AST 309 Chapter 7: Chapter Seven Notes
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The age of these surfaces is not necessarily the age of the planet as a whole. Geologically active objects can have planet weathering which erases evidence of earlier epochs and presents us with only a relative young surface for investigation. Works because the rate at which impacts have occurred in the solar system has been roughly constant for several billion years. So, the number of craters is proportional to the length of time the surface has been exposed. Crater counts can only tell us the time since the surface experienced a major change that could modify or erase preexisting craters. Half-life: a specific time period during which the chances are fifty0fifty that decay will occur for any of the nuclei. Radioactive elements with half-lives we have determined can provide accurate nuclear clocks. The decay of radioactive nuclei generally releases energy in the form of heat.