From a cosmic, observational and documentary perspective, 'life' is an autophageous existential phenomenon of multiple individual 'biochemical' entities, which replicate by means of molecular machines, and which progressively complexify by evolving into interacting groups, in response to the influences of the environment, scavenging and predation.
The main characteristics which seem in evidence... as we attempt to comprehend what it is that we are a part of... is that life consists of entities that reproduce themselves, that have characteristic time-intervals of existence, that provide their own molecular materials for recycling, that undergo incremental change, and that form groups and sub-groups of interacting individuals.
At the present phase of its evolution, it thinks is has become self-aware, able to investigate itself, and to reflect about its own nature.
Although at some scales and circumstances, evolutionary change proceeds at a rate that we can observe and understand... in animal and plant breeding and microbial research for example... now that we are aware of all the fossil evidence, we are compelled to attempt to come to terms with the incomprehensible intervals of time that must have elapsed, for many of the changes to have taken place.
Within the universe of stars, galaxies, planets, comets, molecules, etc, etc... the observation that all phenomena are represented by innumerable examples, would suggest that the phenonena of 'life' in particular, is no more likely to be unique that any other.

From an introspective anthropocentric viewpoint, 'life' is a fleeting chance to avoid being eaten, promote propagation, and then be reabsorbed. Survival relies upon effective simplifications, and every living thing must have a strategy for enforming complexity, or being re-digested by nature. Life is a chaotic game where at the core biological level, the ruthless rules pay no deference whatsoever to human aspirations of fairness, and winning and losing is played for keeps. It is a brief opportunity for an organism to play that small part in the game for which it has the ability to manipulate the constraints. Earthworms can cope with many of the rules of life in the soil, but not the circumstances existing in the full light of day. Ferns enjoy the conditions of forest damp, but cannot cope with the rules of desert water availability. However much one might like bows and arrows, it is difficult to be an armless archer. At physical levels such an observation is blindingly obvious, but at social and cultural levels, individuals can have ludicrous and unrealistic expectations of participating in certain parts of the game without appreciating the rules there. To participate in sex, one must learn and successfully play the local rules. To become rich, one must learn the financial constraints and how to circumvent them. To become an actor, or a politician, or a comedian, one must learn how to deceive the rules of expectation.

The life of an individual is constrained by certain core realities. It is a participant in an evolutionary complexification process, whereby replicating object sequences accumulate the capacity to store information about the past, use that information to modify interactions with the rest of existence, propagate an improvement, and then be re-consumed. It has no existence outside of this transient participation process. An individual life is a progressively unsustainable struggle to keep its set of inter-related system parameters within comfortable limits. The biological demands of respiration, digestion and temperature control... the physical demands for shelter, food acquisition, medical care and sex... the social demands of customs, taxes, war and politics... are all interacting systems which the individual must keep in equilibrium for continued survival.

Opportunities arise during most lives for apparent choices to be made. Many humans seem unable to make these choices themselves, and need to rely on an imposed religious simplification. An atheist option however, when wishing to choose what to do with one's life in order to attain happiness or fulfilment could perhaps be resolved by deciding to what extent one identifies with one's self or the wider nature. Identify with the cosmos, and any intrinsically creative enterprise which appeals to the imagination could be a satisfying life-choice. Identify with the one's self, and any number of acquisition alternatives might become readily available. It is not practical however, to choose one extreme to the exclusion of the other. Balancing a commitment between self and not-self is in fact a pragmatic existential necessity. The egoist can no more absolutely ignore nature, than the altruist can ignore their individuality.

For most individuals the social circumstances of their life demand that they conform. If the local rules are religious and political and intransigent, then participating demands that they are adhered to. Unless an individual can link up with a substantial support system, revolting against the status quo involves victimization, banishment or death. In many societies, individuals have a very restricted choice as to what to do with their life.