How do we know if things are alive?

[talikhan]

How do we know if things are alive

[Haitch]

We can't. There are certain things we understand such as respiration that identify a great deal of things to be alive but there is no clear definition. One is being worked on at the moment otherwise the current Mars missions could end up being a waste of time and money if we can't actually tell if they've found life.

[rekstout]

In GCSE biology I was taught that to be defined as alive, something had to exhibit a series of behaviours. The acronym RINGMER was used as a mnemonic, unfortunately, in my youthful zeal to undo the damage formal education did to me, I have forgotten most of them - Reproduction, Ingestion, N?, Growth, Movement, Excretion, Reaction - maybe. The acronym was specific to my Biology teacher as she was from near the town Ringmer.

[beenee]

I heard that Nitrogen was the base of all life on earth.