Basic principles for relative geologic dating

Igneous rocks from the cooling of molten material magma, lava and are rich in silicate minerals. Molten material derived from deep in the Earth's mantle is typically enriched in iron- and magnesium-rich silicate minerals and the rocks they form, these are called mafic or ultramafic. In contrast, magma and lava associated with continental crustal regions are enriched in felsic silicate minerals rich in silicon and aluminum mostly feldspars The importance of felsic and mafic minerals are introduced below. This contrast between mafic and felsic materials is important to discussion about plate tectonics in Chapter 5. Igneous rocks Fig. Sediments Fig.

This page has been archived and is no longer updated. Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4. Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free. These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this instant, the Earth's surface is moving and changing. As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils.

Nicolaus Steno introduced basic principles of stratigraphy , the study of layered rocks, in William Smith , working with the strata of English coal Former swamp-derived plant material that is part of the rock record. The figure of this geologic time scale shows the names of the units and subunits. Using this time scale, geologists can place all events of Earth history in order without ever knowing their numerical ages. The specific events within Earth history are discussed in Chapter 8.

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