First, after having researched this issue, it is my belief that ascribing the earth as being millions of years old is simply the result of a parroted phrase rooted not in science but instead as the foregone conclusion of a naturalistic worldview. You see purely naturalistic, atheistic science only thinks in terms of millions or billions of years for one simple reason - because these same scientists think that allowing for a great span of time gives more credence to the plausibility that life came to it's present state by purely naturalistic causes. If a frog suddenly turns into a man, we all know it's a fairy-tale. But, given enough time, it makes it sound more plausible, even scientific, that evolution could have happened. But the frog that becomes a man, whether it happens quickly or over a billion years, is still a fairy-tale. No one has ever seen a frog become anything other than a frog. My basic issue is there is no actual evidence that the earth or universe is millions of years old and adding or subtracting time doesn't solve the issues raised in what is known as the anthropic principle. I'm not suggesting the earth is 6,000 years old or 6 million, I'm just saying the evidence for the old earth model is not backed by any more or less evidence than those who ascribe to a young earth model. Further, time does not solve the problems of naturalistic origin.
Secondly, let's just assume that the earth is millions or even billions or trillions of years old, the inescapable fact is no matter how much time we allow for, there is no answer to the origin of life in science. Sure we can theorize and postulate and try to recreate the beginnings, but we can never be certain. The reality is no matter how you spin it, in order to believe life began in a purely naturalistic way, you must also believe that life came from nothing (abiogenesis) - that non-living material can somehow come to life. It is theorized, at a high level, that water being rained down on the earth for millions of years, formed a primordial soup out of which the first life forms emerged. Unfortunately for those who ascribe to this theory there is no actual evidence for it. It has never been observed - ever. Even in the most carefully controlled modern lab tests where real-life variables are artificially removed (because they would instantly destroy the possibility of experiment) and stimuli introduced, life never emerges from non-living matter. I liken the belief that life can come from non-living matter to the same logic of a time when people believed flies came from raw meat. Any desires to cling to such arguments are not rooted in science but in an underlying world view. Origin is where science ends and metaphysics begins - anyone who tells you otherwise is not being honest about the facts. Even men like the famous modern day atheistic-scientist and author Richard Dawkins (The God Delusion) run into major problems when confronted with this issue of explaining the beginnings of life. How can something come from nothing? Simple - it cannot. In an effort to cling to his theory he employs pure atheistic metaphysics, having written and been recorded expressing the possibility of theories such as panspermia (life transplanted on the earth from other life forms in the universe). Even if life were transplanted from other life forms (we're really leaving science in the dust now) we still have the massive problem of a first cause. We cannot have an infinite regression of causes. Ultimately, there has to be a first cause.
So in the end (or shall we say beginning) life either came from nothing spontaneously or was caused by a first cause. The first cause would have to be independent of time, self existing and sustaining, intelligent, and powerful - in a word, God. The alternative is a world with no independent first cause and spontaneously generated life. What I want to clarify for anyone who is curious, science and specifically biology alone cannot solve the question of origin. It also cannot explain phenomena like meaning, truth, consciousness, beauty, ethics, literature, art, religion, or even science. To come up with a reasonable conclusion to such realities requires employing disciplines of science (physics, biology, and mathematics) as well as employing rationality (metaphysics, ethics, epistemology, and philosophy). Simply adding millions of years to the equation and saying "abracadabra" over it doesn't make for a cohesive scientific explanation of origins.