Plate Tectonic Theory

For several centuries it was believed that the continents were fixed permanently in their place. In 1965, an English scientist, Sir Edward Bullard using computer tested the fit of Africa and America and found that at a depth of 2000 meters the match was close indeed. It was then proved that continents are continually drifting away from each other on the surface of the earth like logs floating on water. This is called continental drift. Seabed is also recycled every 200 million years. Magma (molten rock) rises from inner layers of the earth at certain sites on ocean floor called ocean ridges.

The mid _Atlantic Ridge represents the boundary between two huge blocks of crystal material. The magma solidifies and moves outwards before being swallowed up at sites called ocean trenches. Thus new crust is being created by volcanic material welling up from below and spreading outwards. This process is called sea floor spreading and the boundary is called a constructive margin. These margins lie along ocean ridges. Since, the earth is not getting bigger this plates and are carried by their apart the continents. The edge of a plate where it is being destroyed is called destructive plate margin. These lie along ocean trenches.

Here, one block or plate or plate of crystal material is forced beneath another. This movement results in the earth quakes and volcanic activities. The idea of sea floor spreading combined with the idea of continental drift forms a theory what is called plate tectonics.

Earth natural satellite

The Moon is our only natural satellite. The young Earth had no moon, but soon after the Earth formed, a Mars-sized rogue planet struck it a huge glancing blow. A large chunk of Earth and most of the rogue planet were vaporized into a cloud that rose more than 22,000km in altitude, where it condensed gradually into the solid moon.Looking down from the north pole we would see the Moon orbiting counterclockwise from west to east. Neil Armstrong took that historical step of "one small step for man one giant step for mankind".The diameter of the moon is 2,160 miles. The Moon takes about 27 days, 7 hours, 43 minutes, 11.6 seconds to go all the way around the Earth and return to its starting position. The U.S.S.R. had made the opening gambit, sending the first artificial satellites into orbit, starting with the 83.5-kilogram Sputnik I in October 1957. Most planets are named for Roman gods but moons are named for Greek gods.The moon is slowly moving away from Earth. The current distance between the Earth and the moon is 384,000km but it was closer in the past.

Comet

Earth mostly regarded the comets as messengers of destruction and rarely as bringers of good or prosperity, while the scientists today think they might have played a key role in the formation of our planet and view them as carriers of possible information about the galaxy. Comets have been the most feared and admired sky spectacles of all. But while astronomers have been able to predict eclipses for thousands of years, only in the 1700s was a comet's return correctly predicted, by Edmond Halley. The comets that pass close to the Sun originally came from one of two places that either the Oort cloud or the Kuiper Belt. You can think of the Oort cloud as a giant spherical shell surrounding the Sun that's filled with about 1 million comets. In the early 1930 an Estonian astronomer proposed a structure formed of billions of comets which lie beyond the Kuiper belt. However, the theoretical structure one light year in radius equivalent to a quarter of the distance to the nearest star to the Sun, Proxima Centauri, has not been detected yet.

Apollo 11

Apollo 11 was scheduled to fulfill an age-old dream of mankind. July 16,1969, Was the fateful day when the Saturn V rocket carrying Apollo 11 rose gracefully into the air from cape Canaveral. Its crew whose names were to go down in history, Were all experienced astronauts from the Gemini programmed- Neil Armstrong, Michael Collins and Edwin Aldrin. Their launch and outward voyage to the Moon proved faultless, a good omen for their later success.

The Apollo flight plan required a space craft made up of three sections or modules. The three-man crew were housed in the command module (CM) linked to the main equipment section, the service module (SM). For the outward fight the CM was mated to the lunar module (SM). For the outward fight the CM was mated to

The lunar module (LM) when the craft reached Lamar orbit. Armstrong and Aldrin crawled into the LM nicknamed Eagle and separated it from the CM for the descent to the selected landing spot in the sea of tranquility one of the Moons land plains After their moon walk, they returned to dock with the CM orbiting above the LM was then discarded before the flight home.

Sun

The sun is just one of about 100 billion stars in our galaxy. The Sun is by far the largest object in the solar system. It contains more than 99.8% of the total mass of the Solar System. The Sun's diameter is around 1.4 million km. It is approximately 109 times wider than the earth. The diameter of the Sun is 840,000 miles which is more than 100 times the diameter of the Earth. Its mass is more than 300,000 times that of the Earth with a surface temperature of about 5500° C. The outer layers of the Sun exhibit differential rotation at the equator the surface rotates once every 25.4 days and near the poles it's as much as 36 days. The Sun is about 4.5 BILLION YEARS old. It will probably continue to exist in its present FORM for about another 5 BILLION YEARS before RUNNING out of HYDROGEN. Astronomers think that the Sun formed from the solar nebula about 4.59 billion years ago. The Sun is in the main sequence stage right now, slowly using up its hydrogen fuel.

First Astronaut

Like the first satellite, the first human to travel in space was a Russian. His name was Yuri Gagarin. An army major, the 27 – year – old Gagarin blasted off from the Soviet Union in his Vostck I space – craft on April 12, 1961. The overstock I was a sphere 2.3 meters (7.5 fit) in diameter coated with heat – resistant material.

A small instrument unit behind the sphere jettisoned (cast off) before re – entry contained gas bottles to provide air for the consonants as well as electrical batteries and retro rockets. Before – entries the atmosphere overstock 1 high. Gagarin was ejected from the spacecraft after re entry and he parachuted safely to the earth. Bigger chutes opened on Vostok I carryings the space craft to a gentle landing. From blast – off to loading Gagarin’s mission lasted 108 minutes.

Earthquake

An earthquake is a series of vibrations on the earth's surface caused by the generation of seismic waves due to sudden rupture within the earth during release of accumulated strain energy. Most recent seismic codes include response modification factors in the definition of the equivalent lateral forces that are used for the design of earthquake resistant buildings. The crust of the earth when it is subject to tectonic forces, bends slightly. But, because the crust is rigid, when the stress or pressure exceeds the strength of the rocks, the crust breaks and snaps into a new position. The effects of earthquakes vary. This is a result of a variety of factors such as the strength of the earthquake, the level of population in an area and the level of economic development of the area struck. Earthquakes cause thousands of deaths worldwide every year, and systematic study of the causes of these deaths can lead to their prevention. Few studies have examined how multiple types of risk factors are related to physical injury during an earthquake.