How is "life" objectively defined?
There is a scientific border between life and non-life as you say. From a historical point of view we first separated things to organics and non-organics up until 1828 that a scientist, Wohler, made an organic compound called urea from some inorganic compounds. And today we know that all organic compounds are made up of inorganic ones. But your question is a bit harder to answer because the definition of life is not that obvious. If life means living organic things then there is still a way to separate a live organic stuff from a dead one by their physical/thermodynamical state.
From the simplest organic compound, urea, to the most sophisticated organ on the planet earth, human brain, there are different borders that can also be considered as the border between life and non-life, for example some biologists believe that viruses are the smallest living things because they can reproduce and conserve their RNA, most others believe that biological cells like bacteria are the first living things due to the reproduction of the whole cell using their DNA. There are also other borders, for example living things are energy/mass consuming they must be constantly fed. What ever you chose to be the border you'll find out that it's not something special and you could have chosen another border. It's not an objective border, it's just a definitive border.
There are a host of potential criteria which have been suggested and the potential exceptions to each putative criteria make this a somewhat difficult question to answer unambiguously. Nevertheless the most plausible candidates are
- Living things do or have the potential to undergo the process of darwinian evolution
- Living Things are information processing 'machines' (if you will) whose causal capacities and downstream behavior are dependent both on stored prior information (DNA) and to the experiences manifest in their respective lives
- Living things are uniquely intentional homogeneous forms of matter which have the capacity for (some form of) representation, by which novel causal (possibilities) are made actual.
Though there are many others, the most plausible involve information retaining and modifying capacity, which imply the possibility of alternative histories depending on the set of actualities which occur. These are dependent on the information processing mechanisms made possible by the existence and function of DNA and correlated gene expression, which are causally necessitated by the organism being involved in evolutionary processes.
When I was at school, which was a long time ago and so things may have changed somewhat, we were taught that living organisms exhibit a number of properties:
- they move
- they reproduce
- They make new cytoplasm
- They respire
- They respond to stimuli And probably one or two others. This still more or less holds up since self-replicating machines are still rather limited. However, this definition tells us how to identify a living organism rather than telling us what life is. It would be fair to say that life is a property of living organisms rather than a thing in itself and so you could argue that it doesn’t exist depending on your definition of ‘exist’. By such a definition you would probably also say that other properties such as size, weight and time don’t exist, which seems counterintuitive to me but of course a word can mean anything that we agree it means.
Nonliving chemical processes don't try anything. When they run out of resources, they simply stop.
Living beings try to keep on living. They do whatever they can to keep on going:
- They try actions to collect more resources (energy and building blocks)
- They try to use the resources to maintain and improve their own ability to collect and use resources
- They try to multiply to keep the species alive despite the eventual death of the individual.
Here is Dr Jeremy Sherman describing the difference between living and dead: