Geology
From RationalWiki
The science of geology ranges from the study of individual rocks, to the study of the composition of the entire Earth. In between, geologists work to explain why the suface of the land looks the way it does, where valuable mineral resources might be found, how the land used to look based on the minerals deposited there, and how the continents have moved over time, creating new mountain ranges and oceans. Much to the dismay of Fundamentalist Christians, all of this provides evidence for the fact that this is a very old planet. Indeed it would be very difficult to conduct any sort of mineral exploration using a young-Earth hypothesis.
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[edit] Rocks
Rocks are made of minerals. Minerals consist of crystals. New rock is produced by the welling up of molten magma from inside the earth via volcanoes and other rifts in the planet's surface. Such igneous (formed by fire) rock has very small crystals if it cooled rapidly (near or on the earth's surface), as can be seen in basalt. When magma cools far under the surface of the earth the crystals form very slowly and are much lager, as for example, the large crystals of quartz, mica and feldspar that are visible in granite.
Over time the action of erosion through temperature changes, rain, wind, and the moving action of streams and rivers, breaks igneous rock down into smaller and smaller pieces. These are washed downstream and eventually deposited in an ocean or lake. Again, over thousands of years, layers of minerals that have been deposited are accumulated to depths that work to press lower layers together with enough pressure to fuse them into stone. Pieces of quartz from eroded granite, for example, are deposited in beaches and the ocean floor near a continent, and eventually form sandstone. Rock that is made of an accumulation of very fine pieces of eroded rock is called sedimentary rock.
Through the action of the movement of the earth's crust, particulary when continents collide or when the earth's crust is pulled downwards towards the interior in a process called subduction (more about this later), rocks of any kind can be subjected to such enormous pressure and heat that they are transformed into a new kind of rock, called metamorphic rock. Sandstone that has been subjected to these metamorphic forces can be transformed into a very hard rock called quartzite.
[edit] Plate Tectonics
Extensive exploration and mapping of the seafloor after World War II led to the discovery of a deep rift running down the center of the Mid-Atlantic Ridge. In the early 1960s Harry Hess of Princeton University and Robert Dietz of the University of California suggested that the seafloor separates along the rifts in mid-oceanic ridges and that new seafloor forms by upwelling of hot mantle materials in these cracks, followed by lateral spreading. By 1967, separate lithospheric plates had been identified, which explained phenomena such as high levels of volcanic and earthquake activity that take place between the plates. By the end of the 1960s the theory of plate tectonics proved to be a unifying concept that pulled together diverse theories and explained a the large body of observations in the field. [1]
Twelve or so plates slide over a partially molten lithosphere, and the continents, embedded in some of the plates, are carried by them. Where plates collide, mountains such as the Himalayas or the Rocky Mountains are formed. In some places, called subduction zones one plate sinks beneath another plate and returns to the molten regions of the athenosphere. Along mid-oceanic ridges magma emerges to expand the plate and create new sea floor.
[edit] Composition of the Earth
Volcanism and deformation bring rocks to the surface of the Earth from depths as great as 50 to 100 km. Scientists can make inferences about some of the properties of the Earth at these depths by studying these rocks. But far more information has been provided through the use of seismic waves created by natural earthquakes, and by controlled explosions designed to learn more about the composition of the Earth, including underground nuclear explosions. This data has revealed that the Earth is composed of three main layers, the crust, the mantle and the core. The crust, or outermost layer, varies in thickness from about 5 km under oceans to about 40 km under continents. The mantle consists of an outermost zone of about 100 km thick named the lithosphere. The layer below is a partially fluid solid named the athenosphere, which ends at a depth of about 200 km. As seismic waves penetrate deeper into the mantle they indicate that between 400 km and about 2900 km atoms are packed closer and closer together by extreme pressures, creating a crystalline structure. The Earth's core is 2900 km from the surface. Seismic waves slow down in this region until a depth of 5100 km, indicating that the core consists of a liquid layer surrounding a solid core at the center.
[edit] Age of the Earth
It is 4.6 billion years old. Creationists, deal with it.
