Four decades ago, the sky fell. That’s the poetic way of putting it. The factual way to describe it is that rocky space debris totaling a significant fraction of Earth’s mass cascaded across the planet over the course of two days. Hardly a square mile of the world was spared from some kind of meteor strike, from rocks the size of bullets up to ones the size of airplanes.

Approximately half a billion people died from the impacts and their immediate collateral damage. The same number died in the next few days from the massively destroyed infrastructure, fires, and tidal waves. Even more would die over the next few years, from the famine caused by the green haze diminishing the light of the sun and from cancer caused by the massive influx of radioactive particles. By the mid-1980s, humanity had been reduced by nearly half what it was before the catastrophe.

Much of the debris was a strange, green crystalline rock, which came to be called Viridian. Safe to hold briefly, it became apparent that it was nonetheless highly radioactive. The large shards were quickly collected from craters by local governments, but the small fragments and dust were what led to the steep rise in cancer throughout the world’s population. The years of haze also created immense static across the radio waves, and new age nuts swore that it had similarly silenced the world’s magic.

But, humanity will overcome. Far less destructive than global thermonuclear war (and fortunate neither superpower had viewed the impacts as an attack), Viridian proved far safer and more useful than plutonium. Within a few years, the worst of the haze had been denatured by weather and sunlight, diminishing to a slightly-elevated background radiation. The vast stores of crystals could be harnessed for much-safer nuclear power to try to bootstrap global technology back from its nadir. And the massive crisis, shared tragedy, and loss of competing mouths to feed had united the world in a way that nothing else could. Scientists worked across national lines to solve the problems of rebuilding infrastructure, curing cancer, harnessing the new material, and looking to the skies to prevent such a disaster from ever happening again.

It did not take long for the world’s astronomers to realize that this was not some random strike. The trail had followed the path of a small, recovered spacecraft that crashed ahead of the tide of rock, somehow guided through space. If not for the fortunate timing of an alignment with Mars, scraping off the bulk of the debris cloud to impact the red planet, Humanity might have gone extinct. Earth had been saved by a matter of hours in celestial alignment.

But if there was some great enemy on the other side of the galaxy that had tried to remotely bombard Earth into an apocalypse, they would find humanity ready. In addition to great strides in technology, the planet had an unexpected resource: individuals with inexplicable powers. Shocking numbers of children born after the skyfall began to demonstrate these abilities, believed to be mutation from the Viridian’s radiation. The vast majority could do little more than parlor tricks, but there were others that could do more. Some few turned their abilities to crime and war, but the greatest of them became protectors.

You are the world’s premier super group: some of the strongest of the Viridian Children, coupled with some of the brightest engineers to harness the crystal for powered gear. When the world is threatened from within, you leap into action. But everyone knows that you are really preparing for what might happen if the aliens that launched the attack try again.

At least you were.

Years of research has finally been verified. The “attack” may have been a cosmic accident. The “missile” could have been an intergalactic escape pod for a single refugee, accidentally sweeping part of an exploding planet in its wake. All the astrophysics backs it up, tracing the path of the Viridian to a distant solar system where a shattered planet orbits a red giant sun in its habitable zone. If this doomed planet had exploded mere hours later, Earth would have received the full blast. But the real tragedy is, a day earlier, and a passing sweep of Jupiter might have collected the majority of the debris safely, leaving both Earth and Mars barely scathed. A sad and immutable fact of history, certainly.

Except that the particle physicists at Star Laboratories have begun to talk of some kind of “speed force” that might make faster-than-light travel possible… developed with the idea of space travel and defense, some are murmuring that it could be used for time travel.

And there would be many people interested in going back forty years to try to give the Earth a second chance…

This idea is largely inspired by Umbrella Academy and Avengers: Endgame. What if the greatest heroes from a recovering post-apocalyptic timeline washed up in a version of history where they’d be inevitably viewed as villains? In the recovering world they came from, the PCs are basically the Justice League. But in the prime DC timeline, they’re a bunch of meteor mutants or using Kryptonite-powered tech, and Superman takes a keen interest in those. Even should they convince this world’s heroes they’re not villains, they still have every incentive to try to restore the timeline that contains everyone they’ve ever loved, and the new powers that be can’t have that.

Incidentally, for the scenario above, I think the inciting incident is a few surviving White Martians infiltrating Star Labs and trying to change the timing of Krypton exploding enough that Earth takes the full brunt rather than Mars. But the heroes intervene, somehow speed up the process (possibly because Braniac notes their presence), and wind up leaving both Earth and Mars intact, giving rise to the standard DC timeline of your choice.