Their days were numbered, all manner of Cretaceous life in kingdom plantae and animalia. Those that survived the impact winter became our modern groups of terrestrial and aquatic plants, animals, and marine plankton. Scientists want to understand how the Chicxulub asteroid that hit Earth 66 million years ago changed the conditions for life on the planet and veiled the sun for so many years, leading to the extinction of the dinosaurs. Secrets to this understanding are locked in the asteroid’s physical composition. An international research group has now produced a unique elemental map of the spherules formed by the asteroid impact, with data from MAX IV’s Balder and NanoMAX beamlines. The findings may better explain the aerosol cloud formation that catalysed extinction-level climate change.
The Chicxulub asteroid impact in the Gulf of Mexico, known as the Cretaceous–Paleogene (K–Pg) boundary event, marks the epoch demarcation, and the 5th mass extinction in the geological record. The asteroid carved a 200 kilometre-wide, kilometre-deep crater, globally dispersing a clay sediment layer abundant in platinum group elements (PGEs), namely iridium, osmium, and platinum. The ejected molten debris from the vaporized asteroid was preserved in the sediment as glass-like pearls called microspherules.
Major questions have remained about the spherule composition and chemical information, possible carrier elements of the idium in the spherules, and processes that occurred during global distribution after impact. To address these open questions, scientists from Sweden, Colombia, the U.S.A., and United Kingdom investigated spherules from Gorgonilla Island off the west coast of Colombia.
“We were surprised to find such a major heterogeneity, with that I mean that the composition of one spherule from another, is very different, with silica and calcium dominating in some, while others are full of iron. However, the major surprise was finding the elements that we were searching for, the rare iridium,” said Vivi Vajda, Professor of Palaeontology and Head of the Paleobiology department at the Swedish Museum of Natural History. “With the super-high-resolution mapping at NanoMAX, we could see the iridium in the form of tiny shards, in shapes of needles and triangles.”
Structural data collected from the spherules included use of X-ray fluorescence (XRF) microscopy at NanoMAX beamline and X-ray absorption spectroscopy (XAS) and X-ray absorption near edge structure (XANES) at Balder beamline at MAX IV. Results revealed the presence of PGEs and identified metallic carrier elements such as cobalt, nickel, lead and others. “We have been able to resolve a major enigma showing that iridium most likely has been transported in a mineral with copper and zinc, possibly minerals new to science,” explained Vajda.
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Image: Illustration of Chicxulub asteroid impact in the shallow tropical sea in what´s today the Mexican Gulf. The mixture of target rock, marine plankton, and the asteroid formed a melt that produced droplets which cooled to silica ‘pearls’ enclosing traces of the asteroid.
Credit: Pollyanna von Knorring