Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references. / Radioisotopic dating can provide critical constraints for understanding the rates of tectonic, dynamic and biologic processes operating on our planet. Improving the interpretation and implementation of geochronologic data by coupling it with numerical modeling studies is the central theme of this thesis. Each chapter works to address a variety of problems in the Earth sciences. In each study, the interpretation of geochronologic data is aided with a numerical model that simulates the long-term behavior and/or initial conditions of the U-Pb system and provides an effective means of exploring the parameters that influence a calculated date. The record provided by geochronologic data is then coupled with models to quantitatively determine rates of geologic process on Earth. This approach permits geochronologic data to move beyond just establishing a relative time line of events. Using this dual modeling approach, Chapters 2-5 work to measure the long-term cooling and erosion rate of the lithosphere, specifically constraining the time scales and rate of transition between the stages of mountain belt formation and stability. Chapter six works to constrain the timing and duration of Central Atlantic Magmatic Province flood basalt volcanism and its relationship to the end Triassic mass extinction. The seventh and final chapter uses high precision U-Pb geochronology to evaluate the reliability of an Ar-Ar standard often used as a fluence monitor. The overall focus of this thesis has been to push the envelope of geochronologic precision and accuracy while coupling the data with modeling studies to yield new insight into Earth systems. / by Terrence Blackburn. / Ph.D.

Thesis (Ph. D. in Physical Biology)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 201-224). / The relationship between structure and function is a longstanding and central topic in biology, evolution, and ecology. The importance of morphology is clearly visible in the diverse forms taken by innumerable organisms in order to perform a myriad of functions. Examining the great variety of morphological characteristics it would seem that the overall principle of evolution is the only way to generalize the observed diversity: given differences in environments and random biological variation a great multitude of body plans have been invented as adaptations to many dynamic habitats given specific evolutionary histories. In this thesis I will show how focusing on diverse organisms makes it possible to identify common first-order laws of evolutionary organization. More specifically I will show how these common laws derive from a connection between organism structure, physical limitations, environmental constraints, and basic metabolic, biochemical, or energetic principles. Furthermore, I will show how this top level of biological organization holds significant predictive power for regional ecology and for interpreting the general trends of evolutionary history. In Chapter 2 we begin by deriving a model for the growth of single cells and populations of cells. This model is based on the partitioning of metabolic resources and the scaling relationship between metabolism and body size. We show that the growth of diverse classes of organisms is connected by common unit energetics. However there exist striking differences in the broad trends between growth rate and body size across these different classes and we show that this is a consequence of major evolutionary transitions which adjust the partitioning of metabolic resources. We interpret major evolutionary transitions to occur in response to energetic limitations. We also find that multicellular living for unicellular organisms provides a metabolic and reproductive advantage. In Chapters 3 and 4 we further investigate these features in microbial biofilms which exhibit rich spatial patterning. Using a mathematical model and experimentation we find that the tall vertical structures produced by these biofilms have optimal geometry for resource uptake and the growth efficiency of the entire colony. Our model allows us to predict the observed changes in feature geometry given alterations to the environmental conditions that the biofilms are grown in. Furthermore, we are able to show that the morphology of these structures is dependent on single cell physiology. For example, single genetic knockouts of flagellar motility radically alter the temporal dynamics of feature spacing. Our work highlights morphology as a central property in multicellular organisms which mediates the interaction between environmental conditions and physiology. In Chapter 5 we highlight the importance of morphology in complex multicellular life where we develop a general model of tree architecture which we link to physiological success within a given environment. Although this model is general, uses only tree size as a governing parameter, and does not consider speciation we are able use local resource availability to predict broad regional patterns in plant traits such as maximum tree height. Each of these chapters highlights the importance of structure and morphology at multiple biological scales. In Chapter 6 we show how the importance of structure extends to the genetic level where the specific encoding of a gene can have implicit information and functionality beyond the basic translation of codons. We investigate the observed implicit function of dramatic and frequent changes in the mutation rate of an organism given the structure of the mutL gene. We show mathematically that altering mutation rates is an evolutionarily advantageous strategy, and we show bioinformatically that the specific genetic structure that gives rise to this trait is under positive evolutionary selection. / by Christopher Andrew Poling Kempes. / Ph.D.in Physical Biology

