Strong reasons exist to hypothesize that phyllosilicates, that is, clay minerals, played a critical catalytic role in the organic synthesis of prebiotic and possibly early biotic compounds and structures. Phyllosilicates would be expected to be abundant at the surface of early Earth (the Hadean) by the hydrous alteration of impact-generated silicate debris. The explorations of Earth, the Moon, and Mars permit reasonable inferences about physical conditions on prebiotic Earth. Also, currently available information allows the definition of necessary steps in prebiotic synthesis in which phyllosilicates may have participated. Consideration of these steps supports the plausibility that such minerals provided catalytic, substrate, and organizational functions for prebiotic and possibly early biotic development of organic structures, leading to formation and replication of ribonucleic acid (RNA) and, in turn, leading to a prebiotic RNA world. Ultimately, prokaryote cells may owe some of their functions to the inherent characteristics of associated phyllosilicates.

Paleontology has undergone a renaissance in the past 50 years, expanding from an empirical field focused on stratigraphic context to the theoretically grounded discipline of paleobiology. This transformation has been propelled by conceptual advances in two broadly construed areas, evolution and paleoecology. Phylogenetic systematics has revised our understanding of the evolutionary relationships among organisms. New understanding of tempo and mode in evolution, evolutionary hierarchies, the role of mass extinctions and recoveries, and developmental evolution has led to unexpected insights on evolutionary processes. Within paleoecology, taphonomy has led to greater understanding of the nature of the fossil record. Evolutionary paleoecologists have unearthed temporal and spatial patterns, at various scales, in diversity and community organization and have investigated the processes responsible for them. Other advances in paleoecology involve trace fossils; paleobiogeography; novel uses of fossils in understanding the environment; and the new discipline of conservation paleobiology. New concepts have been furthered by incorporating tools from other disciplines, including quantitative analytical methods, biostratigraphic innovations, geochemical and molecular tools, and advanced microscopy techniques. Fueling these advances are fossil discoveries revealing previously unknown Archean-Proterozoic worlds, detailed accounts of the explosion of life in the Cambrian, and floras and faunas yielding surprising and unexpected insights into the origins and evolution of important plant and animal groups.

Science has achieved tremendous success over the centuries, partly because the complexities of the Earth, the physical processes that sustain the planet, and the enormity of life were separated into disparate fields of study—mathematics, physics, chemistry, biology, and geology, to name only a few. Scientific compartmentalization was initially necessary to impart enough focus to make progress on complicated issues. However, as the knowledge base grew, it became more and more difficult to separate life and the history of the Earth, and vice versa. We now understand that to investigate the Earth's surface as an abiologic system is folly: Life and Earth processes are intimately linked. Hence, a new field was born at the interface between biology and geology: geobiology. As a field, geobiology seeks to understand the intersection of life and the rock record across Earth's history: how organisms influence the physical Earth and vice versa, and how the marriage of physical and biological processes have transformed our planet over its long history. The assessment of life's macromolecules of DNA, RNA, polysaccharides, proteins, and lipids, and their potential recalcitrance in an ecosystem, has opened up the field of geobiology to lead us toward a solid explanation of where life came from, how life has altered the planet, what may be possible for life elsewhere, and what represents one of the reasons for the explosion of geobiologic studies today. Here we outline how molecular biology has transformed our understanding of geobiology, describing a few of the essentials needed to understand geobiology and exploring an example of a modern geobiologically relevant system: a living stromatolite from the shore of a geothermal hot spring in Yellowstone National Park, Wyoming, USA.

Discoveries in geobiology have dramatically shaped our understanding of the nature, distribution, and evolutionary potential of terrestrial life, paving the way for new exploration strategies to search for life elsewhere in the Solar System. Genomic studies, applied over a broad range of geological environments, have revealed that the vast proportion of species on Earth are microbial. Studies of the fossil record indicate that this has been the case for >75% of our planet's history. Microbial life has been shown to occupy a stunning array of environmental extremes, seemingly only limited by the distribution of liquid water and its chemical activity, nutrient availability, suitable energy sources, radiation, etc. Advances in geomicrobiology have revealed important contributions of microbial processes to many global biogeochemical cycles, and in the evolution of Earth's atmospheric and surface composition. The discovery of a subsurface biosphere, fueled by inorganic chemical energy and able to tolerate extremes in temperature and salinity, has been especially important in opening up new horizons for the astrobiological exploration of Mars, as well as icy satellites of the outer Solar System. Although the environment of life's origin remains uncertain, molecular studies suggest that the last common ancestor of life probably lived in hydrothermal environments where it utilized simple compounds of carbon, hydrogen, and sulfur as sources of chemical energy. This general view is consistent with what we know about late Hadean to early Archean environments on the Earth, as well as model-based interpretations of late, giant impacts that could have exterminated early mesophilic (and possibly photosynthetic) surface life forms, leaving behind only deep subsurface chemotrophic thermophilic microbial communities to re-populate the biosphere. These and related discoveries have contributed extensively to the view that life could be much more broadly distributed, within the Solar System and beyond, than once thought. We now believe it possible that life may have become established in surface environments on Mars during the first half billion years of the planet's history, when liquid water was widespread there. Furthermore, a subsurface hydrosphere on Mars (suggested by both models and geomorphic evidence) may have provided a continuously habitable zone for life over most of Martian history and could still support an active, deep biosphere on Mars today. Exploration of the outer Solar System supports the presence of saline brines (perhaps oceans) beneath the icy crusts of Europa, Callisto, and possibly Ganymede, along with plausible energy sources for life based on chemical disequilibria between oxidized and reduced compounds. It also appears that interior zones of liquid water may also exist on Enceladus, a moon of Saturn, while hydrocarbon oceans of liquid methane discovered on Titan may provide alternative solvents for novel life forms completely unlike anything found on Earth. Ongoing efforts to systematically explore potentially habitable environments elsewhere in our Solar System have helped catalyze the development of astrobiology, an emerging interdisciplinary science that seeks to understand the origin, evolution, distribution, and future of life in the cosmos. Geobiology, which studies interactions of biological and physical-chemical systems and how they have evolved over the history of Earth, is a central focus of astrobiology, providing fertile ground for the growth of conceptual models and new technological tools needed to implement the search for extraterrestrial life elsewhere in the Solar System.