MadSci Network: Earth Sciences |
Earth certainly is bombarded by a large amount of material from outer space. This material can come in all different sizes, from the largest meteorites and comets to the smallest grains of dust. In general, the odds of a large meteorite hitting the Earth are extremely small. A meteorite the size of the one that killed the dinosaurs will only fall to Earth every 100 million years or so. And most meteorites that start out larger in outer space (10’s of tons or smaller) will be broken up as they pass through the Earth’s atmosphere, so that when they reach the surface they won’t do too much damage. Therefore, although there is big stuff that occasionally falls to Earth, this is not the main source of cosmic debris. Rather, the material that we sweep up every day from outer space is most likely to be extremely small, sand grain size or smaller dust. At night, when you watch a meteor shower and there are many streaks of light passing across the sky, you are actually watching sand grains burn up in our atmosphere. The friction from the atmosphere rubbing on the sand grain as it moves very quickly is hot enough to burn that sand grain up and we see the heat as a meteor. The Earth captures about 40,000 tons of dust from outer space each year (so you can see that the big stuff is hardly important compared to all the little stuff). These dust particles are usually very rich in carbon and otherwise contain tiny bits of minerals that are commonly found in meteorites. Billions of years ago, when the solar system was still very young, there was a lot more material floating around in our solar system that could be swept up onto the Earth and so the numbers above would have been much higher nearer the beginning of the solar system. Back then, it might have been possible for an extremely large impact to affect the Earth’s rotation or length of day. And, of course, a very large impact, like the one that led to the extinction of the dinosaurs, can have huge and global effects on life on Earth. However, even the meteorite that caused the dinosaur’s extinction was not big enough to affect the Earth’s gravity, rotation or length of year. For more information on the cosmic dust that falls to Earth, technically termed "Interplanetary Dust Particles" or IDPs, check out this website from Washington University in St. Louis. There are some great images of what these particles look like: http:// stardust.wustl.edu/IDPIntro.html
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