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Foundations of Complex Life: Evolution, Preservation and Detection on Earth and Beyond

If we cannot detect complex life on Earth when it first arose, how can we hope to detect life on other planets? A major theme of the MIT team’s research is taphonomy. Taphonomy is the combination of processes and conditions that preserve biological signatures. Throughout their work they address issues of taphonomy during the late Mesoproterozoic and Neoproterozoic as an analog for planetary exploration. This time interval preserves a sparse but tantalizing record of increasingly complex life as viewed through fossils, isotopes, and organic molecules but it is not as adversely affected by tectonic disturbance as older records.

The research of the MIT team is organized under five themes:

Theme I: The Earliest History of Animals: The Search for the Missing Evidence.

The MIT research team pursues a series of linked projects to further explore the causes of the early divergence of animals and the factors underlying their long missing history during the Cryogenian and Ediacaran. In addition, they seek to understand the principles and mechanisms that determine the preservation of organic matter and fossils, through time and in relation to the progressive evolution of ocean-atmosphere chemistry. Environments of exceptional preservation are also being explored, as are the roles of specific minerals (such as clays) in the selective preservation of organic molecules. The results of this research informs our understanding of the potential for biosignature preservation elsewhere in the Solar System, including in Gale Crater.

Theme II: Paleontological, Sedimentological and Geochemical Investigations of the Mesoproterozoic Era through Cryogenian Period.

In contrast to the canonical view, emerging research on Neoproterozoic sedimentary successions by the NAI MIT team indicates that much of the apparently sudden rise of animal life in the Ediacaran sedimentary record was initiated earlier, during the late Mesoproterozoic Era and through the Cryogenian Period (1200 – 650 Ma). Consequently, this team seeks to document the stratigraphy, isotopic records, macroscopic and microscopic fossil assemblages and biomarker contents of well-preserved Mesoproterozoic and Neoproterozoic sections from Northwestern Canada and Russia. These records will make it possible to track the origin of complex protists and animals from the biologically simple eukaryotic world of the Mesoproterozoic. To complement their geological and paleontological work, they will also initiate a series of taphonomic experiments to explore the preservation pathways of protist groups through time. This will give a clearer picture of both the ‘true’ diversity of eukaryotes during the Proterozoic and provide information on fossil preservation that can be extended to other sites of astrobiological interest.

Theme III: Neoproterozoic Aerobic Transition: A Preservation-induced Tipping Point.

The appearance of complex life roughly coincided with the Neoproterozoic oxygenation of the oceans, however the causes of this major environmental transition are poorly understood. Current understanding suggests the increased oxygen concentration was driven by the preservation of organic carbon, therefore, the MIT team is investigating the stability of the biosphere-geosphere system as a function of changing organic preservation during the Neoproterozoic. Specifically, they hypothesize a positive feedback through microbial priming, where increasing oxygen concentrations in surface oceans accelerated the removal of labile organic material, but increased the preservation of recalcitrant organic matter and overall organic burial.

Theme IV: Taphonomy, Curiosity and Missions to Mars.

The scientific mission of the Mars Science Laboratory rover, Curiosity, is to characterize an environment on Mars that may have once been habitable. The knowledge that Mars may have experienced a warm and wet early period led to the concept of taphonomy (i.e. preservation and fossilization processes) being a major driver in the selection of Gale Crater as a landing site for Curiosity. To maximize our understanding of preservation on Mars, the MIT is pursuing a multi-pronged approach to integrating research on Mars and Earth to understand Martian environments and geochemistry. The team is focusing on: 1) evaluating depositional environments and the history of diagenesis within Gale Crater; 2) characterizing minerals and their transformations during diagenesis both in Gale Crater and in terrestrial analogs; and 3) evaluating possible Mars-relevant taphonomic windows in terrestrial analogs.

Theme V: Synthetic Activities.

The history of Earth is marked by a series of major transitions, some physical, others geochemical, and some biotic. There is, therefore, a critical need for synthetic activities to generate an expanded view of major evolutionary transitions. In the same vein, the environmental history of Mars is currently viewed in terms of crude evaluations of past climate, the availability of standing water, surface redox conditions and atmospheric composition. However, improved knowledge and understanding will emerge from the MSL mission over the next 3-4 years. This creates an ideal opportunity for the MIT team to engage with others within NAI and the MSL science community to develop a synthesis of the history of biological habitability on Mars.