Approximately 66 million years ago, the catastrophic Chicxulub asteroid impact led to the extinction of three-quarters of Earth’s plant and animal species, including all non-avian dinosaurs. Amidst this devastation, the fungi kingdom found an opportunity to thrive, undeterred by the dimmed sunlight and cooler climate. This period saw fungi flourish by decomposing the remains of other organisms.
Recent findings from ancient rock layers in Colorado and North Dakota reveal a significant increase in fungal activity immediately following the asteroid’s impact. This is mirrored in New Zealand’s geological records from the same era, suggesting that this fungal flourishing might have been a global phenomenon.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>Microbiologists Rosanna Baker and Arturo Casadevall from Johns Hopkins University have examined the prehistoric fungal fossil record, identifying three significant mycological events around the time of the asteroid impact. Evidence of these events is found in sedimentary rock layers in Colorado’s Denver Basin and North Dakota’s Williston Basin.
Sedimentary rocks consist of layers of silt and materials compressed over time, preserving a natural record of Earth’s changes through the ages. A distinctive layer of iridium, a marker of the Cretaceous–Paleogene (K–Pg) boundary, formed 66 million years ago, is present in these rocks, confirming the Chicxulub impact.
Baker explained to ScienceAlert, “In our analysis, a fungal spike was defined as 50 percent or more fungal spores out of the total fungal and plant spores.” This balance shifted back to plant spores as plant life recovered.
The Colorado samples show a rich variety of fungal spores and hyphae near the K-Pg line. In layers dating 2,000 to 10,000 years after the boundary, there is evidence of prolonged fungal growth in the cold, damp environment following the mass extinction.
The Chicxulub impact was not the sole catalyst for this fungal rise. Earlier, the Deccan Traps volcanic eruptions, spanning the K-Pg boundary, left a similar signature in rocks. This earlier fungal spike, occurring 30,000 to 10,000 years before the asteroid impact, coincides with cooler climate periods and a notable phase of Deccan activity.
Fungi favor cooler, acidic conditions, and it appears that the darker, cooler environments created by events like the Chicxulub impact and the Deccan eruptions set the stage for widespread fungal proliferation.
Baker noted, “We think the fungal bloom that occurred before the impact is evidence that the intense and prolonged period of volcanic activity in the late Cretaceous was stressing the planet before the meteorite impact.” Casadevall added that the Cretaceous extinction might have been a “two-punch hit by volcanism and a bolide” rather than a single event.
Further research is necessary to identify these prehistoric fungi’s living relatives, whether they were molds, mushrooms, or other types. Baker and Casadevall suspect that the thriving fungi were likely saprotrophs, which feed on decaying matter, breaking down the organic material left by extinct plants and animals.
The extinct fungi belonged to the Ascomycota phylum, relatives of morels, truffles, baker’s yeast, and cup fungi. Their spores, found in the K-Pg boundary layer, resemble well-fed saprotrophs, while smaller spores from earlier and later spikes suggest leaner, cold- and acid-adapted fungi.
The spores were rich in melanin, which protects fungi from radiation, acting “like a suit of armor,” according to Baker.
Related: Hotter Climate Could Fuel Spread of Dangerous Fungi, Scientists Warn
Baker and Casadevall write, “Taken together with reports of fungal expansion following prior global calamities, these findings indicate that fungi can often flourish in the aftermath of ecosystem-level collapse.” They caution that fungal proliferation events could impact the recovery of surviving plant and animal species after global disasters.
By thriving in the post-disaster period, these fungi likely played a crucial role in recycling organic material, paving the way for the resurgence of complex life on Earth.
The research was published in PNAS.
