Around 3.9 billion years ago, on a Tuesday, the Moon was experiencing a hushed state of affairs.
To be fair, most days on the Moon are quiet — apart from the occasional moonquake. The day-to-day lack of activity on the surface means there’s usually not much making noise in the first place. Even if something did crack, or creak, the absence of an appreciable atmosphere prevents you from hearing it.
But back then, the rest of the solar system was pandemonium. Billiard balls the size of planets were flying about all over the place, crashing into one another and breaking up into gigantic shards. By this point, giant impacts had been in vogue for an eon. The Moon’s own birth, 600 million years earlier, probably came about when a Mars-sized not-quite-finished world rudely smacked into a nascent Earth, then blanketed by a planet-wide magma ocean. Hot cinders flew off into orbit, which cooled and agglomerated into a baby Moon.
That was far from the end of the destruction derby at the dawn of the solar system. Massive rocks kept hitting other massive rocks for hundreds of millions of years. Some hit the Moon, punching especially giant holes in the lunar nearside — the side of the Moon that now always faces Earth.
These titanic impacts didn’t happen every single day. There were large periods of silence between each, at least when viewed on an anthropological and not astronomical timescale. But one day, roughly 3.9 billion years ago, the Moon and a space rock 160 miles long had an explosive encounter. The tranquility was shattered as this 25,000-trillion-ton projectile moving at a speed of perhaps 52,000 miles per hour — 30 times faster than a particularly speedy bullet — hit the lunar nearside.
When I mention these numbers to Dan Moriarty, a lunar geologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, he starts laughing.
“It’s inconceivable,” he says. “There’s no intuition for that scale.”
If you could see the impact from Earth, you would first see a bright flash of light. “The rock vaporizes, and you’d have this incandescent stream of vaporized impact of target rock spewing out,” says Moriarty. Glowing embers would flit about briefly in the darkness, drifting out into the great expanse before being extinguished by the frigid vacuum. Enormous chunks of Moon and asteroid would spend the next day or so flying up into space.
The Moon was much closer to Earth back then, looming far larger in the sky than it does today. “We would have gotten hit,” says Peter Schultz, an expert in impact cratering at Brown University. “There would have been a hell of a meteor shower on the Earth.”
Much of the impactor would have been obliterated on impact, which involved more energy than could be unleashed by the combined force of every single nuclear weapon ever made. Fragments of rock that initially survived the encounter shot through the lunar crust, digging out giant trenches; it was as if the Moon was made of soft butter and was being attacked by a planet-sized fork. At ground zero, the preternaturally high temperatures and pressure annihilated the lunar rock, creating ephemeral silicate clouds and a giant, temporary sea of molten rock perhaps 12 miles thick — twice the height of Everest.
“If you were far enough away or had good enough shielding, it would be absolutely incredible to see,” says Moriarty, still laughing at the absurdity of it all. The dust cloud may have obscured the Earth’s view of the Moon for some time afterward.
The Moon had a new 710-mile hole in its face. Named Imbrium Basin, it was seven times wider than the crater left behind by the dinosaur-aggravating asteroid that hit Earth 66 million years ago. And at this point, you’re probably wondering how the hell we know any of this.
Sometimes, scientists look at the scar tissue left behind on worlds, pick appropriate mathematical and physical parameters, plug them into a computer program and run some simulations to replicate momentous impacts. Other times, they use a 14-foot cannon to fire projectiles at 16,000 miles per hour at dusty surfaces in a laboratory.
At the NASA Ames Research Center in Mountain View, California you can find the Vertical Gun Range. Within is said cannon, designed to simulate speedy, major impact events such as the one that made Imbrium Basin. Firing one tiny aluminum cannonball after another at a sandy, pseudo-lunar target at 100 times the speed of sound, Schultz and his Sandia National Laboratories’ colleague David Crawford could tease out the physics and dimensions of the Imbrium impact event in a scaled-down laboratory setting.
