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Executive Summary

Oxygenation of Earth’s atmosphere and surface oceans over the interval c. 800 to c. 540 million years ago is widely considered to have been a critical environmental driver for the appearance and diversification of animal life. Further, understanding the interconnections between atmosphere-ocean oxygenation, anomalies in the biogeochemical carbon cycle, and planetary-scale glaciations remain one of the great puzzles in the history of life on Earth. Accordingly, in this reporting period members of the MIT Team of the NAI continued their study of the Neoproterozoic rock record for chemical evidence of ocean oxygenation and corresponding paleontological and paleoenvironmental data concerning the state of biological complexity. Collaborations between team members Tanja Bosak, Francis Macdonald, Phoebe Cohen, David Johnston and Samuel Bowring has explored the timescales, geochemical trends and microfossil diversity just prior to and during the early stages of the Cryogenian Period. The Cryogenian does not appear to be a biologically impoverished time but, instead, contains a rich record of complex microscopic protists. Their ecological relationships immediately before and after the initial Snowball Earth event, also known as the Sturtian glaciation, appear to be similar, and biotic recovery appears to have occurred within <20 kyr after the deglaciation. In other words, environmental conditions during the glaciation may not have significantly challenged the biota of that time.

The Ediacara biota, which appear immediately after the Cryogenian Period, are an enigmatic group of soft-bodied, probably metazoan organisms that flourished in the coastal oceans some 578-542 million years ago. These exquisite and distinctive fossils have a worldwide distribution; some of the most remarkable specimens found in the Mistaken Point Ecological Reserve on the southeastern coast of Newfoundland, Canada. Here, Ediacaran fossils are preserved as a complete census populations, allowing scientists to apply modern ecological analyses. Ecological and morphometric studies by members of the NAI team investigated the likelihood that some of these organisms actually represent the oldest body fossils of sponges. Complementary research conducted in a new collaboration with Marco Ghisalberti of the University of Western Australia suggests that the rangeomorphs of Mistaken Point (frond-like fossils with a ‘fractal’ structure) formed communities that comprised of 2 or 3 canopies each experiencing different fluid flow regimes, thereby taking advantage of shear forces to maximize access to nutrients and oxygen in the water column. Their results provide quantitative support for the ecological tiering model of Nabonne and Clapham (2002).

Other paleontological and geochemical studies are underway in sedimentary sequences across Northwestern Canada to elucidate events just prior to the Cryogenian Period. A study of organic matter in the Coppercap Formation in the Coates Lake Group of the MacKenzie Mountains, for example, has revealed evidence for an exceptionally euxinic setting that enabled both green and purple sulfur bacteria to flourish. The isotopic compositions of bulk organic and inorganic carbon in the Coates Lake co-vary through an extreme negative excursion suggesting that these are, in fact, recording a carbon cycle anomaly as opposed to diagenetic overprinting. Work planned for the coming year is aimed at determining if this is a localized event or one of regional or global extent, and at understanding how the composition of organic matter evolved through such an isotopic ‘excursion’. Concomitant strontium isotope studies being conducted in the Bowring lab will allow a through testing of the Derry (2010) hypothesis positing that the Neoproterozoic isotope excursions are an artifact of isotopic overprinting by petroliferous brines.

Caltech graduate student Magdalena Osburn, working with John Grotzinger in the Neoproterozoic terrains of Oman, is studying the transition from the Ediacaran Khufai to Shuram Formation to understand the inception of another distinctive geochemical phenomenon, the controversial Shuram carbon isotopic anomaly, one of the largest known deviations in Earth history. This work is aimed at testing of three primary hypotheses for its origin including the prevailing idea that it represents a major disruption to the biogeochemical carbon cycle. Complementing this research, Rothman’s group has been developing models to understand the ways in which Earth’s carbon cycle would be perturbed during transitions from low oxygen states to ones of high oxygen concentrations. Carbon isotopic patterns that are evident at the end of the Permian Period, and which culminate in the largest known mass extinction, are very similar to those in some Neoproterozoic sections, adding to other forms of evidence that similar processes were at work during these major events in Earth’s history.

Ann Pearson’s group has conducted studies of nitrogen isotopic relationships between bulk organic nitrogen and chlorophylls in photosynthetic algae and bacteria together with the N-isotopic variability during a major redox transition of the Cretaceous period where we can be confident that the sedimentary record is very well preserved. They confirmed that extreme negative excursions in the nitrogen isotopic composition of organic matter are an indicator of deep ocean redox conditions (as previously observed in sediments deposited at the end of the Permian) and, so long as sediments for study are chosen carefully, can reveal the state of global redox balance and the nitrogen cycle. Complementary work by Amy Kelly working in the Summons laboratory to look at the carbon isotopic compositions of individual hydrocarbons has confirmed observations and an hypothesis published over 15 years ago (Logan et al., 1995), but not studied to any significant extent since, that acetogenic and isoprenoidal lipids show isotopic patterns that switch systematically at the close of the Neoproterozoic Era. Modeling by Hilary Close working in Pearson’s laboratory has led to a new hypothesis counter to that of Logan and co-workers and attributes the observed pattern seen at the Neoproterozoic-Cambrian transition to the rise of the eukaryotic phytoplankton.

