Goal 6: Understand the principles that will shape the future of life, both on Earth and beyond
Elucidate the drivers and effects of ecosystem change as a basis for projecting likely future changes on time scales ranging from decades to millions of years, and explore the potential for microbial life to adapt and evolve in environments beyond its planet of origin.
Life on Earth is based upon networks of biochemical reactions that interact with the crust, oceans and atmosphere to maintain a biosphere that has been remarkably resilient to environmental challenges. These networks of metabolic reactions developed within self-organized microbial ecosystems that collectively responded to environmental changes in ways that apparently stabilized the biosphere. Evolutionary biologists are working to understand how such biological and environmental processes have shaped specific ecosystems in Earth's history. However, it is far more difficult to employ such principles to formulate accurate predictions about the state of future ecosystems, especially when changes in planetary conditions are faster than the tempo of evolution. Predictions of this nature will require improved models of the biogeochemical cycling of critical elements, as these cycles represent the first-order interplay between the metabolic sequences of life and the surrounding physical world.
Viewing Earth's ecosystems in the context of astrobiology challenges us to consider how "resilient" life really is on a planetary scale, to develop mathematical representations of stabilizing feedbacks that permit the continuity of life in the face of rapidly changing physical conditions, and to understand the limits of these stabilizing feedbacks. Ideally, this consideration will provide insight into the potential impacts of physical changes at time scales ranging from seasonal and/or abrupt changes to changes that develop over millions of years.
The potential for microbial life to adapt and evolve in environments beyond its planet of origin should be assessed. Little is currently known regarding the consequences when earthly microbial life is transported into space or to other planets, where the environment is very different from that of Earth. The findings from such studies will determine whether life on Earth is strictly a local planetary phenomenon or can expand its evolutionary trajectory beyond its place of origin.
Humans are increasingly perturbing Earth's biogeochemical cycles. In addition to impacting the carbon cycle, humans have doubled the natural global sulfur emissions to the atmosphere, doubled the global rate of nitrogen fixation, enhanced levels of phosphorus loading to the ocean, altered the silica cycle, and perhaps, most critically, altered the hydrological cycle. Relative to many natural perturbations, the effects of human activities have been extremely rapid. Understanding how these changes will affect planetary climate, ecosystem structure, and human habitats is an urgent research priority in which astrobiology can play an important role.
A conceptual continuum embraces the development of biogeochemical cycles, the evolution to the modern biosphere and ongoing human effects. Studies of processes over long time scales (millenia to millions of years) offer an observational context that extends and strengthens the interpretation of shorter time scale (annual to century) phenomena. While longer-term changes in Earth's ecosystems are strongly affected by processes such as tectonics and evolution, the relatively rapid rates of recent change, influenced by anthropogenic forcing, may have analogues in previous important events such as major extinctions.
A key objective for elucidating the sign of the feedbacks in biogeochemical cycles and for understanding how the cycles respond to perturbations is to develop quantitative models that incorporate the interactions between metabolic and geochemical processes. For example, how are the key biogeochemical cycles of the light elements (e.g., C, N, O, S, P, etc.) related? What constrains these cycles on time scales of years to millions of years? How are these cycles altered by rapid changes in climate? Does functional redundancy, as indicated by a great diversity within microbial ecosystems, ensure ecosystem resilience? Are specific metabolic pathways more sensitive to perturbations than others? How have the biogeochemical cycles co-evolved with Earth on time scales of millions of years? Our vision of the future will be sharpened by a retrospective view offered by such a biogeochemical model that is verified by preserved records. This effort is needed in order to expand the current focus on short-term changes and "what is happening" in order to perform more hypothesis-testing and thus address "why this is happening."
Biota that are transported beyond their planet of origin perhaps experience the ultimate environmental perturbation, one that, in most, if not all, cases, challenges their very existence. Still, understanding survival and evolution beyond the planet of origin is essential for evaluating the potential for the interplanetary transfer of viable organisms and thus the potential that any life elsewhere in the Solar System might share a common origin with life on Earth. Conditions in space and on other worlds might, in some cases, be much more extreme than those encountered by any of the habitable extreme environments on Earth. Therefore, studies of survivorship beyond Earth are an ultimate test of the resilience of Earth-originated life and thus its potential for diversification far beyond the limits of our current understanding.
Conduct remote sensing, laboratory and field studies that relate the effects of environmental changes during Earth history to the cycling of key elements. Relate changes in elemental cycling to effects on the structure and functioning of organisms, populations, communities, and ecosystems. Develop predictive models that integrate biogeochemical cycles with biological evolution and environmental change (both anthropogenic and non-anthropogenic, including extraterrestrial events [see Objective 4.3]).
Explore the adaptation, survival and evolution of microbial life under environmental conditions that simulate conditions in space or on other potentially habitable planets. Insights into survival strategies will provide a basis for evaluating the potential for interplanetary transfer of viable microbes and also the requirements for effective planetary protection.