Biology: How Life Works Unit 4: History of Earth & Human Society

Biology: How Life Works Unit 4: History of Earth & Human Society

Important Announcements

  • Section BB:

    • What-if calculator

  • Upcoming Assignments:

    • Survey checkpoint 2 (Individual) - Due next Monday before class.

    • Writing assignment 2 (Group) - Due Nov 21st Friday at midnight.

    • Exam 4 on Dec 3.

    • Final exam: Dec 10th @ 6 to 8 pm.

UNIT 4 Learning Objectives

  1. Compare mass extinction events throughout the history of the earth with the current rate of biodiversity loss.

  2. Identify the major threats to biodiversity caused by human activity.

  3. Describe trends in climate and atmospheric conditions over geological history.

  4. Explain how changes in environmental conditions have influenced biota, and how biological organisms have influenced Earth’s environments.

  5. Discuss how biotic and abiotic interactions influence organismal diversification and extinction.

  6. Define the Anthropocene.

  7. Describe the ecological conditions in which Homo sapiens evolved and the traits that led to their evolutionary success.

  8. Identify major population and dispersal trends in Homo sapiens over human history.

  9. Evaluate Homo sapiens as ecosystem engineers.

  10. Analyze the impacts of human activity on the carbon cycle and the feedback between the carbon cycle and global climate.

  11. Evaluate the impact of human activity on nitrogen and phosphorus cycles.

  12. Describe feedback mechanisms between biogeochemical cycles and the global climate.

  13. Relate species loss and ecosystem disruption to ecological, evolutionary, and societal consequences.

  14. Compare strategies in conservation biology to mitigate habitat degradation, loss, and biodiversity loss.

  15. Describe approaches to counteract climate change.

  16. Examine what it means for humans to live sustainably.

Earth's Historical Context & Human Existence

  • Humanity has a long and varied history.

    • Illustration: Traditionally dressed Hajong culture troupe and Russian girl in traditional costume with representatives from various cultures.

    • Reconstruction of Homo Neanderthalensis at Vienna Natural History Museum.

    • Masai of Kenya and American school children in the 1940s highlight cultural diversity.

  • Relative to Earth’s history, humans have existed for a very brief time:

    • The Earth is about 4.6 billion years old, divided into four major eons:

    • Hadean eon

    • Archean eon

    • Proterozoic eon

    • Phanerozoic eon

    • See detailed visual synthesis on page 504.

Earth's Geologic Timescale

  • 4.6 billion years ago (BYA): Earth forms.

  • 3.8–3.5 BYA: First life—anaerobic prokaryotes in oceans.

  • 2.4 BYA: Cyanobacteria release O₂ → Great Oxygenation Event; ozone layer forms.

  • 1.8 BYA: Eukaryotes arise via endosymbiosis → larger, complex cells.

Key Events in Earth's History

  • 575 million years ago (MYA): Multicellular animals diversify during the Cambrian Explosion (541-485 MYA).

  • 467–350 MYA: Life colonizes land—plants, arthropods, then vertebrates adapt to air and gravity.

  • 65 MYA: Dinosaur extinction → mammal radiation.

  • 6–7 MYA: First hominins appear in Africa.

  • ~200–300 thousand years ago: Homo sapiens evolves—large brains, tool use, culture, global spread.

iClicker Questions and Activities

  • Question: Which event occurred most recently in Earth’s history?

    • The rise and evolution of humans in the Phanerozoic Eon is the most recent event.

  • Question: Which of the following events occurred first in the evolutionary timeline?

    • Critical events include the evolution of land plants, the oxygenation of the atmosphere, etc.

Life Emergence and Evolution

  • A prokaryotic ancestor lived in early Earth’s extreme conditions:

    • Earth’s first atmosphere had little oxygen and consisted mainly of water vapor and volcanic compounds (nitrogen, CO₂, methane, ammonia).

    • Life began in oceanic environments.

Fossil Evidence

  • Stromatolites: First fossil evidence of life, dating back as early as 3.5 BYA.

    • Formed when microbial mats (including cyanobacteria) trap and bind sediment particles.

    • Indicates:

    • Life started in aquatic environments.

    • Prokaryotic life dominated early Earth.

