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Morrison Formation

Cross-sectional diagram illustrating plate tectonics, showing oceanic and continental crust moving over the asthenosphere. It highlights divergent boundaries at oceanic ridges where crust forms, convergent boundaries at trenches with subduction zones where crust is destroyed, and a transform boundary with a fault. Features such as island arcs, rising magma, and hotspots are labeled.

Diagram explaining Steno's four laws of stratigraphy in geology, with labeled illustrations for the law of superposition, original horizontality, cross-cutting relationships, and lateral continuity, showing how rock layers form and are altered.

Cutaway diagram of a Grand Canyon wall showing layered sedimentary rocks-limestone, shale, sandstone, and composite rocks-with labels indicating Paleozoic rocks (about 252-541 million years old) above older Precambrian rocks, which include Proterozoic (541 million to 2.5 billion years old) and Archean (over 2.5 billion years old) layers. The Colorado River is shown at the base.

A detailed geologic time scale chart displaying Earth's history from the Hadean Eon over 4.5 billion years ago to the present, organized by eons, eras, periods, epochs, and ages with color-coded columns and corresponding dates in millions of years.

isochron diagram

titanite discordia

Learn how the radiometric rubidium-strontium dating technique is used to determine the age of rock particles

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Topics

obsidian–hydration–rind dating absolute dating cross dating Blytt–Sernander system varve analysis stratigraphic correlation sequence determination relative dating tephrochronology radiometric dating Excavation fossil record index fossil Today in History—November 16: The Accidental Discovery of the Hoxne Hoard Today in History—April 28: Chinese Tomb Discovery Upends the History of Paper A Journey Through Time Since the Precambrian Egyptology ley lines Today in History—September 12: The Discovery of the Lascaux Caves What is the difference between archaeology and paleontology?

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Key People

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Loren Eiseley

American anthropologist

Sir Flinders Petrie, detail of an oil painting by George Frederic Watts, 1900; in the National Portrait Gallery, London.

Sir Flinders Petrie

British archaeologist

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Édouard Lartet

French geologist and archaeologist

Boucher de Perthes, Jacques

Jacques Boucher de Perthes

French archaeologist

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Esther Boise Van Deman

American archaeologist

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Per Teodor Cleve

Swedish chemist