It’s a bit like throwing a snowball at something at an angle: it creates a splayed pattern of debris. If you could play this event backwards in time, says Schultz, you could determine what the snowball was like and how it hit the surface. And after plenty of experiments, and some debris pattern time inversion, they concluded the only way you could get Imbrium’s striking grooves and a crater of that size was if a rock the size of New Jersey crashed into the Moon at an oblique angle.
This monumental impact created some seriously surreal products. A tsunami of molten rock mingled with bits of solid lunar crust, forming disfigured rocks called impact melt breccias. Upon cooling, these boulders of warped rock and crystallized soup littered the realm.
Around 250 million years later, those around the edge of Imbrium Basin would have seen lava begin to erupt into the crater, from below or from the sides, pooling up to the elevated shorelines and creating a Hadean sea named Mare Imbrium — the ‘Sea of Rains’. Real water wouldn’t have fallen from the sky — as the lava geysered and effervesced, the only rain on Imbrium would be droplets of molten rock, quickly cooling into tiny, perfect glass spheres.
The Moon cooled as it shrank. Pathways for magma to escape to the surface snapped shut, and without enough heat left trapped inside, epic oceans of lava stopped erupting into the Moon’s multiple, massive impact basins. The quiet days on the Moon got even quieter. Apart from the occasional moonquake, and the odd meteorite impact, silence reigned.
Another few billion years passed — until, in 1969, spacefaring explorers paid their first visit to the silvery kingdom. More came, jumping about, driving around, posing for photographs and hammering mechanical marvels into the soil. And just before Christmas in 1972, Eugene Cernan and Harrison Schmitt, the latter of which remains the sole geologist sent to the Moon, saw a curious-looking boulder standing alone near the south-eastern edge of the Sea of Serenity.
The last humans to walk on the Moon bounded over to the boulder, gawped at its shiny crystals and Swiss cheese-like texture, and ultimately deemed it worth some scientific thievery. They broke off a segment of it – Lunar Sample 76015 – packed it up, and along with a bunch of other rocks, flew it back home.
The sample began its residency at NASA’s Lunar Sample Laboratory Facility at the Johnson Space Center in Houston, Texas. Like many of the other rocks brought back by the Apollo missions, it was broken up into pieces for scientists to prod and poke in the hope that they would clue us in to the formation and development of the Moon. They did, but they also taught us about our own world too.
Evidence of Earth’s earliest epochs has been destroyed by volcanic eruptions, flowing water, the destructive shift of tectonic plates, the weather and the proliferation of life. The Moon lacks any such erosional or self-destructive capabilities. And it’s so close to Earth, and mostly made of the same building blocks, that its ancient history is Earth’s ancient history. Our planet may have erased its distant past, but some stories - from how Earth got all its water, to the pummeling it received at the hands of asteroids over eons of time - remain locked in lunar matter, waiting for us to decipher and read them.
Several American presidents have got their hands on some of these geologic marvels. Nixon handed a fair number away to foreign diplomats, many of which managed to lose their shards of another celestial plane, through mischief or misplacement. And in 1999, on the 30th anniversary of the first lunar landing, Clinton was handed a hefty Moon rock by the Apollo 11 trio of Armstrong, Aldrin and Collins. He later said that this sample was “the most valuable thing I had for perspective in politics in the White House.”
One 12-ounce piece, named Lunar Sample 76015,143, was part of that same lunar shard removed from an ancient lava sea by the Apollo 17 moonwalkers. It spent some time in the German Museum of Technology in Berlin, before NASA, at Biden’s request, lent it to the newly inaugurated president to display on his bookshelf.
"You usually see statues of figureheads in politicians’ offices," says Marie Henderson, a PhD candidate of planetary sciences and lunar aficionada at Purdue University. This Moon rock doesn’t just have an epic origin story — it represents the 375,000 Americans that worked on the Apollo program. “It’s proof of what can happen when you invest in science and technology,” she says. “I think people would rather see that than a statue.”
Its official purpose is to showcase the administration’s commitment to scientific progress, returning to the Moon, and visiting Mars and the worlds beyond. But there is also something to be admired in its journey to the White House. Over the past four billion years, this small piece of rock has experienced unfathomable drama, turmoil, destruction.
And yet, it survived.