Earliest Life: What Was the First Life on Earth Like? How We Study LUCA | GEO GIRL

This video is all about our guesses as to what metabolic pathway(s) the earliest life on Earth might have used! We start by going through the possibilities like photosynthesis vs chemosynthesis, then assuming a hydrothermal vent life origin, we moved on to discuss the possible chemotrophic pathways: chemoautotrophy (use inorganic carbon for metabolism) vs. chemoheterotrophy (use organic carbon for metabolism). We actually don't know for sure which one is first, but we assume a chemoautotrophic start for the rest of the discussion. We then discuss which chemolithoautotrophic pathways are most likely the earliest to evolve (both elemental sulfur reduction and sulfate reduction are possible, with the combination of Fe(III) reduction in some cases, and methane production by methanogenesis is the other main possible pathway). We further discuss the potential for these pathways to have evolved early by looking at the deepest-branching bacteria and archaea. Deep branching bacteria have the ability to reduce oxygen, nitrate, sulfur species, or iron using hydrogen (H2) as an electron donor. But we cannot pinpoint the first bacterial metabolism because lateral gene transfer (or horizontal gene transfer) prevents us from piecing together a perfect evolutionary tree. Deep branching archaea have the ability to either reduce elemental sulfur or reduce carbon dioxide to produce methane. However, sulfate reduction is present in both deep branching bacteria and some archaea, so was our last universal common ancestor (LUCA) a sulfate reducer? Again, lateral gene transfer prevents us from knowing for sure. Lastly, we discuss the first fermenting and respiring organisms. These chemoheterotrophs had to evolve to eat the organic carbon produced by the earlier chemoautotrophs. References: Geomicrobiology: https://amzn.to/2WAloTR Biology of Microorganisms: https://amzn.to/3kQqIuD GEO GIRL Website: https://www.geogirlscience.com/ (visit my website to see all my courses, shop merch, learn more about me, and donate to support the channel if you'd like!) 0:00 what this video covers 0:53 life's origins 2:26 was phototrophy or chemotrophy first? 4:07 was autotrophy or heterotrophy first? 5:08 first metabolism on Earth 6:54 how we study LUCA 7:20 deepest branching bacteria 9:32 lateral gene transfer 10:29 deepest branching archaea 12:32 was LUCA a sulfate reducing microbe? 14:04 when did fermentation evolve? 14:50 when did respiration evolve? 16:31 evolution of macroorganisms 18:00 references & upcoming videos! 19:02 my cat ;) Hey there, Earth enthusiast! Check my favorite Earth-friendly products: Bamboo toilet paper: https://shrsl.com/3cvku Bamboo paper towels: https://shrsl.com/3cvkw Compostable tableware: https://shrsl.com/3cvkz Compostable trash bags: https://shrsl.com/3cvl0 Bamboo cutlery + straw! : https://shrsl.com/3cwfl Eco-Friendly Tote (great for grocery shopping!): https://shrsl.com/3cwfp Reusable straws + cleaning brushes (my fav!): https://shrsl.com/3cwft Eco-friendly laundry detergent: https://shrsl.com/3cwgo Directly offset your carbon footprint with Wren: https://shrsl.com/3d0t2 (Just click link, press get started, take the free C footprint quiz, then choose how much you want to reduce your footprint by donating to the C sequestration projects they're funding!) Non-textbook books I recommend: Oxygen by D. Canfield: https://amzn.to/3gffbCL Brief history of Earth by A. Knoll: https://amzn.to/3w3hC1I Life on young planet by A. Knoll: https://amzn.to/2RBMpny Some assembly required by N. Shubin: https://amzn.to/3w1Ezm2 Your inner fish by N. Shubin: https://amzn.to/3cpw3Wb Oxygen by N. Lane: https://amzn.to/3z4FgwZ Alien Oceans by K. Hand: https://amzn.to/3clMx1l Life's Engines: https://amzn.to/3w1Nhke Tools I use as a geologist/teacher/student: Geology field notebook: https://amzn.to/3lb6dJf Geology rock hammer: https://amzn.to/3DZw8MA Geological compass: https://amzn.to/3hfbdLu Geological hand lens: https://amzn.to/3jXysM5 Camera: https://amzn.to/3l6fGRT Carbon-neutral pencil bag: https://shrsl.com/3cvjv Carbon-neutral backpack: https://shrsl.com/3cvkc Disclaimer: Links included in this description might be affiliate links. If you purchase a product or service with the links that I provide I may receive a small commission, but there is no additional charge to you! Thank you for supporting my channel so I can continue to provide you with free content each week! And as always, let me know your topic suggestions in the comments down below!