Difference between relative absolute dating

In this lesson we'll discuss both absolute and relative time, and how they work together to give us a detailed history of Earth.

How much of your life do you spend thinking about time? Time comes in different forms in geology, mainly absolute and relative.

These relations may be expressed as either absolute or relative differences.

An absolute difference is a subtraction; a relative difference is a ratio.

For example, the statement, "The risk for disease X was cut in half" gives no information about where you started.

(NB: Relative risk, relative rate, rate ratios, and odds ratios are all examples of relative differences.) Given the data above, the relative difference is: Expressed as a relative difference, intensive therapy reduces the risk for blindness by half. Without any qualification, both statements ("reduced the risk by 1%" and "reduced the risk by 50%") could be construed as representing either an absolute or relative difference.

But most important, note the difference in "feel." A statement of "reduced the risk by 1%" does feel like a smaller effect than "reduced the risk by 50%." The most frequent problem readers will face is the reporting of an isolated relative difference.

Angular unconformity – tilted rocks are overlain by flat-lying rocks b. William Smith (late1700s–early 1800s) noted that sedimentary strata in widely separated areas could be identified and correlated by their distinctive fossil content 2.

Disconformity – strata on either side are parallel c. Principle of fossil succession – fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content a.

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