Rey writer

Geology is science that studies all physical aspects of the planet Earth and other planets. It is the

study of the history of the planet, the composition, the internal structure and the surface features of

that planet. We study our planet by field work, sample collecting and mapping. The samples can be

analyzed via chemical means as well as by optical means. Fossils are identified and correlated to age

and paleo-environments. Other related Earth sciences that are closely related to geology are

meteorology, oceanography and ecology. Subfields of geology are geochemistry, geophysics and

geo-biology. Other planets we study via remote sensing and by studying analysis sent by rovers of

samples that they have collected.

While geology is lumped as earth science and taught in high school to those who can't handle

science like biology, chemistry or physics. In reality geology is a hybrid science requiring calculus,

chemistry through at least p-chem., and physics. On top of this knowledge add to it an

understanding of earth processes, mineralogy, and optics. Paleontology also requires knowledge of

biology as well.

Geologists are taxed with finding oil and coal for energy to power our modern economy. But this

is not only task that the geologist serves. Every bit of metal you use, every mine that is dug depends

of geologist. Modern batteries that may give us energy independence, materials used to build

photovoltaic cells and wind turbines are courtesy of geologist.

How does a geologist study the earth? Are we out there with rock hammers in hand and a pack

mule behind us? We use the same method as all other scientist- the scientific method. This method

calls for a hypothesis (possible explanation) for an event or series of events that have been

observed. A coherent set of hypothesis back by a large by of data both observational and by

laboratory measurements gives theory to explain a series of events. These theories obey the

physical laws or principles of how the universe works. Please notice that one part of the scientific

method is missing- experimentation in a controlled environment. It is impossible to do this when the

events we are theorizing about are global in nature and take place of millions to billions of years. To

deal with that we turn to the scientific model and create mathematical models that we try to

simulate what the Earth will do during time.

We use knowledge the data that formed the hypothesis and theories into a mathematical model

run through a computer to test the validity of our theories. But remember it is the same technique

that forecast the local weather. To improve the theory and model we continue to gather data. This

data is not only based on observations in the field (our geologist with the mule) but by using remote

sensing using satellite data, chemical and optical analysis of rocks.

From observation can the principle of uniformitarianism that can be paraphrased by the

statement that the present is the key to the past. The forces acting on our planet today are the same

forces that have acted on it in the past. This covers the slow steady process such as river moving

sediment to the ocean and the wind eroding a rock into strange shapes. It also allows for the

cataclysmic event like the earthquake, volcanic eruption and meteor impact. Most geologic process

takes thousands to millions of years, though.

The first part of understanding geology is understanding the makeup of the planet itself. The

size of the planet was determined 250 BC by a Greek performing an experiment. His estimate of

40,000 km with a radius of 6370 km and was surprisingly accurate. A more precise measurement

was achieved in the 1800's found that the earth is not a perfect sphere. It bulges out slightly at the

equator and is smashed slightly at the poles.

The Earth is not a smooth sphere as it appears in

space. Instead it is broken by mountains and valleys.

This is called topography and is measured with respect to

sea level (sea level is considered 0). Our planet varies

from 0 to 1 km above sea level and 4 to 5 km below sea

level. This topography was created by forces acting in the

Earths depths.

The Earth's density gave the first clue to the different

layers in the interior of the earth. Our planets volume was

known by knowing its radius (πr2) discovered in 250 BC. Its density was calculated in 1789 by from

the force of gravity that pulls objects to the surface. A German physicist Emil Wechert knew that

the average crustal rock like granite had a density of

2.7g/cm 3 . The planets density was measured at

5.5g/cm 3 . The heaviest rocks found on the planet was

found to be rich in iron and brought to the surface by

volcanoes. It only had a density of 3.5g/cm3.

He looked down at his feet and proposed an idea that would explain this difference. He knew

that some meteorites were a mixture of two heavy atoms, nickel and iron (density of 8g/cm 3 ). If the

outer portion of the planet was light then the inner portion must be composed of the heavier

materials. The idea of a light crust on the planet surrounding a heavier core was proven by

examining the seismographs to see if there were changes in the waves as they passed into the earth.

