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Meteorites
The far reaches of space are known for various stars, planets and moons, but one often overlooked celestial bodies are meteorites. Meteorites can either consist primarily of stone, primarily of iron and nickel or a mixture of both and can vary greatly in size. A meteorite is characterized by its ability to enter the Earth's atmosphere and find its way to the Earth's surface. It is only upon entering the Earth's atmosphere that a meteorite is actually categorized as a meteorite; prior to this event they are known as meteoroids. Meteorites usually began as either parts of an asteroid or a comet. There are several hundred known asteroids that orbit around our solar system and the vast majority of meteorites come from these bodies of rock and metal. A meteorite that comes from a comet is far less common. These meteorites are the icy, rocky fragments that come from a comets head or tail. Though it may seem like the planet has been hit by very few meteorites in our lifetime, meteorites are a surprisingly common occurrence. While the average person may not notice, an average of 100 tons of meteorites hit the Earth's surface on a daily basis. Being the size of small pebbles and other inconsequential sizes, most of these meteorites go completely unnoticed as they hit various land and water formations.
Throughout the history of the Earth, the surface has been hit by many large meteorites. It is theorized that about ever few hundred thousand years a meteorite larger than a mile hits the earth and that every 10 million years the Earth is hit by a meteorite up to six miles in diameter. As of today, there are about 160 recognized impact craters on the Earth's surface. This number does not represent the true presence of meteorites though, because most fall into the ocean where evidence is quickly washed away. There are several famous craters found across the world, which give a look into the Earth's historical encounters with meteorites. The Vredefort Crater in South Africa is one of the oldest and largest known craters and dates back to nearly 2 billion years ago. The world's largest known crater is found in Ontario, Canada and measures a whopping 155 miles in diameter. In 1991 one of the most important meteorite discoveries was made. A massive crater, which ranged in size from 110-180 miles in length was discovered in Mexico. It must be noted that, when a meteorite hits the Earth surface, its crater is twelve to twenty times its actual size. With this information known, it was concluded that the meteorite that created the indentation in Mexico was at least a mile in diameter. The impact from such a large mass was one of the most destructive forces in our planets history. Scientists widely accept the theory that it was in fact, a meteorite that created this crater and the event marked the extinction of the dinosaurs.
Some may wonder how a meteorite could be responsible for the entire extinction of a species; the answer is, more easily than one would hope. The impact of a large meteorite has the potential to affect the Earth for thousands of years. The initial impact would create dust and debris that would not only pollute the Earth's atmosphere, but would also cause forest fires. The airborne debris, coupled with the soot and smoke from the fires would create a cloud capable of sending the entire world into darkness. The darkness would have the most noticeable effects on the Earth's population. First, it would lead to the death of plants and vegetation, which need sunlight to carry out life. Secondly, the darkness would block the sun's heat from entering the atmosphere, casting the planet into intensely low temperatures. In short, a meteorite has the ability to complete hinder all process that sustain life. Humans are not above the dangers of meteorites and it is for this reason than an extensive amount of funding is placed towards watching the skies for the impending doom of a large, earth-bound asteroid or other large rock formation.
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