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What is life?
Question Date: 2015-04-06
Answer 1:

It’s actually pretty hard to have a good definition of life that everyone will agree on. One wrong definition that might make sense is a system that can grow spontaneously, but crystals can do this and they aren’t alive. Another incomplete definition would be a system that uses energy to make more of itself, but fire does this and is not living. The big difference between living things and fire is that living things transfer information from parent to child whereas fire does not. A child of a living thing is very similar to the parent of the living thing which is generally not true in things we wouldn’t consider alive. So life can be considered to be a system that uses energy to make similar or identical copies of itself. Living things do this through DNA which contains the information that is passed down from parent to child. Though there are different definitions of what life is and sometimes something like a virus may not be considered to be alive even though it has a lot of the same behavior of living things. As a scientist, you need to have a strict definition of life, but the truth is that it’s really difficult to say what exactly life is. We know what living things tend to do and abilities most living things share, but pointing to one thing that would let you know something is life is actually really difficult.

Answer 2:

We don't have an exact definition between life and nonliving things. There is nothing on Earth that isn't clearly one or the other.

To the best that we can say, life is a complex chemical reaction that carries information from parent to offspring. The chemical ways that make rocks and minerals can do this, though, but they aren't nearly as complex. What will happen when we encounter a chemical reaction that is less complicated than life as we know it yet more complicated than rocks is something we'll have to see when we encounter it.

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