The mississippi river is a physical feature as it was discovered during a time where man weren`t capable of such construction in the earth.
Answer: 3.6 seconds
Explanation: Geologic time is a way of measuring time based on events in the history of the Earth. If we compress this into one year, a single geologic year equals 4.6 billion years because the planet was formed 4.6 billion years ago.
Columbus arrived in the New World in August 1492, 528 years ago.
If 4.6 billion years = 1 year in geologic time,
528 years = 528 X 
=3.6 seconds
<em>(I broke the year down into seconds by breaking it down into days, then hours, minutes and seconds because the value is very small)</em>
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<em>So, if we compress geologic time into a single year, only 3.6 seconds have elapsed since Columbus arrived in the New World</em>
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They show that there was an ocean over the plains long ago, and fossils are always used to elaborate on the history of life/how it developed.
E. indoor plumbing
because this comes in agriculture wich hellped southeast development