Principles of radiometric dating

19-Dec-2019 19:21 by 6 Comments

Principles of radiometric dating

Paleontology is the study of fossils and is concerned not only with their description and classification but also with an analysis of the evolution of the organisms involved.Simple fossil forms can be found in early Precambrian rocks as old as 3,500,000,000 years, and it is widely considered that life on Earth must have begun before the appearance of the oldest rocks.

Today biostratigraphy uses fossils to characterize successive intervals of geologic time, but as relatively precise time markers only to the beginning of the Cambrian Period, about 540,000,000 years ago.Certain common objects that have been assigned hardness values roughly corresponding to those of the Mohs scale (e.g., fingernail [2.5], pocketknife blade [5.5], steel file [6.5]) are usually used in conjunction with the minerals on the scale for additional reference.Other physical properties of minerals that aid in identification are crystal form, cleavage type, fracture, streak, lustre, colour, specific gravity, and density.Geochemistry is the study of the composition of these different types of rocks.During mountain building, rocks became highly deformed, and the primary objective of structural geology is to elucidate the mechanism of formation of the many types of structures (e.g., folds and faults) that arise from such deformation.Geologic history provides a conceptual framework and overview of the evolution of the Earth.

An early development of the subject was stratigraphy, the study of order and sequence in bedded sedimentary rocks.

Thus a few minerals such as the feldspars, quartz, and mica are the essential ingredients in granite and its near relatives.

Limestones, which are widely distributed on all continents, consist largely of only two minerals, calcite and dolomite.

Determining the Mohs scale of hardness, which lists 10 common minerals in their relative order of hardness: talc (softest with the scale number 1), gypsum (2), calcite (3), fluorite (4), apatite (5), orthoclase (6), quartz (7), topaz (8), corundum (9), and diamond (10).

Harder minerals scratch softer ones, so that an unknown mineral can be readily positioned between minerals on the scale.

This in turn helps in interpreting the mode of formation and the depositional environment of sedimentary rocks.

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