Part C
Impact!
Meteorites all have one thing in common: they reach the surface. The fall of some meteorites is slowed by the atmosphere so much that they are reduced to free-fall velocity and cause little or no impact damage. However, larger or more dense meteorites typically form craters. What happens during impact and how are craters formed? Where are these impact sites located on Earth? Let's find out.
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Figure 5-6. Impact craters on Earth and on the Moon. At left is Wolfe Creek crater in western Australia. This crater is 0.875 km wide and was formed about 300,000 years ago. At right is the lunar crater Copernicus, imaged by Lunar Reconnaissance Orbiter. Note the prominent central peaks, stairlike terraced walls descending to a flat floor, and a rough surrounding ejecta blanket. Copernicus crater is 93 km across, over a hundred times larger than the Wolfe Creek crater. |
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Impact Processes & Features
The impact of meteorites on a planetary surface is a highly dynamic event. Although these phenomena are rarely witnessed, the processes can be largely reproduced and modeled so we can have a better understanding of what happens during an impact event.
The impact process can be described as having three distinct stages:
1) initial contact and compression
2) excavation
3) modification and collapse
Let's use the Wikipedia's Impact crater web page to review impact processes and features and then answer the following questions. Read the relevant section and before answering each question.
Terrestrial Impact Craters
If you want to know where impacts have occurred on our planet, the most authoritative source for information is the Earth Impact Database. Data for the 170+ confirmed impact locations is summarized on the Wikipedia's List of Impact Craters on Earth web page. Refer to this web page to answer Quiz Me! questions C40 through C44.
You can also click on the "Coordinates" link for each crater to see imagery of the crater location. Cool!