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Flashcards in Chapter 23 Deck (14):

Paleozoic era

The time of ancient life from about 543 million years ago to 248 million years ago



The late Paleozoic supercontinent made up of Gondwanaland and Laurasia



Time gaps in the rock record caused by erosion of pre-existing rock or by an interruption in the sequence of deposition


Crosscutting relationships

And igneous intrusion or fault that cuts through pre-existing rock is younger than the rock through which cuts


Relative dating

The ordering of rocks in sequence by their comparative ages


Precambrian time

The time of hidden life which began about 4.5 billion years ago when earth formed, lasted until about 543 million years ago


Lateral continuity

Sedimentary layers are deposited in all directions over a large area unless some sort of obstruction or barrier limits their deposition. Faulting, folding, and erosion can separate originally continuous layers into isolated outcrops



In an undeformed horizontal sequence of sedimentary rocks, each layer is older than the one above and younger than the one below. Like the newspapers in a recycling bin, all the papers are found below newer, more recent papers


Radiometric dating

A method for calculating the age of geologic materials based on the nuclear decay of naturally occurring radioactive isotopes


Cenozoic era

The time of recent life which began 65 million years ago and his ongoing. Also known as the age of mammals


Faunal succession

Fossil organisms follow one another in a definite, irreversible time sequence. Fossil communities change through time at some species become extinct in new ones up here. Such changes are reflected in the rock record. In this way, fossils provide a key to for recognizing the relative ages of rock


Mesozoic era

The time of middle life, from about 248 million years ago to 65 million years ago. Also known as the age of the reptiles



Inclusions are pieces of one rock contained within another. Any inclusion is older than the rock containing it just as small pieces of rock Inc. in a slab of concrete or formed before the concrete was formed


Original horizontality

Layers of sediment are deposited horizontally. layers that are tilted or fold must have been moved into that position by disturbances such as earthquakes and mountain building, after deposition