What did early life use to metabolize if not oxygen respiration? In this video, I talk about all the compounds that nonoxygen loving life uses for their metabolism and how early life was affected by the build up of molecular oxygen (O2) on Earth. Alone, oxygen was toxic to most (if not all) life at the time, but oxygen also reacted with other chemicals to form more materials for this life to use in their metabolism (so it had both bad and good effects on life). This shift in the compounds available for life caused shifts in the C, S, and N cycles, in some cases even leading to the evolution of new types of metabolisms/organisms. Eventually, organisms evolved to use oxygen itself, which led to larger, more complex organisms due to the higher energy yield allowed by oxygen respiration (as long as they had the necessary enzymes to protect themselves from the harmful oxidant byproducts: antioxidants). This expanded the metabolic redox cycle maintained by oxidizing organisms and reducing organisms. But because oxygen releasing organisms (photosynthesizing cyanobacteria) dominated so greatly, they shifted the balance of this cycle toward more oxygen production that couldn't be balanced by reducing organisms, which led to the great oxidation event (GOE). The consequence of the GOE was one of the greatest mass extinctions of all time due to the toxicity of oxygen to organisms living at this time. But another mass extinction was caused at the time by the over consumption of nutrients (such as phosphorous) leading to extinctions among primary producers (photosynthesizing oxygen producers, cyanobacteria). In other words NOBODY was safe! Every type of organism underwent extinctions during this time. Thankfully, life recovered and rebalanced the cycles, and eventually (over a billion years later) oxygen allowed large eukaryotic animals to evolve (which eventually led to us!).

References: Geomicrobiology: https://amzn.to/2WAloTR
Earth System History: https://amzn.to/3v1Iy0G

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!)

Studying for an exam? Schedule Tutoring with me: https://GEOGIRLTutoring.as.me/

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Nontextbook 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
Carbonneutral pencil bag: https://shrsl.com/3cvjv
Carbonneutral backpack: https://shrsl.com/3cvkc

0:00 First Organisms on Earth
1:50 Change in S & C cycles
4:18 Change in N cycle
6:57 Higher Energy Yield of O2 Respiration
8:54 New Aerobic Metabolisms
9:46 Metabolic Redox Cycle
11:55 Imbalanced Cycle Caused GOE
13:52 Oxygen Caused Mass Extinction
16:13 A 2nd Mass Extinction (Feast to Famine)
19:03 Ozone Layer Protected Land Life
19:51 Sulfide Producers Kept Oceans Anoxic
22:32 Oxygen Allowed Eukaryote Evolution
23:52 Related videos & references

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