What Is Life? (astrobiology approach)
It seems obvious when something is alive. But it turns out that the answer to this question is not quite as obvious as it seems. We might wonder why we would even want to ask that question.
So let's have a look at some of the characteristics that define living things:
1. life is complex and exhibits complex behaviours
2. life grows
3. life replicate (divides)
4. life metabolizes (eats food) and makes energy
5. life contains a system for storing information
6. life evolves by Darwinian (or artificial!) selection
It is important to remember that each characteristic we can apply for non-living things.
1. tornado exhibits complex behaviors
2. crystals grows
3. virus cannot replicate, but computer program can
4. fire metabolize
5. computer store information
6. computer programs can evolve
Here is a definition by Gerald Joyce, a NASA scientist, who described in 1994 life as, a "self-sustaining chemical system capable of undergoing Darwinian evolution."
Just one example of a type of written definition.
And what definition of life do you like most?
Please, share in comments.
I want to share two best online courses about life:
Introduction to Biology - The Secret of Life. Professor Eric Lander and the MITx Biology
--Anna
I think the issue with the non living things that exhibit life-like behaviors is that each thing exhibits only 1. Life exhibits all. Viruses need a host to replicate, but then so do many intestinal worms.
I like the "life exhibits ability to evolve." Sure, there are organisms that have been largely the same for millions of years (turtles, for instance). Bacteria have been around since the beginning. But that just means that certain organisms are adapted to be stable over time.
I look up at the sky at night and sense life, an energy beyond the physical. Is the Universe alive too?
love this quote
"We are a way for the cosmos to know itself.”
― Carl Sagan