and becomes smaller.

In Nuclear decay, the specific time that an _______ nucleus will decay is not predictable but the amount of decay in a ______ of nuclei is predictable.


Half life? Is this linear?

The amount of time that it takes for 1/2 of sample of similar radioactive isotopes to decay. No it's exponential.

Carbon 14

One of the first radiometric substances used for numeric dating.

Potassium 40


Span of time sub divisions?

Eons, eras, periods, epochs.

4 eon names?

Phanerozoic, Hadean, Archean, and proterozoic

largest section of the time scale?


What life appeared in the Precambrian period first? It developed to?

One celled organisms sin nuclei (prokaryotes)
Multi celled organisms con distinct nuclei (eukaryotes)

Paleozoic Era= Age of____ (3)
Besides animals, what else began to develop?

Invertebrates. Fishes. Amphibians.

Most common invertebrate animal in the Paleozoic period?


Mesozoic era= Age of ____ or _____

Reptiles or Dinosaurs

When did Pangaea break?

During the mesozoic era

How did the Mesozoic era end?

Extinction of dinosaurs.

Cenozoic era= ___era or Age of the ____

Our. Mammals

Humans are considered ____


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