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Executive Summary

Executive Summary — HAR (dm)

The Harvard NAI team was constituted in 1998 as an interactive group of biogeochemists, paleontologists, sedimentary geologists, geochemists, and tectonic geologists assembled with the common goal of understanding the coevolution of life and environments in Earth history. The team originally proposed to focus multidisplinary research on four critical intervals of planetary change: the early Archean (>3000 million years ago) when life began, the early Paleoproterozoic (2400-2200 Ma) when oxygen began to accumulate in the atmosphere and surface ocean, the terminal Proterozoic and Early Cambrian (750-525 Ma) when animal life radiated, and the Permo-Triassic boundary (251 Ma) when mass extinction removed some 90 percent of Earth’s species diversity, permanently altering the course of evolution. Given reduced funding levels in years 1 and 2, the team chose to focus on the latter three intervals. As documented in the accompanying project reports, we have made substantial new contributions to all three areas in funding year 3. At the same time, increased funding and strong interest by colleagues at Harvard and MIT have enabled us to expand both our membership and intellectual purview in year 3. In addition to the three projects funded from the outset (and approached in new ways by our newest co-investigators), we have three new projects underway. John Hayes’ research at the interface of microbiology and biogeochemistry has expanded as a result of incremental funding that enabled his group to undertake a substantial collaborative effort with the NAI Team at MBL. In association with the Spanish Center for Astrobiology, Andrew Knoll and Ariel Anbar have initiated research on Neogene iron formations in southern Spain that may illuminate both geobiological research on Earth’s ancient iron formations and NASA’s Mars lander mission slated for 2003 launch.

Research by the Harvard team is interdisciplinary, attracting increasing participation by scientists within the five member institutions (Harvard, MIT, WHOI, Rochester, Smithsonian Institution). We have also been successful in promoting cross-team collaborations — currently, individual research projects are underway with colleagues from the Carnegie, MBL, Ames, and JPL teams, as well as both the Spanish and Australian astrobiology centers. Moreover, our team participates actively in the Evogenomics Focus Group (C. Marshall) and has taken a leadership position in the “Mission to Early Earth” Focus Group (A. Anbar). Team members are active in research on novel biosignatures and digital mapping technologies that can be applied to solar system research. Field research is underway in Svalbard, Namibia, Newfoundland, Morocco, northern Australia, and China, with new projects planned for year 4. We also teach actively at four universities, contributing to both the training of new professionals and the education of a broader university community. Other outreach efforts focus on lectures presented by team members in a wide variety of public and professional formats.

Research highlights for the past year include the following:

â?¢ Mo isotopes have been shown to be potential paleoredox probes in ancient sedimentary rocks.

â?¢ Deep waters in a mid-Proterozoic basin have been shown to be sulfidic, consistent with models suggesting that the modern oxic deep ocean only came to exist near the end of the Proterozoic Eon.

â?¢ Newly discovered microfossils show that in 1500 Ma marine basins, eukaryotic algae were most abudnant and diverse in coastal environments; they expanded to become ecologically important throughout the oceans only toward the end of the Proterozoic Eon. Scarcity of critical nutrient metals in postulated sulfidic Proterozoic oceans may help to explain the observed ecological and stratigraphic distribution of eukaryotic algae in Proterozoic sedimentary rocks.

â?¢ Namacalathus, one of the earliest known biomineralizing animals, was reconstructed digitally using high-resolution serial sectioning. This permitted accurate assessment of the diversity, taxonomic relationships, and functional morphology of early skeleton-forming animals. Namacalathus and Cloudina were also discovered below and above a significant carbon-isotope excursion in Oman, interpreted as the Precambrian-Cambrian boundary biogeochemical event. This discovery indicates that these organisms did not go extinct at the boundary.

â?¢ A new model, based on carbon isotopic data, has been developed to explain the onset of Neoproterozoic Snowball Earth events.

â?¢ Elucidation of ecological and taphonomic processes that govern the formation and preservation of microbial mat signatures in ancient siliciclastic rocks provides new insights on a biosignature that is potentially applicable to Mars rover exploration.

â?¢ Combined field research in Newfoundland and laboratory analyses place new geochronological constraints on the timing and duration of late Neoproterozoic glaciation and its relationship to Ediacaran animal diversification.

â?¢ Field research in China and subsequent laboratory geochronology demonstrated that the end-Permian mass extinction was catastrophic, occurring in much less than 500 ky.

â?¢ Oceanographic modeling has been used to investigate proposed mechanisms for the end-Permian mass extinction. New models clarify spells out the conditions required to support a haline mode of circulation with sinking of brackish waters from the subtropics: haline modes are favored in climates that are warm, with weak pole-equator temperature gradients, enhanced hydrological cycles and supercontinents.

â?¢ A modification of standard electron microprobe technique allows micrometer-scale mapping of elements, including carbon, in fossils. This provides a non-destructive tool that will find use in microchemical analysis of samples returned from Mars and elsewhere.

â?¢ Team research has provided the first definitive and quantitative view of the sources of hydrogen used in biosyntheses of biomarker lipids. It thus provides vital information for the interpretation of hydrogen-isotopic compositions of organic compounds.

â?¢ Assembly and preliminary analysis of a new, comprehensive data base on the fossil record suggests that the large and continuing increase in diversity inferred for the past 250 million years could reflect geological and collecting biases as much as true evolutionary pattern.