Fifteen thousand million years ago the universe was no bigger than the dot at the end of this sentence.

A tiny, tiny fraction of a second before that – but there was no fraction of a second before that. There was no time before the universe began, and without time there can be no “before.” There was no space, no time, and no matter.

Two minutes after time began (some say one and a half minutes, others three) the universe had cooled to one billion degrees, and matter as we know it began to assemble. Neutrons paired incestuously with their proton offspring to form creation’s first atoms – heavy hydrogen, otherwise known as deuterium. Deuterium fused into helium and matter began to change.

About half an hour the universe changed: now it was three quarters hydrogen, one quarter helium. The pace of change slowed. It took seven hundred thousand years before the universe cooled enough to become transparent to light. By then, matter had formed itself into almost a hundred different elements. It took a hundred million years for that matter had formed itself into almost a hundred different elements. It took a hundred million years for that matter to clump itself into galaxies, and for the first stars to shine.

One star – not especially different from its companions – had spectral class G2, meaning that its surface temperature was about average (six thousand degrees) and the light that it emitted showed a prominent trace of calcium. Like many stars, it was enclosed in a cloud of cosmic debris – stardust blown across the intergalactic space in shockwaves generated by explosions in the galactic core.

As the universe grew older, and colder, and larger, this particular cloud of stardust – like many others – began to condense, the grains sticking to each other , to form irregular lumps of methane ice, dense clouds of gas, fragments of rock. As it condensed, it also collapsed into a flattish disc, spinning on its axis, a swirl of cooling matter that collided, bounced, broke, stuck aggregated. As time passed, a mere instant on cosmic scales, the clumps became fewer, but bigger. Crushed under their own gravity, they formed flattened spheres – planets. The G2 star acquired a solar system.

None of this was especially unusual.

Each planet, forming in its own particular place, found itself in possession of the features that its mode of formation would naturally create – a rocky core, a methane-hydrogen atmosphere, a surface flowing with molten metal or dotted with lakes of acid, encircling companions. Each planet acquired its own identity. This in particular was true of the third planet, counting outwards from the central star. Much of its surface was covered by a thin layer of water. It had an atmosphere, mostly nitrogen. And its surface temperature was within the range at which water remained liquid. Although no other planet in this particular solar system resembled the third in these respects, it was probably much the same as many other planets around many other stars in many other galaxies.

Everywhere, even in the depths of intergalactic space, atoms bumped against each other and stuck to form molecules. On the third planet this happened more often than in the vacuum between the stars, because there were more atoms to bump into. The individual features of the third planet constrained the kind of molecule that occurred, producing structures that would not have occurred on a methane world or an ice giant. One day there arose a collection of molecules that could make copies of itself – a replicating system. Perhaps it came together accidentally in the primal soup of the oceans, perhaps it was given a helping hand by the receptive surfaces of rocks or clays. However it happened, the replicator did what replicators do – it replicated. Over and over again. After a fairly short time the planet became distinctly unusual, its chemistry subverted and reorganized by the voracious replicator, The replicator made the occasional mistake, but some mistakes could also replicate, and soon a kind of long-term War of the Replicators was under way, as ever more sophisticated molecular collectives did battle for the right to continue replicating.

It all got rather complicated.

For instance: one group of replicators acquire the knack of converting starlight into food.

For instance: an early success, the bacterium, attained such numbers that one of its metabolic by-products, the corrosive gas oxygen, came to occupy a substantial portion of the planet’s atmosphere.

For instance: other groups of replicators evolved the ability to leave the solid ground and soar upon the gases of the atmosphere.

For instance: sixty-five million years ago an especially successful type of replicator was exterminated, planetwide, by the impact of a large rock. Other tiny hairy warm-blooded replicators suddenly found that their main competition had vanished from the face of the third planet. And their rapidly diversifying successors exploded across continents and oceans.

For instance: today, two of the descendents of those tiny creatures are busy delineating their own limited version of the entire story in strange and geometric symbols, impressed in contrasting pigment upon sheets of compressed white vegetable matter, in the hope that other creatures of similar kind will scan the sheets with light-detecting sensors – and in some inexplicable manner imbibe meaning and significance and make them part of themselves. Typically for these replicators we find a tiny portion of the ungraspable universe making a glorious, hopeless attempt to encapsulate that awe-inspiring whole inside its own tiny form, improbably employing weak electrical impulses that scuttle along a network of a trillion tiny fibers – vibrant, alive, and even more ungraspable than the universe that it is attempting to grasp.

A circle closes.

A mystery opens.