Why meteorites looked so different hundreds of millions of years ago

Contributed by
Jan 26, 2017

Meteorites may appear to be unglamorous space rocks that have seen more than a few rough days (or aeons), but what they looked like before a prehistoric space collision could reveal more than just beauty secrets about our solar system.

When asteroids, planets and moons collide, they leave behind fragments of themselves that become meteorites. The composition of these remnants that eventually crash to Earth is like a chemical fingerprint that tells scientists which celestial body or bodies each one broke off from after the impact. Traces of minerals inconsistent with the rest of the rock tell which other floating objects it encountered. Dissecting meteorites even further enhances the understanding of the genesis and evolution of our solar system.

466 million years ago, before the T-Rex ever ruled, an asteroid shattered when something unexpectedly rammed into it and the meteorites left in its wake showered down to Earth. The meteorite flux (diversity of meteorites that plummet to our planet's surface) has changed drastically. Scientists have now been able to piece together an unprecedented reconstruction of the meteorite flux before the epic crash. What their findings show about today's imperfect meteorites is that they were rare prior to the collision, while those we rarely get a glimpse of now were abundant in the distant, pre-dinosaur past.

Example of a chrome spinel magnified by an electron microscope.

As asteroid collisions leave behind cosmic debris with each crash, meteorite flux goes through many iterations over geological time as different elements and chemical compounds are introduced. The scattered shards of one crash become dominant as those of another fade into the vast darkness. Micrometeorites, or particles of meteorites often found in fossilized sediment, have revealed that their immense variety of chemical compositions represent far beyond just one extraterrestrial flux.

Investigating scientists led by Philipp Heck of The Field Museum in Chicago studied micrometeorites in sedimentary rock that dates from a million years before the asteroid collision and published their findings in Nature Astronomy. There was one type of crystal sought after because of its almost indestructible nature. "Chrome spinels, crystals that contain the mineral chromite, remain unchanged even after hundreds of millions of years," Heck explained. "Since they were unaltered by time, we could use these spinels to see what the original parent body that produced the micrometeorites was made of."

Chemical analysis of the spinels opened a portal to primitive space. Some were even the remains of a billion-year-old collision experienced by Vesta, the brightest asteroid human eyes can see as a tiny twinkling spark in the night sky. After finding that the meteorites which hurtled to Earth before the crash were drastically different than those that followed, Heck’s team concluded that mostly debris from recent asteroid run-ins comprises present-day meteorite flux.

"Ultimately, we want to study more windows in time, not just the area before and after this collision," Heck anticipates, "to deepen our knowledge of how different bodies in solar system formed and interact with each other."