I’ll go out on a limb. I believe that GOD perfuses the Christian Bible, but I also credit the fact that Creation began when astronomers and physicists say it did. We can quibble over how that makes sense some other time – I’m only going to talk science as the scientific community knows it.
The population of stars we can ‘count’ – estimate – is roughly 100 billion per galaxy, and 2 trillion galaxies. Not many people run into these numbers, but their size likely maximizes the likelihood of life developing multiple times.
How many stars, on average, have a suitable candidate planet in orbit?
a) Presence of a full kit of elements requires that the star / planet system arise from the aftermath of a collision of two neutron stars. That is the only way current theory has found to make more than the first couple dozen elements.
b) Presence of an earth-like planet, i.e. rocks and water and iron core (for that, later) in a pretty narrow Goldilocks zone. Our planet was an ice ball for a hundred million years or so – then tectonic activity loaded the atmosphere with CO2 etc. Not going to recite the geological history of the planet here, but it has seen both ice at the equator and heat that let plants live at the poles. To this untutored brain, that says the Goldilocks zone almost has a negative width! A teeny bit colder, or a teeny bit warmer, and the planet may still have engendered cellular life, but the likelihood of it ever becoming hi-tech is slim to none.
c) Presence of a large, stabilizing moon. Evolution of species works well when the climate changes slowly. But an unstabilized planet will have its axis of rotation precessing such that there will be eras with one pole in constant daylight and one in constant darkness, part of the time. Earth has vastly better odds of evolving its plethora of species because the moon anchors its axis to about 23 degrees of tilt relative to its orbit around the sun, giving us seasons. They’re bad enough, but life keeps finding ways. If the ‘seasons’ lasted millions of years, life would still find a way – maybe.
d) That iron core. Earth’s core spins because earth spins; this provides a magnetic field, and the magnetic field deflects vast amounts of damaging particles that leave the sun. Life on board the Space Station isn’t terribly unsafe, but the area where solar emissions encounter the earth’s magnetic field isn’t a healthy place. Moon astronauts got through it fine, but they zoomed through it in a relatively brief passage, coming and going. Without that iron core we might not even have an atmosphere. Venus has a crushing super-blanket of CO2; Mars has the same density at the surface that earth has somewhere above 80,000 feet. The SR-71 got up that high; it had to go Mach 3 and above just to get enough air into its engines, and enough air hitting its wings, to stay that high. SIDE DATA POINT – without the moon, the earth’s magnetic field would have spent millions of years head-on to the sun, letting those atomsphere-depleting particles eat away at the atmosphere.
E1) Now we get to the real nitty-gritty. The shopping list you take to the hardware store includes a bunch of lipids – sheets of the stuff. The nucleic acids are already on hand, bubbling around in the hot ocean water. Every ten degree centigrade jump in temperature doubles the speed of a chemical reaction, and life in our oceans appears to do fine at temperatures fifteen or more tens of degrees centigrade above what we see on the surface. Ten doublings is roughly a thousand times faster. And there are billions of gallons of hot soupy water. Things align and break down constantly.
E2) But it takes enzymes to make RNA chains; DNA comes later. It takes other enzymes to ‘do stuff’ based on the RNA. And all of this has to happen inside a lipid shell. And the stuff trapped inside the lipid shell has to stumble across a way to replicate itself. AND the self-replicating stuff inside the lipid shell has to find a source of chemical energy because every single chemical change takes some inputs, uses energy, and results in something with a changed energy state.
E3) Energy and mass are interchangeable – combine two H’s and an O to get a three-atom molecule. This releases energy, and the H2O winds up with a teeeeensie bit less mass. Love that technical term. H2O has less mass than two free H’s and the free O. Thank Einstein for the math to figure out just how little mass that is, but it’s non-zero. In other words, to be ‘life’ this assemblage must also manage an energy budget where new chemical bindings that absorb energy, i.e. are the opposite of burning, get balanced out (paid for) by other chemical reactions that release energy.
E4) In short, the piling-together of interrelated circumstantial jackpots beggars the imagination. It works now, but how this enormously complex operation happened for a first time is beyond easy calculation.
I allege no answer to the mystery of why life exists at all. It is ‘any idiot knows’ obvious that life exists here; but there is no real future in letting idiots do your knowing for you. Numbers like sextillions of stars (a 2 with twenty-three 0’s following it) make it seem likely that some other planet, at some time, also had life arise. But my nickel says that GOD was so lavish as to make that many stars, just to guarantee that, after watching long enough, and with patience and excitement no human can comprehend, the exultation of life would occur.
We measure it as 8.8 billions from bang to our sun igniting; at time 9.2 billion years earth coalesced. At time 10.8 billion years life had begun leaving marks in the sedimentary record; and at time 13.2 billion years sexual reproduction came along, and that (pun intended) spawned an explosion of species.
So, could that have happened somewhere else, “Long ago in a galaxy far, far away?” To me, believing that question has an easy answer is folly.
Oh, and Another Thing 