    • Photosynthetic cyanobacteria led to the Great Oxygenation Event.

The Great Oxygenation Event

  • Cyanobacteria and O₂ Release:

    • Approximately 2.4 BYA, cyanobacteria released oxygen into the atmosphere.

    • Prior to their dominance, the Earth had virtually no oxygen.

    • The increase in oxygen likely caused mass extinctions of anaerobic bacteria and may have contributed to an ice age, paving the way for more complex organisms.

    • Cellular respiration arose as an adaptation to the new oxygen-rich environment.

iClicker Question on Stromatolites

  • Question: Relationship between stromatolites and the Great Oxygenation Event?

    • Correct Answer: B. Stromatolites mainly formed by cyanobacteria, whose photosynthesis released oxygen triggering the Great Oxygenation Event.

Impact of the Great Oxygenation Event

  • This event had huge implications for the evolution of life on Earth.

    • Led to new metabolic pathways and organism diversification.

Endosymbiotic Theory

  • Eukaryotic cells formed through endosymbiotic events:

    1. An ancestral archaeal cell engulfed an aerobic bacterium → becomes mitochondrion.

    2. Later, a heterotrophic eukaryote engulfed a photosynthetic bacterium (cyanobacterium) → evolves into plastids/chloroplasts.

  • These events allowed for increased energy efficiency and complexity, paving the way for multicellular life.

Early Animal Fossils

  • Ediacaran Period: macroscopic fossils appear around 565 million years ago.

    • For the majority of Earth’s history, only microorganisms existed.

    • Animals appeared relatively late in the evolutionary timeline with simple shapes that do not clearly match modern animals.

Cambrian Explosion

  • Period: 541-520 MYA marked by rapid diversification of aquatic life.

    • First appearances of most modern body plans, including bilaterians and early deuterostomes.

    • Key Innovations:

    • Formation of hard parts (biomineralization).

    • Development of complex eyes and sensory systems.

    • Enhanced muscular coordination and active burrowing (substrate revolution).

    • An ecological arms race with increased predation leading to adaptations for defense (spines, shells, behaviors).

Variational Factors Contributing to Cambrian Explosion

  • Question: Which combination of factors influenced the Cambrian Explosion?

    • Correct Answer: C. Rising atmospheric and oceanic oxygen, enhanced nutrient input, predator-prey dynamics, and genetic innovations.

Life on Land

  • 467 – 350 MYA: Life begins to diversify on land (fungi, plants, arthropods, then vertebrates).

    • Phylogenetic evidence suggests green algae gave rise to land plants.

    • Fungi and arthropods evolved alongside early land plants.

    • Development of land vertebrates from lobe-finned fish, with Tiktaalik as a transitional fossil demonstrating both fish and early tetrapod traits.

Mass Extinctions and Biodiversity

  • The Cambrian Explosion set the stage for the Big Five Mass Extinctions:

    • These events have drastically altered evolutionary pathways.

  • Major Mass Extinction Events with Significant Human Relevance: -End-Permian (≈ 252 million years ago): mass extinction caused by volcanic eruptions resulted in:

    • ~90-96% marine species and ~70% terrestrial species extinct.

    • Cretaceous (65 MYA): large asteroid impact caused a major extinction event.

    • Approximately 75% of species disappeared, marking a significant event particularly for non-avian dinosaurs.

Consequences of Mass Extinctions

  • Each mass extinction was followed by periods of adaptive radiation, diversifying life that survived.

  • Extinction events removed dominant species, leading to opportunities for evolution of new ones.

iClicker Question on Mass Extinctions

  • Question: How do these extinctions contribute to current patterns of biodiversity?

    • Extinctions allowed for new species to evolve, as those that survived adapted to fill ecological niches left vacant.

Summary of Key Long-term Effects

  • The Big Five mass extinctions shaped animal diversity in profound ways, leading to the emergence of new adaptations and increased ecological complexity.

Conclusions

  • The relationship between biotic and abiotic factors over Earth’s history has significantly influenced the evolutionary trajectory of life, culminating in the complexity we observe today. Understanding these dynamics is crucial for addressing contemporary biodiversity loss and conserving ecosystems against current threats.