Introduction to Geology
by Dave Van Dieren
The most basic understanding of geology starts with an understanding of the structure of the earth. It may seem odd but the rock we are standing on is floating on a layer of liquid lava. Since the rock is floating in liquid it is free to move up and down and sideways depending on the forces under the crust. Below is a diagram that shows the best understanding of the internal structure of the planet earth.
Plate Tectonics
The understanding of the movement of the solid crust of earth is the theory of plate tectonics and how the movement of the plates are driven by convection currents. The diagram below show how the different crustal plates can move relative to each other. The diagram after shows how convection currents drive the movement of the crustal plates.
There are three types of plate boundaries. They are each associated with different types of surface phenomena and are characterised by the way the plates move relative to each other. The different types are transform boundaries (which occur where plates slide past each other), divergent boundaries (which occur where two plates slide apart from each other) and convergent boundaries (where plates slide towards each other).
Rights: Jose F. Vigil, US Geological Survey (USGS), Public Domain
Published: 9 April 2010Size: 124.63 KB
Convection Currents - 8TH-GRADE SCIENCE
The following diagram shows how the plates in the earth’s crust are moving relative to each other. Basically the Atlantic Ocean is getting bigger as the plates spread apart while the Pacific Ocean is getting smaller as the plates move together.
The continents have split apart from what was formerly the supercontinent Pangea (320 million years ago) but are slowly moving together to reform a new supercontinent. The cycle repeated at least twice before the formation of Pangea.
The Pacific Ocean is getting smaller resulting in subduction zones along the west coast of North and South America and the coast of Asia. These subduction zones, see next diagram, result in the formation of mountain ranges and active volcanic areas along the continental margins.
Faulting
As a result of stress on the plates there is movement of the rocks within the continental plates and this is called faulting. There are three types of faults as shown in the following diagram.
Geologic Timescale
All this talk about moving rocks and continents it is time to look at the age of the earth. Most Geologic timescale charts are logarithmic giving the false impression that complex life on earth has been around the majority of the time since the formation of the earth. This is not the case, so have have selected a time scale chart that is not distorted.
The earth formed about 4.55 billion years ago and complex live formed rapidly just 530 million years ago (0.53 billion years) known as the Cambrian explosion. Homo sapiens have only walked the earth for less than 300 thousand years. Since humans are so recent we do not appear as a line on the timescale!