Concepts of relative dating
Rock form in a variety of geologic setting ranging from locations on or near the earth surface, deep underground, or even in outer space.Most of the rocks we see on the surface of the planet formed by processes that happened long ago, but we can see these processes actively taking place in many places.For example, the element carbon has 3 isotopes: C is unstable and will undergo radioactive decay.All there isotopes have 6 protons, but have 6, 7, and 8 neutrons, respectively.The lightest element, hydrogen, has one proton, whereas the heaviest naturally occurring element, uranium, has 92 protons. Isotopes are each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties.Some isotopes are not stable and ultimately break down or change in other elements.The Periodic Table is a list of 108 known elements arrange by atomic number (see Figure 2-6).
The chemical characteristics of earth materials are reflect the environments how and where they are formed, they also determine their potential fate when exposed to chemical changes.Rapid rock formation can be seen happening such as lava cooling from a volcanic eruption in places like Hawaii or Iceland.However, most rocks we see around us form very slowly in settings that are not visible on the land surface.It is conceptually important that each rock has an origin in concepts of place, time, and physical and chemical conditions. These changes may be rapid (such as a volcanic explosion) or gradual, taking place over millions or billions of years, and involving movement over great distances, both at the surface or to deep within the Earth's crust below us.Trying to explain the what, how, and when of a rock's journey is fundamental to explaining why rocks are significant to resolving questions about our Earth's history and conditions within the physical environments where we live.