If I had a microscope that could see atoms and molecules, how far out would I need to zoom before I could tell I was looking at life?
I’ve heard things like “people are 70% water” but water is not alive.
I’m asking in chemistry because I’m not sure if life at a molecular level is considered biology.
In: Chemistry
**Tldr**: Life is an emergent property above the molecular level. You need a number of complex molecules working together to create it.
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“Life” as we generally understand it only exists a level higher. There is nothing at the molecular level that has all the hallmarks of life, one of the definitions being “any system capable of performing functions such as eating, metabolizing, excreting, breathing, moving, growing, reproducing, and responding to external stimuli”. Though, *exact* definitions vary.
You can mix some molecules together however, and start reaching these qualities, but that hits the field of microbiology, cell biology (my field), and so on. You see, life is an emergent property–a quality or characteristic that can only exist as a *greater than the sum of its parts* arrangement. If you continuously break it down, eventually it no longer exists among its separate parts.
One of the classic transition points of life (because it’s frequently debated on whether or not it is alive) are viruses. Viruses are, essentially, DNA/RNA packaged by a handful of proteins, that code for little else except the machinery to make more DNA/RNA and proteins to make more viruses. That’s it. And this strand can be as short as only a few thousand base pairs, as opposed to human genomes’ billions of base pairs. Viruses lack some of the criteria of life, but replicate themselves *using* their hosts, as if they were a tag-along that achieve qualities of life largely by borrowing them.
Go further up from here, and you have cells which we all agree *are* alive. Go below, and you have individual molecules which we do not consider alive, despite having activities that when put together start becoming life.
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