Life

Brief timeline of life on earth:

• Abiogenesis 4 bya -> first replicators -> DNA first, then Ribosomes and Proteins
• LUCA 3.5 bya -> Last Universal Common Ancestor
• Photosynthesis 2.4 bya -> cyanobacteria -> Great Oxygenation Event aka the Oxygen Holocaust
• Respiration 2 bya -> respiring (aerobic) bacteria -> the first predators and eukaryotes
• Multicellularity 1 bya -> small, mobile (basic cellular machinery/propellers) and large, immobile (the animals among these had neurons/nerve nets)
  • Known as the Ediacaran period, marked by the emergence of:
    • Fungi - external digestion of dead biomaterial
    • Animals - internal digestion of prey in a stomach cavity
      • ~550 mya -> first bilaterians (and the first brains)
• Cambrian explosion 540-475 mya (driven by an evolutionary arms race of predation)
  • Animal world dominated by arthropods
  • Humans descended from the smaller, less dominant ancient fish, the earliest vertebrates
• Move to land 420-375 mya in the Devonian period
  • Large fish dominate the water -> arthropods and other invertebrates driven to land -> insects and spiders
  • Land plants developed leaves and seeds, spread and some grew into trees. Earth became green! -> too much CO2 consumed -> Late Devonian Extinction with oceans freezing over, eradicating over half of all life.
  • Some fish had developed lungs and moved to inland puddles -> lost gills and fins -> tetrapods with four feet -> amphibians and amniotes.
• Carboniferous and Permian eras 350-250 mya -> amniotes expanded on land -> cold-blooded reptiles (immobile at night) and warm-blooded therapsids (hunted at night).
  • Therapsids came to dominate and then fell off with the Permian-Triassic mass extinction event (the deadliest one in earth's history, cause unclear) -> only the small plant-eating cynodonts survived.
• Dinosaurs 250-100 mya -> cynodonts become mammals.
• Permian-Triassic extinction 66 mya due to an asteroid -> dinosaurs go extinct, mammals take over.
  

Humans

• Apes walk upright in East Africa 4mya after geological shifts 10 mya leading to lack of tree cover.
• Oldowan tools (scavenging stone flakes) 2.5 mya.
• Homo erectus 2 mya becomes an apex predator, a hypercarnivore and endurance runner. Likely also discovers fire and cooking perhaps from the stone flake chipping process. Expanding brain size also led to premature birthing and extended care periods with high levels of father involvement (monogamy). They were the first to leave Africa.
• At least four different species of humans 100 kya -> Homo erectus, Homo floresiensis, Homo neaderthalensis and Homo sapiens.
• Homo sapiens leave Africa 70 kya and win.