Part 5

Part 5: The Origin & History of Life

Overview

• Topics covered in this section:

  • The origin of the solar system

  • The beginning of life

  • The earliest life forms

  • Evolution into multicellular life

  • Life transitioning onto land

  • General timelines of animal and human evolution

Page 1: The Origin of the Solar System

• A PBS NOVA video titled "Where Did We Come From?" is recommended for streaming.

• Additional resources for viewing:

  • YouTube link

  • Amazon rental option for $2.99

Page 2: Early Earth Conditions

• Early Earth had a substantially different atmosphere:

  • Lack of oxygen and ozone

  • High UV radiation exposure

  • Rich in methane, ammonia, water, and hydrogen

  • Frequent meteorite impacts and volcanic eruptions

  • Presence of electrical storms and lightning

Page 3: Prebiotic Simulations

• 1950s experiments simulating early Earth conditions (prebiotic simulation):

  • Mixed gases present in early Earth and added energy sources (electricity, UV light, or heat)

  • Resulted in the formation of organic molecules within days.

  • Organic molecules = building blocks of life.

Page 4: Leading Hypothesis for Life's Origin

• Continued experiments support the hypothesis that:

  • Simple organic molecules combined to create complex structures leading to the earliest cells.

• This process took nearly a billion years for the initial life forms to emerge.

Page 5: Pathway to Cellular Life

Stages in the origin of cells

1. Simple precursor chemicals in a watery environment ("soup")

   • CO₂, H₂, H₂O, NH₃ present

2. Formation of small organic molecules

   • Chemical reactions produce amino acids and lipids.

3. Joining of monomers into polymers

   • Formation of polypeptides and nucleic acids.

4. Genetic material encodes proteins

   • Lipids create membrane-bound structures.

5. Formation of protocells

   • Self-replicating systems encapsulated in membranes.

Page 6: Alternative Theories for Life's Origin

• The idea of "Panspermia":

  • Suggests life may have originated from extraterrestrial conditions, supported by findings of organic molecules in meteorites.

Page 7: Conditions for Life Formation Today

• Current conditions on Earth differ significantly from early Earth:

  • Reduced volcanic activity and electrical storms

  • Presence of predatory microbes would hinder the formation of new organic compounds.

Page 8: The Earliest Life Forms

• Earth formed ~4.5 billion years ago.

• Life developed over almost a billion years, with oldest fossils (~3.5 billion years) being prokaryotes (primitive bacteria).

Page 9: Prokaryotic Growth and Photosynthesis

• The first prokaryotes thrived in ocean environments, competing for organic molecules.

• After a few hundred million years, photosynthetic prokaryotes emerged:

  • Utilized sunlight for energy, creating an ecological advantage.

Page 10: Impact of Photosynthesis on Earth's Atmosphere

• Photosynthesis produced oxygen (O₂), essential for the development of Earth’s atmosphere.

• Significant oxygen levels appeared ~2 billion years ago, leading to major evolutionary shifts.

Page 11: Emergence of Aerobic Metabolism

• The rise in O₂ levels allowed the evolution of aerobic metabolism:

  • Aerobic organisms harvest significantly more energy compared to anaerobic (prokaryotic) organisms.

• Increased energy levels led to competition, enhancing natural selection and contributing to the evolution of complex eukaryotic cells.

Page 12: Diversification of Life

• The increase of O₂ and protection from UV rays led to greater biodiversity.

• The last common ancestor of all current living organisms appeared ~3 billion years ago.

Page 13: Multicellular Evolution

• Evolution towards larger cells provided advantages:

  • Larger cells could capture and consume smaller cells.

  • However, there were disadvantages regarding diffusion of gases and nutrients.

• Solution: evolution of multicellular organisms allowing for specialization of cells.

Page 14: The First Multicellular Organisms

• Multicellular life emerged ~1.2 billion years ago, starting with algae in oceanic environments.

• Specialization of cells provided various ecological advantages.

Page 15: Transition to Life on Land

• Life began to transition onto land approximately 475 million years ago with the first plants.

• Animals followed roughly 400 million years ago.

Page 16: Challenges for Terrestrial Life

• Land organisms faced several challenges:

  • Need to support own weight versus buoyancy in water.

  • Searching for water sources.

  • Protecting reproductive gametes from dehydration.

Page 17: Advantages of Land Life

• Plant life slowly expanded from shallow waters to shores, gaining advantages:

  • Photosynthesis more efficient outside water.

  • Access to nutrient-rich soil versus nutrient-limited seawater.

  • Initial absence of land-based predators.

Page 18: Adaptation of Early Terrestrial Animals

• Early lobefin fishes adapted to terrestrial life, enabling movement across land during dry conditions.

Page 19: Evolution of Amphibians and Reptiles

• Lobefins evolved into amphibians, requiring proximity to water for reproduction and hydration.

• Some amphibians adapted to drier environments, leading to the evolution of reptiles, which developed:

  • Waterproof reproductive eggs.

  • Scaly skins to retain moisture.

  • Improved lung functionality.

Page 20: Dominance of Reptiles

• As climate shifted, reptiles became dominant on land, leading to the rise of diverse dinosaur groups.

• Dinosaurs thrived for over 150 million years alongside numerous smaller reptiles and amphibians.

Page 21: Insulation Evolution in Reptiles

• Evolutionary adaptations to retain heat:

  • Feathers in some reptiles led to the emergence of birds.

  • Hair in others led to early mammals.

Page 22: Human Ancestors

• The earliest primates appeared 55 million years ago, exhibiting key traits:

  • Opposable thumbs, flat nails, and enhanced binocular vision.

Page 23: Evolution of Hominins

• Hominins (humans and their extinct relatives) emerged approximately 6 million years ago, with a complex evolutionary history.

Page 24: Australopithecines

• The genus Australopithecus arose about 4 million years ago, containing several extinct species recorded in the fossil record.

Page 25: Evolution of the Homo Genus

• Genus Homo branched from australopithecines ~2.5 million years ago, with noticeable increases in body and brain size.

• Further species discoveries are ongoing within the Homo lineage.

Page 26: Migration Patterns of Early Humans

• Homo erectus, first hominin to leave Africa, ventured into Asia but went extinct for unknown reasons.

Page 27: Neanderthals and Modern Humans

• Neanderthals inhabited Europe ~300-400 thousand years ago and became extinct ~30 thousand years ago.

• Genetic analysis shows a close relation between Neanderthals and modern humans.

Page 28: Modern Human Development

• Homo sapiens originated in Africa ~150,000 years ago, with genetic and fossil analysis tracing modern human migration around the globe.

Page 29: The Earliest Modern Humans Outside Africa

• The oldest known modern human fossils outside Africa date back 90,000-120,000 years.

Page 30: Evolutionary Perspective

• Dinosaurs thrived for ~164 million years before extinction; modern humans have existed for only a few million years.

Page 31: Genomic Insights on Human Migration

• Research indicated that populations outside of Africa exhibit less genetic diversity compared to African populations, supporting the founder effect hypothesis.

Page 32: Conclusion on Human Evolution

• Globally, humans share ~99.9% genetic similarity, highlighting our common ancestry despite diverse appearances.

Page 33: Further Study Resources

• Additional viewing resources on the subject are provided, particularly the PBS NOVA videos.