I suppose the key to understanding these types of questions (Harrumph perhaps comes the closest) is to realise life as a system of interdependencies between what we as humans sometimes falsely view as separate organic entities/states.
When I ask what would we call, can also be easily be read as; what position with in such a system of interedependent organic entities and states, would we assign to the entity/state that can realise the systems (hence also its own) contingency, and also realise and imagine the actions that could extend the systems existence beyond the life span of the planet, in our case the planet earth.
My use of the term purpose in this context is a little regrettable and I could refer you to the ideas of the great minds. But I prefer to engage with resource to expanding upon what I mean by the term in the context I use it here. Again, this term interdependency perhaps best illustrates my use and perhaps even binding it with a second term to form ‘functional interdependencies’ illuminates my use further for you.
When I am talking about the time required for a life system on a planet to evolve an entity/state capable of such realisations and potential capacity to make provision for such a systems continuance beyond, for want of a better term, ‘home planet’, this is from the point of view of what we know about evolution.
For example, for the planet earth humans are perhaps the only entity/state that is capable of such realisations and we can talk about, with reasonable levels of probability, the time taken for us to have evolved from decreasingly less complex entities/states. Note that this would be a series of time slices as it depends on where we first decide to locate where and what we have evolved from. So, the important numbers to tease out in the context of these questions, is comparing the natural life span of a life bearing planet (dependent upon external events and the life cycle of stars) and the time taken for the system of life on that planet to evolve an entity/state to realise the above points.
On a final note and returning to this term purpose (which I found grammar inclined me to use) and to pick up upon Harrumph’s comment regarding god i.e. prime mover type doctrines; I don’t think my use implies this nor was it my intent to imply it. However, I could accept that I am pushing forwards a ‘purpose for humans’.
p.s.
My tease regarding nihilists requires knowledge of a highly esoteric debate following from a number of further esoteric writings made by Nietzsche that are, none-the-less, related to the subject matter I raise i.e. anti-life?.