Following the devastating Chicxulub asteroid impact, which occurred approximately 66 million years ago, a staggering three-quarters of Earth’s flora and fauna faced extinction.
This catastrophic event, most notably, led to the demise of all non-avian dinosaurs.
However, amidst the widespread destruction of plant and animal life, another kingdom of organisms found an opportune moment to thrive.
Adapted to decompose dead organic material and seemingly unaffected by the diminished sunlight and colder global temperatures, the fungi kingdom experienced a significant expansion.
Recent investigations of ancient geological strata in Colorado and North Dakota have uncovered compelling evidence of a pronounced surge in fungal activity immediately subsequent to the asteroid’s impact.
Similarly, rock formations in New Zealand from the same geological epoch exhibit analogous evidence of fungal proliferation in the post-Chicxulub era.
It is hypothesized by the authors of a recent study that this widespread fungal resurgence following the cataclysm may have been a global phenomenon.
Rosanna Baker and Arturo Casadevall, microbiologists affiliated with Johns Hopkins University, collaborated to interpret the prehistoric fungal fossil record, identifying three pivotal mycological periods surrounding the asteroid impact event.
These evidence of fungal proliferation were preserved within sedimentary rock layers found in Colorado’s Denver Basin and North Dakota’s Williston Basin.
Sedimentary rock, composed of accumulated silt and other particulates deposited over millennia and subsequently lithified, serves as a natural archive of Earth’s historical transformations, enabling paleontologists and geologists to reconstruct chronologies of past events.
Sedimentary rock formations globally contain a distinctive stratum marked by an elevated concentration of iridium, a geochemical signature significantly exceeding levels observed in other geological periods.
This notable layer, recognized as the Cretaceous–Paleogene (K–Pg) boundary, formed 66 million years ago, and is widely attributed to the Chicxulub impact event that imprinted this unique marker.
Both the North Dakota and Colorado rock samples clearly display this boundary layer.
“Our analysis defined a fungal spike as a condition where fungal spores constituted 50% or more of the total fungal and plant spore count,” Baker informed ScienceAlert.
“Consequently, as plant life eventually regenerated, the equilibrium shifted back to a state where plant spores predominated over fungal spores.”
Within the Colorado sample, an profusion of fungal spores and hyphae, manifesting in diverse forms and sizes, are observable adjacent to the K-Pg boundary, embedded directly within this geological interface.
In the strata deposited between 2,000 and 10,000 years following the K–Pg boundary, evidence points to an extended period of fungal proliferation, as the mycelial networks expanded within the cool, damp conditions that followed the mass extinction event.
However, the asteroid was not the sole instigator of this fungal surge.
An earlier geological event left a similar imprint in the rock record: the Deccan Traps volcanic eruptions. These eruptions, which spanned the K-Pg boundary, were historically considered the primary cause of the mass extinction.
This preceding fungal proliferation, dated approximately between 30,000 and 10,000 years before the Chicxulub impact, coincides with a cooler climatic period and is “intriguingly coincident” with a particularly vigorous phase of the Deccan Traps’ eruptive activity, as indicated by research data.
Fungi generally favor cooler temperatures and more acidic environments. It is plausible that the cooler and dimmer atmospheric conditions, brought about by geological events (or even anthropogenic ones) that obscure the sky—as was undoubtedly the case with Chicxulub and the Deccan Traps eruptions—could foster an extensive fungal bloom.
“We interpret the fungal bloom that occurred prior to the impact as indicative that the intense and protracted volcanic activity during the late Cretaceous was imposing significant stress on the planet before the arrival of the meteorite,” Baker stated.
Casadevall further posited that the Cretaceous extinction may have been a consequence of a “two-stage impact involving volcanism and a bolide strike,” rather than a singular triggering event.
Additional research is requisite to precisely categorize these prehistoric fungal remnants—spores and hyphal fragments—within their extant phylogenetic groups, determining if they represent molds, mushrooms, or other fungal classifications.
Nevertheless, Baker and Casadevall hypothesize that the successful fungal species were likely saprotrophs, organisms that derive nourishment from decomposing organic matter, thereby facilitating the gradual breakdown of the abundant organic material left behind by flora and fauna adversely affected by the extinction event.
Current understanding confirms that these fungi belonged to the phylum Ascomycota. Their more widely recognized contemporary relatives include species like morels, truffles, baker’s yeast, and cup fungi.
The dimensions of the spores found within the K-Pg boundary layer, in particular, are comparable to those of well-nourished saprotrophs, while the smaller spores detected in the preceding and subsequent spikes are characteristic of fungi adapted to leaner, colder, and more acidic conditions, exhibiting resilience during periods of environmental stress.
These spores were notably rich in melanin, a pigment recognized for its protective properties against the deleterious effects of radiation, acting, as Baker aptly describes it, “like a suit of armor.”
“When considered in conjunction with documented instances of fungal expansion following prior global calamities, these findings suggest that fungi possess a remarkable capacity to flourish in the aftermath of widespread ecological collapse,” Baker and Casadevall noted in their publication.
“Given the potential for fungi to induce pathology in both plant and animal kingdoms, the occurrence of fungal proliferation events carries significant implications for the recovery trajectories of species persisting through global cataclysms.”
Through their proliferation in disaster’s wake, these fungi likely played a crucial role in the decomposition and recycling of detritus, thereby establishing the foundation for the subsequent resurgence and diversification of complex life on Earth.
Evidently, no task appears to be beyond the scope of nature’s indispensable recycling agents.
