The tectonic plates are the large pieces of rock under the earths surface that are constiantly shifting and that cause earthquakes and volcanic eruptions the earth has several layers;the core,mantle and crust which has rocks.the mantle contains molten metalic liquid we call magma.the rocks in the crust are not completely joined but separated by bounderies that we call tectonic bounderies.and those rigid pieces joined are what we call tectonic plates that float on the mantle. tectonic plates are giant slabs of rock under the surface of earth that constantly shifting and the can create earthquakes , and volcanic eruptions
Volcanoes are generally found where two to three tectonic plates
diverge or converge. The mid-oceanic ridges, like the Mid-Atlantic
Ridge, are typical examples of divergent tectonic plates where volcanoes
are formed, whereas the Pacific Ring of Fire is a typical example of
volcanic activity on convergent tectonic plates. Where two tectonic
plates slide past one another (like the San Andreas fault) volcanic
activity is generally not found.
Volcanic activity can also occur from mantle plumes, the so-called hotspots, which occur at locations far from plate boundaries; hotspot volcanoes are also found elsewhere in the solar system, especially on its rocky planets and moons. In July 2006, a new type of volcano was discovered, which was called a petitspot, to accentuate the difference with volcanoes formed by mantle plumes.
On locations where tectonic plates diverge or converge, volcanoes can be found. A volcano consists of a deep magma chamber where magma accumulates, pipes that lead to surface vents, and the vents through which lava is emitted during a volcanic eruption. Volcanoes are often known to have a mountain-like shape. Volcanoes that have not erupted for some time are dormant, and volcanoes that have not erupted even in the distant past are called extinct. Volcanic activity and volcanic eruption is usually triggered by alterations of tectonic plates, resulting in landslides or earthquakes.Volcanic eruptions can be extremely damaging to the environment, particularly because of a number of toxic gases possibly present in pyroclastic material. It typically consists mainly of water vapour, but it also contains carbon dioxide and sulphur dioxide gas. Other gases typically found in volcanic ashes are hydrogen sulphide, hydrogen chloride, hydrogen fluoride, carbon monoxide, and volatile metal chlorides.
dating by superposition
It states that in undisturbed strata the layers on bottom must be older than those on the top.
Therefore, fossils in older layers must be older than fossils in younger layers. once we assume that all rock layers were originally horizontal we can make another assumption that the oldest rock layer are furtherest towards the bottom and the youngest rock layer are closest to the top . this is called the dating by superposition.
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