History of Life on Earth & Human Evolution

• Earth formed 4.5 billion years ago

• believed to be very hot, water was vapor

• lacked ozone layer, very little oxygen

• life started 3.5 billion years ago

• spontaneous generation referred by Louis Pasteur

• probable prebiotic chemical evolution (miller & vrey)

Origin of Life Hypothesis

• Clay as catalyst

• “RNA World”

• Ribozyme + Vescile = Protocell

• we don’t know for sure

Endosymbiotic Theory:

• life began with prokaryotic cells —> evolved to utilize photosynthesis or a form of cellular respiration

• First eukaryotic cells formed from symbiotic relationship of large prokaryotic cells eating smaller prokaryotic cells

• early prokaryotes that conducted respiration evolved to become mitochondria. Cells that conducted photosynthesis became chloroplasts

Evidence:

• mitochondria & chloroplasts have own DNA, organized same as bacterial DNA

• similar in size to many bacterial prokaryotic cells

• both can divide to replicate, similar to bacterial replication

Boundaries of Eras & Periods:

• Eras are marked by sharp transitions in type of abundance of life forms due to fossil evidence

• extinctions are often followed by rapid evolution of new life forms

Extinction of Earliest Organisms:

• Precambrian era (4.6 billion years to 544 million years ago) longest era

• prokaryotic anaerobes

• evolution of photosynthesis

• increase oxygen —> rise of aerobic respiration

• internal membranes of Eukaryotes

• all life exists in the sea (first multi-cellular organism = algae)

Paleozoic Era (544 MYA - 245 MYA)

• Cambrian Explosion - diverse marine invertebrates evolve (multicellular and heterotrophic)

• first fish and first fungi evolve

• primitive plants & then animals invade land

• amphibians followed by reptiles

• Pangea (one land mass)

Mesozoic Era (245 MYA - 65 MYA)

• Reptiles give rise to first mammals and birds

• dinosaurs

• gymnosperms were dominant at start; angiosperms dominant at end

• end of Era dinosaurs extinct (most marine life) continents were separated

Cenozoic Era (65 MYA - Present)

• first primates

• flourishing of birds, mammals, insects, flowering plants

• continents shifted to current locations

• evolution of Hominids gave risk to modern Homeo sapien

• All evolution does NOT lead to development of humans or an increase in complexity

Primate Evolution:

• notable trait evolution

• tree dwelling

• opposable digits

• binocular vision

• grasping hands

• large brains

• common primate ancestor gave rise to Hominids & Chimpanzees (5MYA)

Hominin Evolution

• switch to bipedalism

• gradual abandonment of tree-dwelling existence

• increasing brain volume

• tool making abilities

• all Hominin genera are extinct except Homo sapiens

Hypothesis of modern human evolution:

• all human evolution happened in Africa

• African Replacement Hypothesis - Homo Sapiens fully evolved in Africa, spread around globe replacing separate Hominin Species

• Multi-regional Hypothesis - several similar species of Hominins left Africa & Interbred in Europe and Asia, overtime evolved into Homo sapiens

Modern Homo Sapiens

• emerged 200,000 years ago

• unique characteristics took many years to evolve

  • brain size

  • ability to make tools

  • language capacity

  • stamina

  • throwing ability