The Earth has been around for about 4 billion years and supposedly life got started shortly there after. Human DNA has a zillion pairs of the encoding molecules. If life has been evolving for 4 billion years, and we are adding or changing a letter in our secret code every so often, is there enough time to cobble together a DNA molecule with a zillion pairs?
From the Wikipedia article on DNA: The set of chromosomes in a cell makes up its genome; the human genome has approximately 3 billion base pairs of DNA arranged into 46 chromosomes.
From the Wikipedia article on Evolution: Highly energetic chemistry is thought to have produced a self-replicating molecule around 4 billion years ago and half a billion years later the last common ancestor of all life existed.
Okay, there are only 3 billion base pairs in human DNA, not a zillion, and since life has been evolving for 3 billion years, more or less, that means we only need to add one pair a year in order to get our enormously long strands of DNA.
Once life got started, it probably wasn't too long before there were a zillion copies of it, each one on it's own evolutionary path. Errors were occasionally made in the copying process. Some of these errors proved to be beneficial and some didn't. Beneficial errors helped cells to survive, detrimental errors did not. Some of these errors made the DNA longer.
So, yes, there has been enough time to assemble a set of chromosomes with 3 billion base pairs.
Meanwhile, Worldwide army of scientists cracks the 'junk DNA’ code
Via Graham Hancock.