History of earth- bio 61

• Life started on this planet and evolved into the current diversity
• Life doesn't just spontaneously occur, as shown by experiments like those of Louis Pasteur
• Louis Pasteur's experiments


  He made bottles with an S-curve that prevented air particles from entering the broth, which remained sterile over time. When he broke the bottle or tilted it, growth would occur, showing that microbes from the air cause food to go bad, not spontaneous generation
• Spontaneous generation was contradictory to the fact that life had to start somewhere
• Oparin and Haldane's hypothesis

  They proposed that the early Earth's atmosphere, with abundant water, hydrogen, nitrogen and methane, could create biomolecules and lead to the start of life
• Early Earth's atmosphere


  • No oxygen, water mostly in the atmosphere rather than oceans, faster rotation, shorter year
• Miller-Urey experiment


  Boiling chamber to simulate early Earth conditions, produced basic organic compounds like amino acids and nucleotides
• Miller-Urey saw both left-handed and right-handed molecules form, not just the common ones
• One life form may have evolved to be more efficient and outcompete others in the early Earth
• Role of clays


  Inorganic clays with positive charge attracted negatively charged biomolecules, providing a substrate for them to interact and form more complex molecules
• Protocell


  A simple phospholipid bubble containing self-replicating RNA that could catalyze reactions, but lacking some features of modern cells like a nuclear membrane and DNA
• RNA was likely the first self-replicating molecule, before the development of DNA
• Earth formed around 4.5 billion years ago from an accretion disk, was initially very hot and volcanically active
• The Moon's tidal effects prolonged Earth's volcanic activity, creating a prebiotic soup
• First evidence of life on Earth, prokaryotic cells resembling archaea


  3.9-4 billion years ago
• Early life was anaerobic, living in extreme conditions like deep ocean vents, protected from intense UV radiation
• Photosynthesis originated around 3.5 billion years ago, leading to accumulation of oxygen in the atmosphere over 1.3 billion years
• Oxygen first accumulated in the atmosphere before the deep oceans due to its low solubility in water
• Even with our rich oxygen atmosphere, beyond a meter into the ocean the water becomes increasingly oxygen deprived
• Aerobic zone


  The surface where photosynthetic cyanobacteria are and their predators
• Anaerobic zone


  The deep ocean
• Predators dealt with the accumulation of oxygen by binding it to iron, creating a rust layer in the earth
• Eukaryotes


  Cells with a membrane-bound nucleus and organelles, formed around 1.3 billion years ago as volcanic activity slowed down
• Formation of eukaryotes


  1. Archaea cell becomes larger and takes in part of its membrane to form small vesicles internally

  2. Migrates from volcanic vents towards the surface

  3. Engulfs an anaerobic bacteria
• Eukaryotic cells have mitochondria, which came from the engulfed anaerobic bacteria
• The engulfing of the mitochondria is the synapomorphy (shared derived characteristic) that defines eukaryotic life
• Some eukaryotic cells later engulfed photosynthetic cyanobacteria, giving rise to chloroplasts and modern plants
• This engulfment of chloroplasts has happened multiple times, giving rise to different algal lineages
• Evidence for endosymbiosis includes DNA, ribosome, and other structural similarities between mitochondria/chloroplasts and their bacterial ancestors
• Multicellular life appeared quickly, about 100 million years after eukaryotes, as larger cells could better avoid predation
• Photosynthetic organisms formed colonies and division of labour to overcome this surface-to-volume issue
• The Paleozoic era saw a rapid diversification of marine life, the invasion of land by plants and animals, and three mass extinction events
• The Cambrian explosion saw the first major diversification of marine life, including the first vertebrates and arthropods
• In the Ordovician, marine life was dominated by arthropods and mollusks, and plants first invaded land
• The Ordovician-Silurian mass extinction was likely caused by a drawdown of atmospheric CO2 leading to global cooling and glaciation
• About 430 million years ago, arthropods first invaded land, followed by the first land vertebrates about 400 million years ago
• The late Devonian mass extinction was likely caused by eutrophication and algal blooms due to the spread of land fungi
• In the Carboniferous, ferns, clubmosses, and early conifers dominated the land, along with the first amphibians and insects
• The Permian mass extinction saw a decline in amphibians and the rise of reptiles
• Amniotic egg


  Allows reproduction away from water by providing a shell, gas exchange membrane, and amniotic sac to prevent desiccation