Climate change

Learning Objectives

1. Describe changes in climatic conditions over geologic time

2. Explain the evidence for climate change today relative to historical records of temperature and carbon dioxide concentrations

3. Explain how climate conditions and the movement of continents select for the traits of organisms over geologic time

4. Use the movement of continents to explain the current distribution of fossils and living organisms

5. When provided with a phylogenetic tree with specific evolutionary milestones, use evidence to place an unknown organism with specific, given traits on the phylogenetic tree of life and within the geologic time scale

6. Identify whether a group is monophyletic or non-monophyletic and whether a shared trait is homologous or analogous

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🌍 Major Climate Events & Their Evolutionary Impact

❄ Snowball Earth (~600 MYA)

• