Earth is the mighty planet upon which we all live. Only recently have humans begun to understand the complexity of this planet. In fact, it was only a few hundred years ago that we discovered that Earth was just a tiny part of an enormous galaxy, which in turn is a small part of an even greater universe. Earth science deals with any and all aspects of the Earth. Our Earth has molten lava, icy mountain peaks, steep canyons and towering waterfalls. Earth scientists study the atmosphere high above us as well as the planet's core far beneath us. Earth scientists study parts of the Earth as big as continents and as small as the tiniest atom.

In all its wonder, Earth scientists seek to understand the beautiful sphere on which we thrive.

Figure 1: Earth as seen from Apollo 17.

(Source: http://en.wikipedia.org/wiki/Earth, License: GNU-FDL)

Introduction

The Earth is part of the universe. The universe itself is a limitless space around us. The universe consists of innumerable clusters of heavenly bodies and galaxies, which contain billions and billions of stars. Of the bodies and galaxies, which make up the universe, solar system is one of the most important. The solar system is one of the smallest and it is commonly known as "milky way".

Earth (planet), one of the planets in the solar system, the third in distance from the sun and the fifth largest of the planets in diameter. The mean distance of the earth from the sun is 149,503,000 km (92,897,000 mi). It is the only planet known to support life, although some of the other planets have atmospheres and contain water.

The diameter of the earth, measured around the equator, is about 12756 km (7926 mi). The earth is not a perfect sphere but is slightly oblate, or flattened at the poles. Because of this flattening, the diameter of the earth measured around the North Pole and the South Pole is about 12713 km (7899 mi) - 43 km (27 mi) less than the equatorial diameter.

Age and origin of the earth

Radiometric dating has enabled scientists to arrive at an estimate of 4.65 billion years for the age of the earth (see Dating Methods). Although the oldest earth rocks dated this way are not quite 4 billion years old, meteorites, which correlate geologically with the earth's core, give dates of about 4.5 billion years, and crystallization of the core and meteorites is considered to have occurred at the same time, some 150 million years after the earth and solar system first formed (see Solar System: Theories of Origin).

After originally condensing, by gravitational attraction of cosmic dust and gas, the earth would have been almost homogeneous and relatively cool. But continued contraction of these materials caused them to heat, as did the radioactivity of some of the heavier elements. In the next stage of its formation, as the earth became hotter, it began melting under the influence of gravity. This caused the differentiation into crust, mantle, and core, with the lighter silicates moving up and outward to form the mantle and crust and the heavier elements, mainly iron and nickel, sinking downward toward the center of the earth to form the core. Meanwhile, by volcanic eruption, light, volatile gases and vapors continually escaped from the mantle and crust. Some of these, mainly carbon dioxide and nitrogen, were held by the earth's gravity and formed the primitive atmosphere, while water vapor condensed to form the world's first oceans.

Figure 5: The Earth's Center.

Research

Before we go any further, it is important to find out what is already known about the topic. You can research a topic by looking up books and magazines in the library, searching on the Internet, and even talking to people who are experts in the area. By learning about your topic, you'll be able to make thoughtful predictions.

Your experimental design might be influenced by what you have researched. Or you might even find that your question has been researched thoroughly. Although repeating experiments is valid and important in science, you may choose to introduce new ideas into your investigation, or you may change your initial question.

Terrestrial Magnetism

The phenomenon of terrestrial magnetism results from the fact that the entire earth behaves as an enormous magnet. The English physician and natural philosopher William Gilbert was the first to demonstrate this similarity in about 1600, although the effects of terrestrial magnetism had been utilized much earlier in primitive compasses.

Magnetic Poles

The magnetic poles of the earth do not correspond with the geographic poles of its axis. The north magnetic pole is presently located off the western coast of Bathurst Island, in the Canadian Northwest Territories, almost 1290 km (almost 800 mi) northwest of Hudson Bay. The south magnetic pole is presently situated at the edge of the Antarctic continent in Adélie Coast about 1930 km (about 1200 mi) northeast of Little America.

The position of the magnetic poles is not constant and shows an appreciable change from year to year. Variations in the magnetic field of the earth include secular variation, the change in the direction of the field caused by the shifting of the poles. This is a periodic variation that repeats itself after 960 years. A smaller annual variation also exists, as does a diurnal, or daily, variation that can be detected only by sensitive instruments.

Dynamo Theory:

Measurements of the secular variation show that the entire magnetic field has a tendency to drift westward at the rate of 19 to 24 km (12 to 15 mi) per year. Clearly the magnetism of the earth is the result of a dynamic rather than a passive condition, which would be the case if the iron core of the earth were solid and passively magnetized. Iron does not retain a permanent magnetism at temperatures above 540° C (1000° F), however, and the temperature at the center of the earth may be as high as 6650° C (12,000° F). The dynamo theory suggests that the iron core is liquid (except at the very center of the earth where the pressure solidifies the core), and that convection currents within the liquid core behave like the individual wires in a dynamo, thus setting up a gigantic magnetic field. The solid inner core rotates more slowly than the outer core, thus accounting for the secular westward drift. The irregular surface of the outer core may help to account for some of the more irregular changes in the field.

Inner Core Structure

Another theory that may explain some variations in the earth's magnetic field concerns the structure of the very inner core of the earth. In 1995 scientists at the Carnegie Institute of Washington announced that computer models of the earth's inner core appear to show one huge, remarkably aligned iron crystal. Scientists think that the atoms in the core are arranged so that each atom is packed with 12 neighboring atoms in a tightly packed hexagonal structure (see Crystal (mineral)). The molten outer core still provides the earth's magnetic field in this theory, but the inner core would have some effect, probably causing the magnetic field to warp slightly and causing especially large variations in the position of the magnetic poles during times when the outer core's effect is weaker, such as during a magnetic reversal. A crystalline inner core would also explain why shock waves caused by earthquakes take about four seconds longer to go from east to west through the earth than from north to south, because the waves would travel more quickly with the "grain" than across the grain of the crystal.

Field Intensity

The study of the intensity of the earth's magnetic field is valuable from the points of view of pure science and of engineering, and also for geological prospecting for mineral and energy resources. Intensity measurements are made with instruments called magnetometers, which determine the total intensity of the field and the intensities in the horizontal and vertical directions. The intensity of the magnetic field of the earth varies in different places on its surface. In the temperate zones it amounts to about 0.6 oersted (the oersted is a unit of measurement of a magnetic field; see Electrical Units), of which 0.2 oersted is in a horizontal direction.

Palaeomagnetism

Studies of ancient volcanic rocks show that as they cooled, they "froze" with their minerals oriented in the magnetic field existing at that time. Worldwide measurements of such mineral deposits show that through geological time the orientation of the magnetic field has shifted with respect to the continents. The north magnetic pole 500 million years ago, for example, lay south of Hawaii, and for the next 300 million years the magnetic equator lay across the United States. To account for this, geologists believe that the outer crust of the earth has gradually shifted around, even though the axis on which the earth spins has remained the same. If this were the case, the climatic belts would have remained the same, but the continents would have drifted slowly through different "paleolatitudes."

Magnetic Reversals

Recent studies of remnant (residual) magnetism in rocks and of magnetic anomalies on the floors of the oceans have shown that the magnetic field of the earth has reversed its polarity at least 170 times in the past 100 million years. Knowledge of these reversals, which can be dated from radioactive isotopes in the rocks, has had a great influence on theories of continental drift and the spreading of ocean floors.

Terrestrial Electricity

Three electrical systems generated in the earth and in the atmosphere by natural geophysical processes are known. One of them is in the atmosphere, and one is within the earth, flowing parallel to the surface of the earth. The third, which transfers an electric charge continuously between the atmosphere and the earth, flows vertically. See Electricity.

Atmospheric electricity, except for that associated with charges within a cloud and lightning, results from the ionization of the atmosphere by solar radiation and from the movement of clouds of ions carried by atmospheric tides (see Ion; Ionization). Atmospheric tides result from the gravitational attraction of the sun and the moon on the earth's atmosphere (see Gravitation; Tide), and, like the oceanic tides, they rise and fall daily. The ionization, and consequently the electrical conductivity, of the atmosphere close to the surface of the earth is low, but it increases rapidly with increasing altitude. Between 60 and 1000 km (40 to 600 mi) above Earth, the ionosphere forms an almost perfectly conducting spherical shell. The shell reflects radio signals back to earth and absorbs electromagnetic radiations approaching the earth from space. The ionization of the atmosphere varies greatly, not only with altitude but with the time of day and the latitude.

Earth Currents

Earth currents constitute a worldwide system of eight loops of electric current rather evenly distributed on both sides of the equator, plus a series of smaller loops near the poles. Although it has been contended that this system is induced entirely by the daily changes in atmospheric electricity (and this may be true for short-term variations), it is likely that the origins of the system are more complex. The core of the earth, which consists of molten iron and nickel, is capable of conducting electricity and can be likened to the armature of a huge electric generator. Thermal convection currents in the core are believed to move the molten metal in loop patterns relative to the magnetic field of the earth, producing the system of earth currents that mirror the pattern of convection currents within the core.

The Surface Charge of the Earth

The surface of the earth has a negative charge of electricity. Although the conductivity of air near the earth is small, air is not a perfect insulator, and the negative charge would drain off quickly if it were not being continuously replenished in some way.

In all places in which measurements have been made in fair weather, a flow of positive electricity has been observed to move downward from the atmosphere to the earth. The negative charge of the earth is the cause, attracting positive ions from the atmosphere to the earth. Although it has been suggested that this downward current may be balanced by upward positive currents in the polar regions, the preferred hypothesis today is that the negative charge is transferred to the earth during storms and that the downward flow of positive current during fair weather is balanced by a return flow of positive current from areas of the earth experiencing stormy weather. It has been proved that a negative charge is transferred to earth from thunderclouds, and the rate at which storms develop electric energy is sufficient to replenish the surface charge. In addition, the frequency of storms appears to be greatest during the time of day when the negative charge of the earth increases most rapidly.

The origin of the earth is not yet known. Because of this fact, it has resulted into many theories being put forward to explain its possible origin. But the most widely accepted theory is that, it was formed from a solar cloud made up of mostly hydrogen. On the religious point of view, it is believed that, the earth is a creation of God like any other living and non-living thing (s).