Did you know, we share genes with celery?
The advent of DNA, or perhaps just RNA, plus a host of convenient enzymes and a surrounding lipid shell, is virtually impossible. Emphasize *virtually* – but not actually impossible. Whichever mechanism pleases you most, early in Planet Earth’s history replicating cells existed. They made detectable clumps with a vague geometry that fossilized into ‘stromatolites’ (look that up) and that’s how we can tell, today, that reproducing life existed.
These stromatolites occur in parts of the earth’s crust which happen to be 3.6 billion years old, and which also happen to be exposed at the surface. Rocks are hard, but when you put them under enough stress, you learn that nothing is perfectly rigid. Planetary crust is, on billion year scales, very plastic, so attempting to replay the ebb and flow of plate tectonics, crust erosion and uplift, etc. is PhD level stuff.
If you don’t believe PhD’s know how to tell the truth, please stop reading here.
After about another 3 billion years, i.e. about .6 billion (600 million) years ago, random accidents to the original versions’ DNA had spun off enormous numbers of variations. A huge preponderance of the variations were harmful, but a few turned out to lucky rolls of the dice. Across 3 billion years the population of varieties had become colossal. Lots of DNA swapping happened, too. Also, symbiotic specialization where one species hosted another, which got food and protection in exchange for specializing in some kind of metabolic processing.
Today this kind of symbiosis is part of all animal life, and the inclusions are detected as mitochondrial DNA. The female egg is loaded with them; the male sperm seldom has any, so by comparing mitochondrial DNA siblings are easy to connect to a mother, maternbal grandmother, etc.
At that changeover point, 500 to 600 million years ago, something came along which exchanged DNA on a colony level, i.e. invented 3-D sex. The critical advance was the ability of two members of a given type to ‘breed’ together, i.e. they reproduced by forming a joint product, a single cell containing half of the first one’s DNA and half of the second one’s DNA. This was called the sexual revolution.
The one in the 19070’s caught some notoriety, but back then it led to an explosion of new species. Winding up with pairs of chromosomes swappable half-half to reproduce a brand new set of DNA unleashed the power of evolution. Across that first 3 billion years evolution operated like a unicyle. The advent of gene-swapping reproduction among complexly structured units put evolution on four wheels, if you will, as in “off to the races.”
The “Pre-Cambrian Explosion” is the name for that tiny (in earth’s terms ) slice of time, a few tens of millions of years, during which countless species developed into (if I recall correctly) four ‘kingdoms’ – animal, vegetable, mold and bacteria, please correct me if I’m wrong – and in the animal kingdom several dozen “phyla.” A ‘fifth’ kingdom is the archaea, which consists of things related back to the earliest days, things which didn’t develop into any of the four primary classes. And all of them are of course single-cell forms.
At the start a dozen complete phyla emerged in a short span of time – but two-thirds of these died out. Since then evolution has wrought roughly three dozen current phyla; again please correct me if I misspeak, but the basic point is that species developed and diverged.
In theory every single DNA-based organism on this planet is a mutated offspring of some first surviving and self-reproducing cell. The odds against that first cell are are stunning, but there are also two hundred sextillion stars in the knowable universe – a two followed by twenty-three zeroes. It’s wildly unlikely that more than one of these stars out of a handful of powers of ten – one in a million? – is likely to have an earth-like planet in orbit around it. So slice off six or eight of those 23 zeroes. God knew what He was doing when He said, “Let there be light,” and released the Word to fill the universe with signs and wonders, and two trillion galaxies each with perhaps a hundred billion stars.
Sol was the lucky star that got us.