"We know that Mars once had liquid substances flowing over its surface, but why do we think it was water? Could it not have been something else?"
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Question
How numerous are bacteria on Earth at any given time?
In terms of numbers, bacteria are by far the most numerous of organisms on Earth. They also make up most of the living biomass on Earth. Unfortunately, I'm unaware of any actual estimate of the number of bacterial cells on Earth. In fact, we don't even have a very good estimate of the number of different species of bacteria. What we do know is that there are over 1000 species of bacteria living inside of us, with 300 species of bacteria in a person's mouth alone, and that we have 10 times as many bacterial cells as blood cells in our bodies. Answered by Prof. Lee Kump
May 1, 2002
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