Relative dating of rocks and events

PALEONTOLOGY, AND in particular the study of dinosaurs, is an exciting topic to people of all ages.

Although most attention in today's world focuses on dinosaurs and why they became extinct, the world of paleontology includes many other interesting organisms which tell us about Earth's past history.

If the letters "T" and "C" represent fossils in the oldest rock layer, they are the oldest fossils, or the first fossils formed in the past for this sequence of rock layers. Now, look for a card that has either a "T" or "C" written on it.

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In this activity, students begin a sequencing activity with familiar items — letters written on cards.

Once they are able to manipulate the cards into the correct sequence, they are asked to do a similar sequencing activity using fossil pictures printed on "rock layer" cards.

This relative time scale divides the vast amount of earth history into various sections based on geological events (sea encroachments, mountain-building, and depositional events), and notable biological events (appearance, relative abundance, or extinction of certain life forms).

Objectives: When you complete this activity, you will be able to: (1) sequence information using items which overlap specific sets; (2) relate sequencing to the Law of Superposition; and (3) show how fossils can be used to give relative dates to rock layers.

The Law of Superposition, which states that in an undisturbed horizontal sequence of rocks, the oldest rock layers will be on the bottom, with successively younger rocks on top of these, helps geologists correlate rock layers around the world.

This also means that fossils found in the lowest levels in a sequence of layered rocks represent the oldest record of life there.

Scientists also use direct evidence from observations of the rock layers themselves to help determine the relative age of rock layers.

Specific rock formations are indicative of a particular type of environment existing when the rock was being formed.

Sequencing the rock layers will show students how paleontologists use fossils to give relative dates to rock strata.

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