The Rock Record

Chapter 8

itarianism

A principle that geologic processes that occurred in the past can be explained by current geologic processes. Volcanism and Erosion

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Relative Age

The age of an object in relation to the age of other objects

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The law that a sedimentary rock layer is older

than the layers above it and younger than the layers below it if the layers are not distrubed

Law of Superposition

Oldest

Newest

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A break in the geologic record created when

rock layers are eroded or when sediment is not deposited for a long period of time.

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conform

Absolute Age

The numeric age of an object or event, often stated in years before the present.

Using a process like “radiometric dating” or “carbon dating”

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Rates of Deposition

In general, about 30 cm of sedimentary rock are deposited over a period of 1,000 years.

However, a flood can deposit many meters of sediment in just one day.

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Radiometric Dating

A method of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) and a stable (daughter) isotope.

Half-Life: the time required for half of a sample of a radioactive isotope to break down.

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Carbon-14 Dating

Plants absorb Carbon during Photosynthesis

Scientists compare the carbon isotopes 12C and 14C (radioactive)

This can be used to determine the ages of wood, bones, shells and other organic remains that are less than 7,000 years old.

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Pa

leonto

log

y The scientific study of fossils.

Trace Fossils

Fossilized evidence of past movement of an animal such as tracks, footprints, borings and borrows.

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Index Fossils

A fossil that is used to establish the age of rock layers because it is: Distinct – features different from other

fossils Abundant – occurs in fairly large

numbers Widespread – present in scattered rocks Existed only for a short span of

geologic time

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Eras & Periods

Precambrian makes up about 88% of Earth’s history!

Most rocks from that time have been severely deformed and altered by plate tectonics.

Fossils are rare because life-forms lacked bones, shells or other hard parts to make fossils.

The most popular Precambrian fossils are Stromatolites.

Precambrian

Paleozoic

Mesozoic

Cenozoic

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Eras & Periods

Fossils of the first vertebrates appear (Paleo…)

Most fossil fuels (coal and oil deposits) formed during the Carboniferous Period.“Carbonization” is the term for how plant remains were turned into coal and oil..

The Super-Continent “Pangea” formed at the end of this era – about 250 million years ago!

Precambrian

Paleozoic

Mesozoic

Cenozoic

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Eras & Periods

Mesozoic: known as the Age of Reptiles

Dinosaurs first appeared during the Triassic Period, but they really dominated in the Jurassic Period.

Dinosaurs supposedly became extinct when a giant meteorite crashed into Earth (impact hypothesis).

Precambrian

Paleozoic

Mesozoic

Cenozoic

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Eras & Periods

Cenozoic Era is known as the Age of Mammals.

Human civilization developed during the Quaternary Period.

Precambrian

Paleozoic

Mesozoic

Cenozoic

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