Meteorites, the remnants of space rocks that have impacted Earth’s surface, are windows to ancient times. These beautiful assemblages of mineralogical marvels formed around the same time as the Solar System’s rocky worlds and asteroids, which hints at how these terrestrial titans originally came to be.
That’s why meteorite Northwest Africa (NWA) 11119 is so exciting a find. As explained in a stunning Nature Communications paper, it’s 4.564 billion years old, give or take a few hundred thousand years. Earth is around 4.54 billion years old, which means that this former meteor was potentially zipping around the early Solar System before our world even crystallized into being.
That means that it’s not just an insight into how precisely the terrestrial planets appeared from the miasma, but what type of processes were occurring even before then. Turns out that, according to the University of New Mexico (UNM)-led team, there was a decent amount of advanced volcanism taking place back then.
In order to understand why, though, we need to explore what NWA 11119 actually is, and what it isn’t.
Found back in 2016 within a sand dune in Mauritania, it was quickly snapped up by a meteorite collector. It was then sent to Carl Agee, the director of the UNM Institute of Meteoritics, who gave it to his graduate student – and lead author on the new paper, Poorna Srinivasan, to study.
1119 is part of a class of meteorites known as achondrites. They’re best understood, methinks, when contrasted with another type of meteorite. Their counterparts, chondrites, often contain spherical, silica-rich inclusions – called chondrules – whose glassy forms betray their origin story: they only underwent sudden, sporadic heating and melting events, which indicates they were never part of a larger planetesimal or even a fully-grown planet.
Achrondrites, as the name suggests, lack these glassy inclusions. Instead, their textures and minerals indicate that they underwent long-term, high-temperature (and pressure) melting.
This suggests that they spent much of their lives within larger objects, from asteroids (asteroidal achondrites) to planets (primitive achondrites). Lunar and Martian meteorites are types of achondrites too.
Typical achondrites have revealed that there was plenty of long-term melting going on in the Solar System billions of years ago, with huge collisions between asteroids and worlds shattering them and sending evidence of this phenomenon hurtling our way.
Now, volcanic rocks on Earth develop through a complex plumbing network of magma reservoirs that partly cool, partly crystallize, re-melt, move around, and chemically evolve.
Those that haven’t evolved too much have lower amounts of silica and are like the type of rock that the lava from Kilauea is cooling and forming right this very moment. Give the magma more time to evolve using a more complex plumbing system, and you get more silica-rich materials, like the sort that forms under Mount St. Helens.
Several recent discoveries have revealed mineral inclusions in meteorites that are more like some of the silica-rich rocks we have on Earth. 1119 is similar in this respect, but as it’s the oldest and most silica-rich igneous meteorite known to science, it reveals that this advanced volcanic process happened right as the embers of the Solar System were coalescing.
Much of it is made of tridymite, a very high-temperature version of silica, and something that hints at a long period of magmatic evolution. In fact, its geochemistry is similar to two other strange meteorites – Northwest Africa 7235 and Almahata Sitta – which implies they have the same source, or “parent body”.
Although currently unidentified, it was clearly huge enough to permit such complex melting, and one that was destroyed at the start, or just before the start, of our Solar System. Whatever it was, it was certainly fairly similar to Earth once upon a time.
So 1119 doesn’t just provide a window into an alien world’s past, it lets us see through the looking glass into the birth of our very own planet.