Published: November 12, 2014

Fossil Meteorites Arrive at The Field Museum

Philipp Heck, Sr. Director, Negaunee Integrative Research Center; Robert A. Pritzker Curator for Meteoritics and Polar Studies; Head, Robert A. Pritzker Center, Negaunee Integrative Research Center

They are the “Mona Lisas” of meteorites – out of over 50,000 known meteorites, only 101 of them are fossilized, and four of them will be on display at The Field Museum.

These meteorites have a fascinating story! Back in 1952, the manager of a limestone quarry in Sweden that was once an ancient sea floor noticed an unusually dark object in a slab that one of his workers had cut and set aside. He approached a paleontologist about it, who set it on a shelf in his office and forgot about it. 27 years later, a mineralogist who was interested in meteorites walked into that very same office, and exclaimed, “That looks like a meteorite!”

The discovery of this meteorite nearly three decades after it was removed from the quarry led to a systematic search for more—in fact, workers were trained to recognize them. Over the next 20 years, 101 fossilized meteorites were uncovered in the quarry, which is 100 times more than we would expect. Philipp Heck, Robert A. Pritzker Associate Curator of Meteoritics and Polar Studies at The Field Museum, tells us why.

“These meteorites all came from the same source,” said Heck. “The breakup occurred somewhere between Jupiter and Mars – nowhere near Earth. We know that because the collision generated fragments ranging from millimeters to feet in diameter that have been found in Russia, China and Sweden, indicating that this was a global event. In fact, I would venture to guess that fragments of this meteorite can even be found on Mars.”

Like all fossils, the 101 meteorites that have been recovered in the quarry became fossilized when the original material was replaced by other minerals during the transformation of the soft seabed to sedimentary rock. However, these meteorites contain a mineral called chromite that was preserved in its pristine form that matches the composition of L chondrites – the second most abundant type of meteorites that fall to Earth today.

“There is one exception,” said Heck. “Out of the 101 fossilized meteorites, one of them did not match the composition of the L chondrites. We do know that it took the same amount of time to reach Earth as the others, so we think it may be part of the projectile that caused the parent asteroid to break up.”

Meteorites are dated using products of cosmic ray irradiation. Cosmic rays hit everything that flies through space and is not protected by a magnetic field or a thick layer of rock. For example, when a cosmic ray hits a silicon atom that has been exposed on the surface of a meteorite, it causes the atom to break apart and form noble gases, which are inert – meaning that once they form, they stay put. Scientists can measure the concentration of these gases and use them to determine the time it took for a meteorite to fall to Earth, since the meteorites were protected inside the parent body prior to the breakup.

“The first of these fossil meteorites arrived on Earth about 100,000 years after the breakup, and the most recent ones that were found took about one million years to arrive.” said Heck.

It sounds like a long time, but it’s actually extremely fast! The orbits of meteorites change over time, until they cross the Earth’s path, and the probability of that ever occurring is very low, given where the collision occurred.

“That being said, these meteorites are extremely rare, and we will definitely be keeping our eyes out for more,” said Heck.


Philipp Heck
Sr. Director, Negaunee Integrative Research Center; Robert A. Pritzker Curator for Meteoritics and Polar Studies; Head, Robert A. Pritzker Center

Philipp R. Heck serves as the Senior Director of Research at the Field Museum. Research at the Field Museum is conducted in the areas of Earth and Planetary Sciences, Life Sciences, Anthropology and Archeology, and is united in the Negaunee Integrative Research Center. Heck is the Robert A. Pritzker Curator of Meteoritics and Polar Studies at the Field Museum of Natural History in Chicago, IL in the Science & Education department and a Professor (part time) at the University of Chicago's Department of the Geophysical Sciences and the College (https://geosci.uchicago.edu/people/philipp-heck/). 

Heck's research focuses on presolar grains to understand our parent stars and the history of our Galaxy, early solar system materials, asteroids, and on the delivery history of extraterrestrial matter to Earth. For his research he studies the mineralogy and geochemistry of meteorites, micrometeorites and space-mission returned samples and also of fossil meteorites and micrometeorites found in Earth's sedimentary record. Heck joined the sample analysis team of NASA's OSIRIS-REx sample return mission. Heck was a member of the international research consortium to find and study the first modern interstellar dust returned by NASA's Stardust Mission. Heck is an executive committee member of the Extraterrestrial Materials Analysis Group (ExMAG) and is chairing the Microparticle Subcommittee.

As the curator in charge, Philipp R. Heck oversees the collection of meteorites at the recently established Robert A. Pritzker Center for Meteoritics and Polar Studies, the largest meteorite collection housed at a private institution with more than 12000 specimens and more than 1600 different meteorites. Other responsibilities include the curation of the gem, mineral, rock and economic geology collections.


Philipp R. Heck came to the Field Museum in March 2010 from the University of Chicago, where he was a postdoctoral scholar working on new analytical techniques for presolar grains. He obtained his M.Sc. and Ph.D. degrees at ETH Zurich in Switzerland in geo- and cosmochemistry. He then worked as a postdoctoral fellow at the Max-Planck-Institute for Chemistry where he studied the first comet dust brought back from Comet Wild-2 by NASA’s Stardust Mission and at the University of Wisconsin-Madison where he worked mainly on fossil meteorites and banded iron formations from around the world. For his studies he uses specialized analytical techniques such as secondary ion mass spectrometry (NanoSIMS, IMS-1280 and TOF-SIMS), noble gas mass spectrometry, atom probe tomography, scanning electron microscopy and electron microprobe analysis. Sample preparation for atom-probe work is performed with focused ion beam workstations.