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By measuring the ratio of parent to daughter isotopes in the mineral and comparing it with the rate of radioactive decay, we can determine the numerical age of a rock. Types of Isotope Dating We pick dating methods based on approximate age of the rock and the rock composition Old rocks – long half lives Young rocks – short half lives Composition: have to use a dating method corresponding to what is in the rock I. drought) causes distinct patterns that can then be correlated between trees Useful for dating: landslides, avalanches, or mudflows or wooden artifacts I. Other Dating Techniques: Besides isotopic methods A.

Dendrochronology (Tree-ring dating)Trees grow rings for each year We can count rings to get ages of trees Pronounced changes in climate (i.e.

A second assumption that geologists make regarding relative dating is that the oldest rock layers are closest to the bottom, and the newest layers are closest to the top.

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The plane or junction, marked by the thick green line, between both sets of strata is the unconformity.At Thornton Force the junction is marked by a basal conglomerate. When found in rocks as far away as Australia you could reasonably expect those rocks to be the same age as those in Cliviger Valley!A third fact emerges from the study of stratigraphy - the UNCONFORMITY.The laws of physics and chemistry that governed geologic processes in the past are the same as those that govern processes now and in the future.

The geologic timescale is a chronology (calendar) of events on Earth based on obtaining ages of past events.Atomic Mass = protons neutrons Can change in different atoms of the same element5. Percentage of parent atoms that decay in each half life is the same (50%)The actual number of atoms that decay with each passing half-life continually decreases I.Isotopes: atoms of the same element (same atomic #), with different # of neutrons For example Oxygen (8 protons): 8 neutrons 16O9 neutrons 17O10 neutrons 18OC. Principles of Numerical Dating Increase in daughter = decrease in parent I.These ages have been derived from relative dating and absolute dating (radiometric dating) of rock layers and fossils.(a) Relative Dating This technique uses principles of stratigraphy (rock strata) and the study of fossils (palaeontology) to determine the relative ages of rocks and sediments. Field geologists' rely on a number of simple techniques for dating rocks and constructing geological successions. The Law of Strata Identified by Fossils is a little bit more complex.(relative geologic timescale) (b) Absolute Dating Following the discovery of radioactivity in 1895, radiometric dating techniques were developed to determine the absolute ages, i.e. In the succession of strata, each layer represents the geographical conditions that occurred over that area at the time the layer was deposited.