Andy Knoll completed a longstanding investigation on the comparative biology and paleobiology of complex multicellularity. Simple multicellularity has evolved numerous times within the Eukarya, but complex multicellular organisms belong to only six clades: animals, embryophytic land plants, florideophyte red algae, laminarialean brown algae, and two groups of fungi. Phylogeny and genomics suggest a generalized trajectory for the evolution of complex multicellularity, beginning with the cooption of existing genes for adhesion. This years’ research activity also targeted the evolution of biomineralization in early eukaryotes and, together with Caltech Postdoctoral fellow Jonathan Wilson, Knoll was able to show that early seed plants evolved a structural and functional diversity of xylem architectures broader, in some ways, than the range observable in living plants. Doug Erwin has continued work on the evolution of developmental gene regulatory networks in early metazoans and, with Jim Valentine (UC Berkeley) completed a manuscript on the Ediacaran-Cambrian diversification of animals.

The book synthesizes current understanding of the geological context, phylogenetic relationships, fossil record, paleoecology, and comparative developmental biology of the animal radiation. Erwin and Valentine argue that this event reflected a complex set of causes including a key positive feedback process whereby early metazoans modified their environment in their favor.

Members of the King laboratory continued their focus of the genomic underpinnings of the animal radiation by comparing animal genomes with genomes from their closest living unicellular relatives, the choanoflagellates. A key goal of this work is to reconstruct the genomic attributes of the last common ancestor of animals. Previously sequenced genomes from the choanoflagellates Monosiga brevicollis and Salpingoeca rosetta are now being complemented by three more from the choanoflagellates Salpingoeca napiformis, Diaphanoeca grandis and a homoscleromorph sponge Oscarella carmela. Key findings include the discovery of 56 protein domains in choanoflagellates that were previously thought to be specific to animals. Second, they have increased the number of protein domains inferred to be present in the common ancestor of choanoflagellates and animals by 50%, from the 112 domains previously found in M. brevicollis and S. rosetta to 168 domains. Third, many of these newly discovered protein domains represent key animal development and signaling pathways not previously observed outside of animals. A case in point is their study of the ancestry of the hedgehog signaling pathway. The hedgehog protein, a key regulator of developmental patterning in bilaterian animals, signals through the primary cilium, which is equivalent to the choanoflagellate flagellum. King and colleagues have also identified core components of the hedgehog signaling pathway in the choanoflagellate M. brevicollis that were previously known only from animals. Further important insights into the ancestral complexity and assembly of the Hedgehog signaling pathway are also emerging from the genome sequences of S. rosetta and O. carmela.

King’s work is strongly complemented by that of Kevin Peterson and his colleagues who employ molecular approaches to properly place animals like sponges and jellyfish into the tree of life. They have taken a multi-faceted approach using two different kinds of molecular data: traditional sequence-based molecular phylogenetics, and a new type of binary data, the presence or absence of specific microRNAs (short ~22 nucleotide non-coding RNA genes) to construct and verify the robustness of phylogenetic trems of the animal kingdom. Both data sets suggest that sponges are paraphyletic: some sponges are more closely related to jellyfish and humans than they are to other sponges (e.g., bath sponges). These results suggest that the last common ancestor of all living animals was organized like a true sponge, and thus our origins as complex animals lies within sponge biology.

Animals interact with the world through complex sensory structures such as eyes, ears, and antennae and these are coordinated by collections of neurons. While the nervous and sensory systems of animals are incredibly diverse, a growing body of evidence suggests that many of these systems are controlled by similar sets of genes. Members of the Jacobs laboratory are examining early branching lineages, represented by the jellyfish Aurelia and the worm Neanthes, of the animal family tree to see if these organisms use similar genes during neurosensory development as the better-studied fruit fly and mouse. This research is critical for determining which structures are shared between animals due to common ancestry and those that evolved independently in different lineages. Ultimately, such research informs how morphologically and behaviorally complex animals evolve. During the 2009-2010 period members of the Jacobs laboratory published research on the expression of two classes of genes necessary for the development of Aurelia sensory organization (Nakanishi et al 2010) and two papers on the neural organization and developmental gene expression, respectively, of Neanthes appendage development (Winchell et al a,b, 2010). Their studies suggest that sensory organ development in Aurelia is homologous to those of more complex bilaterian animals but also that canonical “limb” genes in Neanthes are not homologous with genes for appendages across bilaterians. Rather, their work points to a possible relationship between the evolution of appendages and sensory structures.