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1988. / Includes bibliographical references. / by Michael Baldwin Baker. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 85-88). / The photometric precision needed to measure a transit of small planets cannot be achieved by taking observations from the ground, so observations must be made from space. Mid-sized nanosatellites can provide a low-cost option for building an optical system to take these observations. The potential of using nanosatellites of varying sizes to perform transit measurements was evaluated using a theoretical noise budget, simulated exoplanet-transit data, and case studies to determine the expected results of a radial velocity followup mission and transit survey mission. Optical systems on larger mid-sized nanosatellites (such as ESPA satellites) have greater potential than smaller mid-sized nanosatellites (such as CubeSats) to detect smaller planets, detect planets around dimmer stars, and discover more transits in RV followup missions. / by Rachel Bowens-Rubin. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 88-93). / The atmospheric component of the global biogeochemical mercury cycle was studied to determine the mechanisms behind diurnal trends and amplitudes in elemental and reactive gaseous mercury concentrations over terrestrial environments. This analysis was done using the 3D GEOS-Chem chemical transport model and the creation of a simple one-box model. Mercury is a significant neurotoxin for humans and other species that has been addressed in the policy realm on both national and international levels. Being able to model atmospheric mercury processes correctly is an important part of regulation and policy drafting. GEOS-Chem model results were compared with Weiss-Penzias et al. [2009] measurements for three Nevada, USA sites. The magnitude of elemental mercury concentrations differed by 0.07-0.2 ng/m3 , with GEOS-Chem underestimating concentrations due to an under-representation of mercury emissions at naturally enriched sites. The amplitude of reactive gaseous mercury diurnal variations differed by a factor of 3-4, with GEOS-Chem underestimating the diurnal trend. Based on the diurnal nature of this error, it is hypothesized that GEOS-Chem under represents the magnitude of elemental mercury emissions, the amount of oxidation occurring in the atmosphere, and the scale of entrainment from the free troposphere. / by Anastasia F. Maheras. / S.B.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Bibliography: leaves 108-113. / by Rui Vasques de Melo Ponte. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 55-57). / Dating back to 3.5 Gya, stromatolites, which are composed of laminated and lithified carbonate rock, may contain the earliest records of phototaxis, photosynthesis, and oxygenation of the environment. The reconstruction of the co-evolution of biology and the environment using stromatolites depends on the ability to recognize macroscopic shapes that arise uniquely as a consequence of microbial processes. Our investigation aims to understand the biological factors in the formation of conical structures and stromatolites. To elucidate the role of the cyanobacteria, we enrich cyanobacteria from modern hot-spring communities of cone-forming microbes and subsequently test how the formation of conical structures depends on individual strains of the community. In our analysis, we augment morphological identification by genomic analyses of the 16S ribosomal DNA. Through a combination of mixing isolated heterotrophic bacteria and enriched filamentous cyanobacteria communities, we find that heterotrophic bacteria are a determinative factor in the formation and morphology of conical structures. Further, our experiments show the mere presence of a thin, filamentous cone-forming cyanobacteria phenotype is not a sufficient condition for cone formation. / by Alexander Joseph Evans. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. / Page 231 blank. / Includes bibliographical references (p. 221-230). / In this thesis, we investigate atmospheric water vapor transport through a distinct synoptic phenomenon, namely, the Tropospheric River (TR), which is a local filamentary structure on a daily map of vertically integrated moisture flux. Firstly, an automated procedure for identifying and tracking these rivers (named TRICKS, i.e., the Tropospheric River Identifying and traCKing Scheme) is described and its performance is evaluated. This procedure enables the maxima of moisture flux (so-called TR cores) to be detected and accurately located. The relationships among the adjacent TR cores are then evaluated to construct the axes of rivers. A river is tracked from birth to termination and its life cycle properties are recorded, thus allowing various statistics of TR distributions and movements to be estimated. All these stages of the scheme are performed without intervention once a number of governing constants have been decided upon. We then apply the scheme to the vertically integrated moisture flux calculated from 43 years of 6-hourly NCEP/NCAR reanalyses and present a climatology of mean TR behavior. On average, there are 4 - 5 rivers per analysis in the Northern Hemisphere and 5 in the Southern Hemisphere. Northern Hemisphere TRs form and intensify near the eastern seaboards of Asia and North America. They move eastward and poleward during their lives before weakening in the two principal graveyards: over the Gulf of Alaska and the region to the southeast of Greenland. In comparison, Southern Hemisphere TRs are more evenly distributed and tend to form in a band extending from the southeast coast of South America into the Atlantic, across the Indian Ocean, and throughout much of middle latitudes of the Pacific sector. / (cont.) The corresponding genesis regions are also found to be adjacent to (or slightly equatorward to) the maximum SST gradients in these regions. It appears that both