What does it mean? There's a movie by this name, and i've heard people saying it often. I have been trying to find its answer but couldn't find any. A sentence/example would be nice too.
Life in the way which we see/understand it. Or more commonly, as it currently is.
The sentence is suggesting that we do not currently understand something entirely, but have a certain level of understanding. It is giving the context of "life" as it is currently understood. There may be other forms of life we can't even comprehend, or have just never seen. Similarly the concept of life may change over time. Consider bacteria, which is a form of life we simply didn't know about 500 years ago.
A more elaborate example.
Life, as we know it, is hard. Maybe one day, humanity will find a way to make it easier.
The implication is that life may one day become easier, but right now (the way we understand it) it isn't. Alternatively it may have previously been harder
Life as we know it is easy, imagine working in a coal mine 200 years ago!
Again this sentence is using "as we know it" to give the context of "as it is now"
From Google Books:
Scientists may speculate about life on other planets and in other solar systems, but at present there is no proof of life, as we know it, elsewhere in the universe.
The meaning is: we know our kind of life - carbon-based, liquid water-dependent, using RNA- and DNA-based mechanisms for self-replication.
On other planets, life might exist in other configurations, not as we know it, and hence be hard to detect, for instance. All we know at the moment is that we see no traces of life as we know it on other planets.
In a way, viruses might be considered aliens, because they are so different from the life as we know it that is cellular life.
Life as we know it is cellular. Viruses are not cellular. They have no cell membrane. Yet they have genetic code and are able to propagate themselves via replication quite effectively. If viruses are alive, it's not life as we know it.
Both answers are correct. We know, thus far, only earth life, life which has DNA and RNA as coding mechanism for the organism to grow, walk, replicate or do other specific activities during its life. This life is composed of atoms, ninety-two elements, which exist in all universe as matter. When scientists state "life as we know it" they simple say that for something that might be outside of our current recognition and knowledge. It could silicon-based life, or liquid-based, or it is only steam-constructed "life". Scientists thus try to stay neutral to life definition—by not being influenced by life, like we are.