The transition from the microbial world to one with animals also involved complex metabolic innovations. Members of the Segre group use mathematical and computational approaches to study the dynamics and evolution of metabolism in individual microbes and in microbial ecosystems. In particular, they take advantage of sequenced genomes to study the complete network of biochemical reactions present in an organism. The have been extending these approaches from single genomes to multiple genomes, generating ecosystem-level models of metabolism which can, in turn, help us understand important aspects of the new ecology that developed as animal life blossomed.

Many members of the MIT are involved in the search for habitable environments beyond the Earth. The recent discovery of several potentially habitable Super-Earths, that is planets up to about 10x the mass of our own Earth that could be rocky, and the first nearby super-Earth planets around the habitable Zone of Gl581, has proven that we can already detect potentially habitable planets and makes this research extremely relevant. Dimitar Sasselov and Lisa Kaltenegger model atmospheric spectral signatures, including biosignatures, of known and hypothetical exoplanets that are potentially habitable. The atmospheric characterization of such Super-Earths and potentially habitable Moons, will allow us to explore the conditions on the first detectable rocky exoplanets and potentially characterize the first detectable habitable exoplanet.

In 2010, team members John Grotzinger and Andrew Knoll continued to work as members of the Mars MER science team. The rover Opportunity completed its investigation of Burn formation outcrop along the inner margin of Victoria crater and headed south toward new, potentially clay-rich targets around Endeavour crater. Opportunity’s progress and scientific discoveries during this period are summarized in a forthcoming paper by Arvidson et al. (2010). In related research, Andrew Knoll continued his longstanding collaboration with members of the Spanish center for Astrobiology. Combined field and laboratory analyses of the Rio Tinto ecosystem yielded a better understanding of how morphological and chemical signatures of life can be preserved in oxic, acidic settings like those at Meridiani planum, Mars (Fernandez-Remolar and Knoll, 2010).

Caltech team member John Grotzinger is the Project Scientist for The Mars Science Laboratory (MSL), a mission with the overall scientific goal of “exploring and quantitatively assessing a local region on Mars as a potential habitat for life, past or present” (http://msl-scicorner.jpl.nasa.gov/ScienceGoals/). A habitable environment is “one that has not only water, but also a source of carbon to make organism metabolism possible, and a source of energy to fuel that organism metabolism” (Grotzinger, 2009). MSL will search for organic carbon in rocks, soils, and the atmosphere, as well as the mineralogical diversity of the rock and soil chemistry. John, together with staff scientist Jennifer Griffes and graduate student Katie Stack have all been working on landing site analysis for MSL. They are part of the larger Landing Site Working Group, a major effort for assessing potential geologic targets for each site, mapping regions of interest, identifying and compiling hypotheses for the science targets, and developing plans that would test these hypotheses, including possible traverses. These assessments will be done using criteria that include diversity, context, habitability and preservation for each site.

The diverse and innovative scientific research that has taken place in our group this year has been accompanied by renewed efforts by our education and outreach team. The hire and energy of Dr. Phoebe Cohen, our new Education and Outreach Coordinator, has led to exciting new directions in our E/PO plan. We are using web and social media outlets, including twitter, facebook, a youtube video series, and our website, to distribute information about our research and our team members to the public. We have undertaken concerted work on two complimentary web-based educational modules, one for middle school audiences, and one for the college level, to help to communicate the science that we do to students worldwide. Through lectures, presentations, and workshops, the PI’s on our team, most notably Lisa Kaltenegger, reach hundreds of students and members of the general public throughout the year. In one particularly significant effort, John Grotzinger has been heavily involved in planning community workshops for selecting the landing site for MSL. The 4th workshop just took place September 27-29, 2010 in Monrovia, CA. A series of videos has also been produced about MSL:

Mars Science Laboratory Overview can be found here:
(http://marsprogram.jpl.nasa.gov/msl/multimedia/videos/movies/MSL_overview_Cap.mov)

MSL’s first drive in the clean room of JPL can be found here:
http://marsprogram.jpl.nasa.gov/msl/multimedia/videos/movies/msl_20100723_bldgcuriosity-640.mov

By studying MSL and its astrobiological implications and presenting it to not just young children, but the community, we are promoting science education and getting the community excited about future Mars exploration missions. As a team, we are committed to sharing the exciting science that we do with others.