Where Chemistry Stops and Biology Begins

The first question of Astrobiology is "How did life begin and develop?". In order to answer this question, we need a working definition of what exactly we will consider to be "life". Life is very hard to define exclusively; any definition you come up with will have a counter- example to go against it. But, in order to determine how a collection of molecules becomes life, or where chemistry stops and biology begins, we onlyneed a definition of life that is true at the molecular level. It doesn't matter to us if a large organism such as a mule goes against our definition as the problem we are looking at is specifically defined at a much smaller scale.

Under these conditions, from a biochemistry viewpoint, life can be defined as:

"The ability of a system to maintain itself in a state far from equilibrium, grow, and multiply, with the help of a continual flux of energy and matter supplied by the environment" (de Duve, 4).

Anything meeting this definition will be able to: 1) make its own parts from molecules in the surrounding environment, 2) take energy from its environment and use it to do the work necessary to stay alive, 3) catalyze the reactions needed to live, 4) store the information that will enable it to reproduce accurately, 5) control any exchange (of nutrients, wastes, etc.) with the outside environment, 6) modulate activities so that organization is preserved during a change in the environment, and 7) multiply (de Duve, 4)

Using this working definition we will be better able to approach the complex problem of determining how life came to be on Earth.