TR genesis and termination maxima tend to be displaced near the upstream equatorward flanks of cyclogenesis and lysis maxima. We suggest that the TR formation and termination could be a leading predictor for the occurrence and decaying of extratropical cyclones. TR axis length appears to be longer during the warmer season and in the Southern Hemisphere. The distance traveled by TR systems shows a broad distribution and a sizeable fraction (-25%) of systems travel in excess of 3000 km. One unique feature is that although TRs occur very actively over the Indian ocean sector with highly densed tracks, large translational speeds, and intensities, they contribute little to meridional water vapor transport, while the reverse situation can be found in the South Pacific where southward transport is sometimes comparable to those over or off the east coast of South America. The rivers seem to account for a substantial fraction of the total meridional moisture transport in both middle and subtropical regions. Finally, we complete the TR climatology with an analysis of the variability and trends exhibited by many aspects of rivers during the 43-year period. The annual average number of TRs per analysis has undergone an overall increase during the last couple of decades and is more significant in the Southern Hemisphere. The greatest increases occur in the 50⁰-30⁰S and 50⁰-70⁰N belts ... / by Yuanlong Hu. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2009. / Cataloged from PDF version of thesis. Original thesis missing page 55. / Includes bibliographical references (pages 71-72). / Air traffic managers need up to date nowcast information over the entire CONUS for efficient operations in the National Airspace System. In areas of degraded or no radar coverage, cloud-to-ground lightning (provided by the National Lightning Detection Network) can provide valuable information through the creation of proxy vertically integrated liquid (VIL) and echo tops (ET). To develop these lightning-VIL and lightning-ET relationships, analysis of the lightning and radar data was done in "climate zones" throughout the CONUS, due to the potential for different lightning behavior in different areas of the country. After a quantile analysis revealed differences in the data between zones, lightning-VIL. and lightning-ET relationships were developed using a probability matching method for a baseline relationship (all climate zones) and for each individual climate zone. The potential benefits of the inclusion of each zone were analyzed through a bootstrap testing of the proxy VIL and proxy ET models, and performance was assessed using a system of binary scoring. For a given lightning flash rate, VIL values in the Mid-Latitude Land West zone were considerably lower than in other zones. The Mid-Latitude Land West zone also showed a noticeable improvement in the performance of the proxy VIL model. For a given lightning flash rate, ET values in the Mid-Latitude Water zone were considerably lower than in other zones. The Mid-Latitude Water zone appeared to provide a statistical improvement in the proxy ET model, but because of a lack of data in this zone on the days chosen for model testing, this improvement was not noticeable in the overall performance of the proxy ET model and needs to be investigated further. / by Erin B. Munsell. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 235-251). / This dissertation presents data processing techniques relevant to the acquisition, modeling, and inversion of self-potential data. The primary goal is to facilitate the interpretation of self-potentials in terms of the underlying mechanisms that generate the measured signal. The central component of this work describes a methodology for inverting self-potential data to recover the three-dimensional distribution of causative sources in the earth. This approach is general in that it is not specific to a particular forcing mechanism, and is therefore applicable to a wide variety of problems. Self-potential source inversion is formulated as a linear problem by seeking the distribution of source amplitudes within a discretized model that satisfies the measured data. One complicating factor is that the potentials are a function of the earth resistivity structure and the unknown sources. The influence of imperfect resistivity information in the inverse problem is derived, and illustrated through several synthetic examples. Source inversion is an ill-posed and non-unique problem, which is addressed by incorporating model regularization into the inverse problem. A non-traditional regularization method, termed "minimum support," is utilized to recover a spatially compact source model rather than one that satisfies more commonly used smoothness constraints. Spatial compactness is often an appropriate form of prior information for the inverse source problem. Minimum support regularization makes the inverse problem non-linear, and therefore requires an iterative solution technique similar to iteratively re-weighted least squares (IRLS) methods. / (cont.) Synthetic and field data examples are studied to illustrate the efficacy of this method and the influence of noise, with applications to hydrogeologic and electrochemical self-potential source mechanisms. Finally, a novel technique for pre-processing self-potential data collected with arbitrarily complicated survey geometries is presented. This approach overcomes the inability of traditional processing methods to produce a unique map of the potential field when multiple lines of data form interconnected loops. The data are processed simultaneously to minimize mis-ties on a survey-wide basis using either an 12 or 11 measure of misfit, and simplifies to traditional methods in the absence of survey complexity. The 11 measure requires IRLS solution methods, but is more reliable in the presence of data outliers. / by Burke J. Minsley. / Ph.D.