Most useful isotopes used in geological dating
Ever since The Enlightenment, and possibly even before that, researchers have attempted to understand the chronology of the world around us, to figure out precisely when each stage in our geological, biological and cultural evolution took place. Even when the only science we had to go on was religious literature and the western world believed the world was created in BC 1 , scholars tried to figure out when each biblical event took place, to define a chronology from savagery to civilization, from creation to the first animal, then to the emergence of the first people. The pre-enlightenment understanding of our geological and cultural history may now be proven wrong and subject to ridicule, but the principles of defining our place in time in the cosmos underpin many sciences. As technology advances, so do our methods, accuracy and tools for discovering what we want to learn about the past. All dating methods today can be grouped into one of two categories: absolute dating , and relative dating. The former gives a numeric age for example, this artefact is years old ; the latter provides a date based on relationships to other elements for example, this geological layer formed before this other one.
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Proxy Techniques: Stable Isotopes, Trace Elements and Biomarkers | EARTH Earth in the Future
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide ; it is moderately hard, malleable , and has a high melting point. All known thorium isotopes are unstable. The most stable isotope, Th, has a half-life of On Earth, thorium and uranium are the only significantly radioactive elements that still occur naturally in large quantities as primordial elements. Its first applications were developed in the late 19th century. Thorium's radioactivity was widely acknowledged during the first decades of the 20th century.
RADIOMETRIC TIME SCALE
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Geologists often need to know the age of material that they find. They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of years. This is different to relative dating, which only puts geological events in time order. Most absolute dates for rocks are obtained with radiometric methods. These use radioactive minerals in rocks as geological clocks.