What is the difference between a meteor and a meteorite? According to Webster's dictionary a meteor that reaches the surface of the earth without being completely vaporized is a meteorite. Meteors have been hitting the Earth, planets, moons and sun since the beginning of time. Some have made it to the surface of the Earth without being completely destroyed. These we call meteorites. When we look up at our moon, we can see the various craters, many of which were caused by impacts. If our Earth was not a living planet with oceans and plant life, it would probably show as many craters as the moon. Since the Earth is 4/5ths water, we have to assume that most of the impacts have occurred there. Even the ones that made it to land and caused a large crater, have been erased by time. There are a few visible from space, but the bulk of the craters have been eroded or covered with plant life or are under the water.

A meteor is sometimes called a shooting star as it lights up in the Earth's atmosphere before it is completely burned up. When a meteorite makes it to Earth it is called a fall. When scientists go out and find one, that is called of all things, a find. When scientists name meteorites, they name them for where they are found. That is usually a nearby village or town etc. or a landmark of some kind. If a meteorite fell down near a town named Axis, it would be named the Axis Meteorite. There are three broad categories of meteorites:
1. Stony
2. Iron
3. Stony/Iron

I guess everyone knows that a meteorite was accused of wiping out the dinosaurs. While most scientists think that this was a tragedy, I say it was a lucky hit. We may not have been here if it wasn't for that hit. If you believe that man evolved into what he is now, how would early man have survived with predatory dinosaurs after him? The impact is believed to have taken place at Chicxulub, Mexico and a huge crater is there that is buried under sediment. The impact is estimated to have been 2,000,000 more times powerful than the most powerful nuclear device ever tested. This device was known as the Emperor bomb which had a yield of 1/20 of a gigaton. Incredible tsunamis must have been formed along with dust and dirt blowing up into the atmosphere. The crater formed by this hit is about 170 km or about 102 miles across. Mexico was not the only place hit by huge meteorites. There may have been two other locations that were just as big or even bigger. These two are the Sudbury Meteorite in Canada and the Vredefort Structure in South Africa. These two are yet to be measured precisely.

Another huge crater exists in Acraman, Australia. It is 160km across or about 96 miles in diameter. There is some disagreement about the diameter of the crater. It is said to have been formed about 590 million years ago This crater was also preserved by marine sediments. This meteorite was not actually being looked for when the crater was discovered. As a matter of fact this is the first time a meteorite impact has been directly linked to the debris. It turns out that scientists were actually there only to date volcanic rocks. Prior to this find it was thought that the crater might have been formed by volcanic eruptions. This theory doesn't seem to be the prevalent one any more since most of the evidence now points against it.

One of the most visible craters is in Crater Lake National Park. The lake was originally formed not by a meteorite, but a volcanic eruption. It is impossible to tell the origin of some of these craters. Sometimes the ones formed by meteorites and the volcanic ones look the same. Another very visible crater is the Barringer Meteor Crater in Arizona. This crater was caused by an impact and is .737 miles in diameter. It is a very young crater in geological terms being under 50,000 years in age. The best guess is that it is about 49,000 years old. For quite some time there was much disagreement on how the crater was formed, but fragments of the body that hit it have been found.

Crater At Manicouagan, Quebec, Canada
Photo Source: NASA

Another large impact crater is visible by air at Manicouagan, Quebec, Canada. This is definitely an impact crater and is about 62 miles across. There are many different estimates of the crater's age and they can vary as much as one million years. There are only a few well preserved craters of this size that are clearly visible and this is one of them. A lake partially fills this crater. Some of the rocks inside the crater have been eroded by glaciation. The rim of the crater has been worn down but there is enough evidence left to estimate its size.

There is an impact crater that is located in Gosses Bluff in the Northern Territory of Australia. It is not huge, being only 24km or about 14.5 miles across. This is still pretty big to me. What I think makes this impact crater unique is the fact that some scientists think that it could have been made by a comet or meteorite. It resembles a bull's eye with an inner crater structure. The crater has been subject to much erosion and this is another one of those craters where the time of the impact varies as much as 1/2 millions years by the experts. The outer crater rim is eroded, but there is enough of an impression left to see where it was.

There is no doubt about it, our Earth is some sort of cosmic target, but we are protected by our thick atmosphere from all of those little hits that occur every day, otherwise we would look like those characters in the old cowboy movies that were made to dance while bad guys shot at their feet. We would be dancing to avoid all those small particles. Ouch! Those big boys only hit us on the average of about once in 10,000 years and as technology advances, we may be able to prevent this too.