TLDR: I performed a biomarker analysis on rock samples from the Cryogenian to understand the rise of complex life forms to ecological significance. Rock composition and thermal maturation of samples was considered, while care was taken to prevent contamination of the biomarker signals. A summery of my research was published in the peer-reviewed MIT Undergraduate Research Journal (MURJ), hosted at the bottom of the page.
Biomarker Analysis from Svalbard in the Neoproterozoic through Micro-abrasion
Analysis of Samples from the Polarisbreen
Understanding the rise of complex life is instrumental to understanding the evolutionary history of life on Earth. The complexification of life is hallmarked by a variety of factors including the evolution of cell differentiation, multicellularity, and the development of organelle within cells. It is widely accepted that the first complex life originated at least 1 Ga, with the earliest estimates predicting its rise as early as 1.85 Ga (Knoll et. al., 2006), yet its proliferation isn’t recorded in the geologic record until the late Neoproterozoic, just after the Sturtian and Marinoan snowball Earth events (Kirschvink, 1992). Evidence can be found in sterane groups preserved in the geologic record that serve as biomarkers (Grantham and Wakefield, 1988), allowing insight to the types, metabolisms, and relative abundances of life over the time period recorded in the sediment. Identifying endogenous steranes and other biomarkers in the geologic record allows for identification of the relative abundances of bacterial vs. eukaryotic contributions to primary productivity as well as a greater understanding of the dominant metabolic pathways of the time. This research looks to understand the change in abundances of various biomarkers to better understand the expansion of eukaryotic primary productivity through the proliferation of algae in this time period
Plan of Work
My research into rocks from Svalbard look to elucidate biomarker signals from the Cryogenian between the Marinoan and Sturtian glaciation events. By performing a total lipid extract on micro-abraded samples, I hope to show evidence of the proliferation of eukaryotic primary productivity during this time period.
Step 1: Preprocessing Samples
Samples for biomarker extraction were collected from the Neoproterozoic strata of NE Svalbard by Drs. Kristin Bergmann and Tyler Mackey. Samples for this study are selected targeting sites bracketing the Neoproterozoic Snowball Earth events from areas with the lowest level of thermal alteration. Then the outer layer of each sample must be chiseled off to remove potential contaminants with solvent cleaned tools.
Step 2: Micro-abrasion Setup
Once the sample’s exterior is removed, the sample is split into cubes roughly 2 cm3. These cubes are then massed and added to a custom stainless-steel hopper with ceramic pieces, carbide, and water. The micro-abrasion setup (Jarrett et. al., 2013) is then left running until roughly ¼ of the mass of the rock has been abraded. The hopper is then filled with water and the abrasion set up is turned on for 10 seconds to loosen the slurry. The water is then pipetted off with solvent cleaned pipettes. This process is repeated 2-3 times, or until the slurry has been successfully removed. The slurry is transported to solvent cleaned Teflon tubes. These tubes are then centrifuged, and the water is poured off. The remaining sample is freeze-dried overnight, and then powdered. The process is then repeated on the samples previously set aside, and the final pieces of the sample are run through the shatterbox and powdered. The shatterbox uses a stainless-steel puck and bowl to powder small rock samples. Each stage of the process produces a powder which is dried, massed, and set aside. At the end of each abrasion the ceramic pieces are also massed to determine how much, if any, of the ceramics were abraded and ended up in the slurry.
Step 3: Preparation for Accelerated Solvent Extraction (ASE)
Before the ASE can occur, the compacted powder must be ground up using a pestle. To prepare the sample for extraction, it must be prepared in an ASE cell. To prepare the cell, one must first layer filter paper and 2-3 cm of sand, with the filter paper bookending the sand. Then the sample can be added to the cell, with glass beads dispersed throughout to ensure an even distribution of solvent during the extraction. The sample is capped with filter paper and an additional layer of sand, and aic-22 standard is added to measure precision during the analysis of the Total Lipid Extract (TLE). All unused sample is massed to determine how much sample each cell contains.
Step 4: Accelerated Solvent Extraction
After each sample is prepared in an ASE cell, the cells are inserted in the ASE machine. The machine runs 9:1 DCM:Methanol through the cells at high temperature and pressure, capturing organic molecules suspended in the powder. The machine collects the aggregate solvent and organic molecules in a small vile. This is the output that is used for analysis. The remainder of the sample can be saved for possible future analysis.
Step 5: Analysis via Gas Chromatograph-Mass Spectrometry
Once the TLE is complete, the sample should be concentrated using the turbo vap until near dryness. The remaining sample is then removed from the turbo vap in order to prevent volatile organic molecules from being lost. The sample is allowed to come to complete dryness on its own. Pentane is then added and put in the freezer overnight, allowing for asphaltene precipitation. The solution is then pipetted off and allowed to dry almost completely. Hexane is then added and the solution is combined with HCl-activated copper beads. Sulfur reacts with the copper beads to produce copper sulfide, turning the beads black. The solution is mixed with activated copper beads until the beads no longer turn black when shaken, at which point the solution can be considered desulfurized. Half the solution is saved as a record, and the remainder is injected into the QQQ with D4, n-Dodecane-d26, n-Hexadecane-d34, D2 C27 Cholestane, Naphthalene-d8, Phenanthrene-d10, Dibenzothiphene-d8, and d2 C28 Triaromatic Steranes. These standards measure the precision of the QQQ analysis. The analysis will look to identify various biomarkers already noted including various steranes and hopanes using the Mass Hunter software.
Over the course of the term, we aim to analyze 10 samples relevant to the goals of the study. They cover the Neoproterozoic Polarisbreen Formation, found in the Buldrevagen and Dracoisen regions of Svalbard. By the end of the term, all 10 samples, representing 30 extractions, should be processed. Previous samples still need to go through the shatterbox, and then a total lipid extract will be performed on each. The results of the study will be compiled and presented to the Summons research group, and a paper will be written drawing conclusions. To our knowledge, no literature thus far has produced a biomarker study spanning this transitional time period from a continuous sedimentary record. Svalbard is unique in that it provides continuous deposition across the late Neoproterozoic and is well-constrained stratigraphically, allowing for potentially the most comprehensive analysis of this time period to date. Doing so will yield valuable data that can be used to draw conclusions about the ecosystems during this time.
Published summary of my research: (p. 27-28)