How do relative and radioactive dating work

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He also found that certain animals were in only certain layers and that they were in the same layers all across England.Due to that discovery, Smith was able to recognize the order that the rocks were formed.The Law of Superposition, which states that older layers will be deeper in a site than more recent layers, was the summary outcome of 'relative datin g' as observed in geology from the 17th century to the early 20th century.The regular order of the occurrence of fossils in rock layers was discovered around 1800 by William Smith.A fundamental principle of geology advanced by the 18th century Scottish physician and geologist James Hutton, is that "the present is the key to the past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now." The principle of intrusive relationships concerns crosscutting intrusions.In geology, when an igneous intrusion cuts across a formation of sedimentary rock, it can be determined that the igneous intrusion is younger than the sedimentary rock.Relative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age (i.e. In geology, rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another.

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The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds.

Geologists still use the following principles today as a means to provide information about geologic history and the timing of geologic events.

The principle of Uniformitarianism states that the geologic processes observed in operation that modify the Earth's crust at present have worked in much the same way over geologic time.

Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization (although cross-bedding is inclined, the overall orientation of cross-bedded units is horizontal).

The law of superposition states that a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it.

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