At first glance, the grit crust could appear to be a routine example of what researchers call a biological soil crust, or “biocrust”—a community of coexisting bacteria, fungi, algae, and other microorganisms that caps the soil in coherent sheets. Around 12 percent of Earth’s land is roofed by biocrusts. Ecologists often discuss with these colonies because the planet’s “living skin.”
Over the last century, scientists have identified biocrusts across the globe and worked to know their role in shaping ecosystems. They’ve learned that the crusts anchor soil grains in place and supply the organisms growing in that soil with essential nutrients resembling carbon, nitrogen and phosphorus. In 2012, Büdel and his colleagues estimated that biocrusts absorb and recycle around 7 percent of all of the carbon and nearly half of all of the nitrogen that’s chemically “fixed” by terrestrial vegetation. The role of the biocrusts in procuring digestible nitrogen is especially critical in arid deserts: Elsewhere, lightning can often convert atmospheric nitrogen to nitrates, but within the deserts, electrical storms are rare.
The biocrust creates “little oases of fertility,” said Jayne Belnap, an ecologist on the U.S. Geological Survey who helped to standardize the term “biocrust” in 2001. “That area goes to be [like] popsicles for the soil organisms. They’re sugar addicts identical to all the remaining of us.”
But the microbial community in Pan de Azúcar isn’t just any old biocrust. While traditional biocrusts drape themselves excessive layer of superb soil particles, and different kinds of organisms sprout directly on top of individual boulders, “the grit is in between—it’s a transition zone,” said Liesbeth van den Brink, an ecology researcher on the University of Tübingen who now lives just outside Pan de Azúcar with Gutiérrez Alvarado. In grit crust, the stones provide the structure, however the microbes colonize them in a coherent sheet—like a skinny layer of resin grouting together a rock garden.
Because the organisms are so intimately related to the rocky substrate, the grit crusts embody “the collision of the abiotic with the biotic,” said Rómulo Oses, a biologist on the University of Atacama. “At this interface, you will note a number of answers.”
The grit crusts of Pan de Azúcar have compelled scientists to expand their conception of what biocrusts are, where microbes can survive, and the way microbial communities shape the environment around them. They are opening the door for reconsiderations of how Earth and life coevolved over epochs.
In the park, various species of cactus are nourished by a fog that commonly seeps in from the coast.Photograph: Zack Savitsky/Quanta Magazine
Sipping on Fog
Pan de Azúcar is desolate, but it surely’s removed from lifeless. Bordering the Pacific Ocean near sea level, the park is rather more temperate than the Atacama’s elevated hyper-arid core. Still, it receives at most 12 millimeters of rain per yr, and the solar radiation levels are sometimes blisteringly high.
On the strategy to the park’s sole food truck, where Gutiérrez Alvarado, van den Brink, and I can stop for an area seafood empanada, we take a detour. Gutiérrez Alvarado stops to examine on one in all his weather-monitoring devices, which is enclosed in barbed wire and fastened down with rocks within the desert. Next to it, he points out a roughly cow-size depression in the bottom where a guanaco, a wild relative of the llama, recently took a dust bath. Gutiérrez Alvarado and the opposite rangers recently counted 83 guanacos living within the park.
