At first look, the grit crust might look like a routine instance of what researchers name a organic soil crust, or “biocrust”—a neighborhood of coexisting micro organism, fungi, algae, and different microorganisms that caps the soil in coherent sheets. Around 12 p.c of Earth’s land is roofed by biocrusts. Ecologists usually refer to those colonies as the planet’s “living skin.”
Over the final century, scientists have recognized biocrusts round the globe and labored to grasp their function in shaping ecosystems. They’ve realized that the crusts anchor soil grains in place and supply the organisms rising in that soil with important vitamins akin to carbon, nitrogen and phosphorus. In 2012, Büdel and his colleagues estimated that biocrusts take in and recycle round 7 p.c of all the carbon and almost half of all the nitrogen that’s chemically “fixed” by terrestrial vegetation. The function of the biocrusts in procuring digestible nitrogen is especially vital in arid deserts: Elsewhere, lightning can usually convert atmospheric nitrogen to nitrates, however in the deserts, electrical storms are uncommon.
The biocrust creates “little oases of fertility,” mentioned Jayne Belnap, an ecologist at the U.S. Geological Survey who helped to standardize the time period “biocrust” in 2001. “That area is going to be [like] popsicles for the soil organisms. They’re sugar addicts just like all the rest of us.”
But the microbial neighborhood in Pan de Azúcar isn’t simply any previous biocrust. While conventional biocrusts drape themselves over the prime layer of positive soil particles, and different kinds of organisms sprout immediately on prime of particular person boulders, “the grit is in between—it’s a transition zone,” mentioned Liesbeth van den Brink, an ecology researcher at the University of Tübingen who now lives simply outdoors Pan de Azúcar with Gutiérrez Alvarado. In grit crust, the stones present the construction, however the microbes colonize them in a coherent sheet—like a skinny layer of resin grouting collectively a rock backyard.
Because the organisms are so intimately related to the rocky substrate, the grit crusts embody “the collision of the abiotic with the biotic,” mentioned Rómulo Oses, a biologist at the University of Atacama. “At this interface, you will see a lot of answers.”
The grit crusts of Pan de Azúcar have compelled scientists to develop their conception of what biocrusts are, the place microbes can survive, and the way microbial communities form the setting round them. They are opening the door for reconsiderations of how Earth and life coevolved over epochs.
In the park, numerous species of cactus are nourished by a fog that usually seeps in from the coast.Photograph: Zack Savitsky/Quanta Magazine
Sipping on Fog
Pan de Azúcar is desolate, nevertheless it’s removed from lifeless. Bordering the Pacific Ocean close to sea degree, the park is rather more temperate than the Atacama’s elevated hyper-arid core. Still, it receives at most 12 millimeters of rain per 12 months, and the photo voltaic radiation ranges are sometimes blisteringly excessive.
On the solution to the park’s sole meals truck, the place Gutiérrez Alvarado, van den Brink, and I can cease for a native seafood empanada, we take a detour. Gutiérrez Alvarado stops to examine on one in every of his weather-monitoring gadgets, which is enclosed in barbed wire and mounted down with rocks in the desert. Next to it, he factors out a roughly cow-size melancholy in the floor the place a guanaco, a wild relative of the llama, lately took a mud tub. Gutiérrez Alvarado and the different rangers lately counted 83 guanacos dwelling in the park.