This theory was proven correct in 1906 by Englishman Robert Oldham with the use of seismic

waves. There are two seismic waves that can penetrate the body of the planet. One of these waves

can penetrate both solids and liquids, the other only through liquid. (assignment 1,

http://www.classzone.com/books/earth_science/terc/content/investigations/es0402/es0402page0

1.cfm) By noting the missing seismic wave at different seismograms he could map a liquid core. He

discovered that the fact that deep in the earth was a molten layer. Here the planet was hot enough

to melt nickel and iron but not silicate based rocks. This explained the discrepancies in mass.

Prior to this was discovered another phenomena- the Moho Discontinuety. This was a change in

seismic wave speed as it entered the earth’s depths. Seismic waves travel slower in less dense

material. Our crust was made up of material that is less dense then the material beneath it. This

outer material, the mantel, is made up of minerals containing magnesium and iron, while the crust

minerals were mainly made up of silicate mineral composed of potassium and aluminum. Our crust

was surrounding a much denser material and our continents were found to "float" one this denser

mantle.

Courtesy of the cold war and seismic stations spread throughout the world (to monitor nuclear

testing) all of the major Earth layers had been discovered. The composition of these layers was

estimated by their densities. This density was determined by the change in speeds of the seismic

waves. Look at the figure on page 41 to see what makes up our planet. These are the main

elements that compose the planets with the other elements being present in trace amounts.

Our planet then is constantly changing under the influence of two "engines". The internal engine

is powered by the internal heat from our planet. The external or surface of our planet is powered by

the Sun. The combination of these two driving forces comprises the Earth system. This system is an

open ended system exchanging mass and energy within itself and with its surrounding

Solar energy powers our weather creating weathering and erosion of the earth’s surface and

powers the growth of plants. Our climate is controlled by a balance of solar energy and the energy

of Earth radiates back into space. Mass is exchanged back and forth between Earth and space. We

get mass from meteors. In fact our planets origin is as an assembly of small bodies such as meteors,

asteroids and comets. The Earth, in turn, loses molecules such as water escape into space.

Earth is divided into spheres. The external spheres are energized by solar radiation. The external

spheres are the following: 1. atmosphere, 2.hydrosphere, 3. cryosphere, 4. biosphere. The internal

spheres are the following: 1. lithosphere (rock layer)

composed of the upper ridged mantel and the crust, 2.

asthenosphere or plastic sphere, 3. deep mantel, 4.

inner and outer core.

The last two spheres the deep mantel and the core

form the Geodynamo System. This system controls the

magnetic field. The first two internal spheres control

the formation of new sea floors, new land masses,

mountains and can increase the sea level. These

processes explain the phenomena known as Plate

Tectonics.

The magnetic field is formed by the heat transfer from the inner core to the outer core which

creates convection currents in the outer core. The rapid motions from the currents stir the liquid

inner core up and electric currents form in the liquid outer core. The magnetic fields create both the

north magnetic pole which is off the earth’s axis by 11 degrees and the South Pole. This magnetic

field protects us from solar radiation. This increase radiation would increase cancers in adults, kill

phytoplankton, and injure all life forms. The interesting thing about this is that this field reverses

itself every tens of thousands to millions of years. There is no full extinction event seen at these

reversals.

Plate tectonics is driven by the internal heat, just as the geodynamo. Here the heat passes up

from the inner core, through the lower mantel to the asthenosphere. This plastic layer

(asthenosphere) develops convection currents that splits the lithosphere. It also causes volcanoes

and earthquakes while building land masses and destroying sea floor. The mountains that where

created impacts the uppers spheres, areas of the atmosphere, hydrosphere, cryosphere and

biosphere. The formation of new sea floor and its destruction impacts the biosphere and

hydrosphere.