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From a distance, emerges from the cacti and creosote of the Sonoran desert like a gleaming oasis, a colony of glass and bright white structures. Despite being just outside Tucson, Arizona, it looks almost like a colony on another planet.

When one of the facility's 100,000 annual visitors steps inside, they see a whole world—from a tropical rainforest, glistening in 50 shades of green and teeming with life, to a miniature, experimental ocean. Toward the end of the tour, the visitor comes to a comparatively barren-looking experiment called the , where life is struggling to establish itself on crushed volcanic rock originally spewed from an ancient Arizonan volcano.

It is these rock slopes, where life is colonizing and transforming a tough landscape, that our team thinks are the key to humanity's future—both on Earth and, eventually, on other worlds.

Biosphere 2 first became famous as the that sealed a group of eight researchers inside its 3 acres of diverse ecosystems for two long years. The goal was to experiment with the viability of a closed ecological system to maintain human life in outer space. Today, we—a , an and a specializing in microbial biogeochemistry, along with our team of colleagues—have made Biosphere 2 into a test bed for understanding how life transforms landscapes, from local areas to whole planets.

We hope to use what we learn to help preserve , access to and . To address these issues, we must understand how soil, rocks, water and microbes together drive the transformation of landscapes, from local to planetary scales.

Beyond Earth, these same principles apply to the : the science of rendering other worlds habitable.

How life on Earth affects Earth

Life doesn't just sit on Earth's surface. Organisms profoundly affect the planet's geology, as well as the atmosphere's composition. Biology can transform barren environments into habitable ecosystems.

This happened with the , the first microscopic organisms to use oxygen-producing photosynthesis. Cyanobacteria pumped 2 billion to 3 billion years ago.

Atmospheric oxygen, in turn, enabled a new supercharged metabolism of life called aerobic, or oxygen-using, respiration. produced so much energy that it became the dominant way for organisms to make the energy needed for life, eventually making multicellular life possible.

In addition, the oxygen produced by photosynthesizing cyanobacteria also made its way to the upper atmosphere, forming another kind of oxygen , which, by shielding Earth's surface from sterilizing ultraviolet radiation, allowed life to expand onto land.

Biology again transformed the planet when the life that expanded onto land 400 million years ago gave a biological boost to the . Weathering occurs when carbon dioxide in the atmosphere chemically reacts with material on Earth's surface—such as rocks, minerals and water—to create soils imbued with nutrients that can support plants and other living organisms.

On Earth, weathering was first driven by purely physical and chemical processes. Once plants expanded from the oceans onto land, however, their roots injected carbon dioxide directly into the soil where weathering reactions were strongest. This process . Lower carbon dioxide levels in the atmosphere then cooled Earth, turning into one with a more temperate climate, like the one enjoyed by life today.

How organisms colonize new landscapes

When life colonizes a new, previously barren landscape, it starts up the process of . In this process, the first biological organisms—simple microbes—expand into interacting communities made of different kinds of organisms, which increase in complexity and biodiversity as they change and adapt to fit their new environment.

These microbes through photosynthesis and respiration to produce organic molecules called metabolites. The metabolites can alter the soil, allowing it to support larger plants. The larger plants that then emerge have complex structures such as roots and leaves that regulate the flow of water—and contribute to weathering. Eventually, humans can domesticate some of these plants for food crops.

Biosphere 2's Landscape Evolution Observatory is ideal for the careful study of how weathering and primary succession work together. Those processes both happen at the small, molecular scale but emerge as important only over large areas.

The Landscape Evolution Observatory has both hillslopes larger than any experiment in the world and crushed rock soils that are more simple and uniform than almost any natural setting. These characteristics mean the molecular measurements are consistent and understandable, even in different places across the larger hillslope.

The observatory is made up of three hillslopes covering 300 square yards that look like three giant tray-shaped, inclined planters made of steel, filled with crushed rock instead of fertile soil. The rain that falls on them soaks into the surface and flows down the incline to dribble out along the lower edge, where it is captured and carefully measured for its chemical and biological content.

We are using biological tools to understand how microbes and simple plants end up spreading across the larger, originally bare, crushed-rock hillslopes. These techniques include , which can identify all the microbial life forms in a hillslope, and , which can look at the organic molecules that microbes and plants produce and use in their interactions with each other and their surroundings.

Putting this all together, we see that colonies of photosynthesizing bacteria initiate succession on the Landscape Evolution Observatory. Critically, these cyanobacteria—descendants of those same organisms that gave Earth oxygen—capture the essential nutrient, nitrogen, from the air. Nitrogen buildup paves the way for mosses—simple plants without roots—to join them.

These bacteria-moss communities are now gradually spreading across the observatory's hillslopes, preparing the way for the next phase: colonization by larger plants with roots.

By learning how life establishes itself and then thrives on lifeless landscapes, we will gain insights for addressing key problems scientists face today. For example, when life-forms in a new landscape successfully spread and diversify, they tell us how biodiversity is preserved.

When those spreading organisms transform the way a landscape uses water, they give us lessons on how we should use water. And when plants find a way to be productive under stressful conditions, they give us examples for increasing our own plant-dependent food security.

Implications for Mars

Earth isn't the only planet where we can apply our findings. Today, Mars, unlike Earth, is a barren, . But it was once warmer, wetter and, like the early Earth, it may have several billion years ago.

While the rock in the Landscape Evolution Observatory comes from an Arizona volcano, basalt is the same kind of rock found on the surface of the moon and Mars.

Countries such as the and plan to land humans on Mars, and the company has grandiose plans to send a million colonists there. If humans ever hope to grow plants on the red planet's surface, learning how to create early succession there will prove crucial.

Before Mars colonization can happen at a large, sustainable scale, the first step is to grow plants and create food for human life. That is, we must solve what might be called the "Matt Damon problem," after the actor in the movie "The Martian." In order to survive, his character had to quickly learn to —potatoes—on Mars.

Matt Damon's character would probably not have survived on the real Mars of today, because its rocklike surface, , is too full of salts and for potatoes, or most Earth-like plants, to grow.

At the Landscape Evolution Observatory, we are focusing on experiments in chambers that simulate Martian environments to ask what it will take to detoxify Mars-like soils so that microbes and plants can live there.

One initial approach is to use , recruited from extreme environments on Earth, to convert the perchlorate into harmless chloride.

In this way, experiments at Biosphere 2 are informing the science of . Together with progress made in other areas, such as finding ways of , restoring barren environments on Earth could be a key to one day living on Mars.

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