5 Asteroids in Direction to Earth And Its Date Of Collision.
Impact Cratering Dating. Nathan Marsh. Relative Dating. Simple but not as informative; Measures the crater densities (craters per square kilometer); Generally a. Crater counting is a method for estimating the age of a planet's surface. The method is based method has been calibrated using the ages obtained by radiometric dating of samples returned from the Moon by the Luna and Apollo missions.
For the other planets, like Mars, we will be unable to apply radiometric dating until we can study rocks from their surfaces in a laboratory. Since the first feature of those photographs one sees are the very large numbers of craters, one asks "what use can we make of craters to determine something about the Martian surface? The largest bodies the ones that would form the largest craters were used up before the smaller ones, since there were fewer of the larger ones to start with.
We can roughly divide the history of crater dating craters into three periods, from oldest to newest: large and small craters formed small craters only formed very few craters formed Since the planets were formed by the datings craters of objects, we would expect all of the planets to be uniformly covered with both large and small craters.
However, if we take a map of Mars and plot every crater of diameter km or greaterwe get this: So craters are not uniformly distributed on Mars; instead, there are a few areas with significant numbers of very large craters greater than km in diametermost of the rest of the southern highlands have only smaller craters, and all of the northern lowlands have very few craters.
We can color-code these regions, using red for the most heavily-cratered areas the areas with the largest cratersgreen for the intermediate areas, and blue for the least-cratered areas. Since no one can think of a process that would erase only large craters, there must be something that erases all craters and "resets" the surface to smoothness.
This process was probably volcanic in nature: through time, lava flows buried all of the craters in some areas.
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