Sample Multi-paragraph Essay

       Throughout human history, the physical universe has often presented dangers to explorers. For example, when primitive humans left their tribal villages to search for food and water, they risked death or injury from dangerous animals. Later, when people sailed the oceans in search of new lands for settlement or trade, many died in terrible storms. Similarly, the ocean of outer space has many dangers, but it also has several unique challenges for explorers.
       One of the challenges that are unique to space is the fact that space is a vacuum, which is a risk for various reasons. First, in a vacuum there is no atmosphere and therefore no air pressure. Without air pressure, the human body has no oxygen to sustain itself. After too many minutes without oxygen, a person would lose consciousness and eventually die. Also, in a vacuum a person's blood will gradually begin to boil. Finally, without an atmosphere, the rays of the Sun can cause radiation poisoning.
       Another difficulty that is unique to outer space is the presence of meteors and micrometeors. These are pieces of rock and metal that are left over from the formation of the solar system. Many of these objects travel at very high speeds. Under the Earth's blanket of air, people are usually protected from metor impacts. However, in space, people and spaceships are vulnerable to collisions with meteors. It is true that the chance of metor impacts is relatively small, but if even a small micrometeor happens to collide with a spacecraft, it could cause serious damage. 
       A third special challenge involved with the environment of space involves the fact that it is very difficult to find life-sustaining water off the Earth. For example, the planet Mercury, which is closest to the Sun, is too hot to have water, so space travelers must take water from Earth if they want to visit Mercury. A similar situation exists on the planet Venus, second from the Sun. This planet is likewise too hot for water to exist. Similarly, the fourth planet, Mars, is too cold and dry, although there may be some water frozen at the north and south poles of the planet.
       There are other difficulties involved with space exploration, but these are three of the most important ones. In summary, without adequate air pressure, the unprotected human body may be seriously harmed in a vacuum. In addition, meteors can threaten human life and damage spacecraft. Finally, the lack of water in space means that human life may have a difficult time surviving on other planets. As one can see, the challenges of space travel are rather different from terrestrial dangers. 

View of Earth from lunar orbit, December 1968,
as seen from the Apollo 8 spacecraft.
Photo courtesy NASA

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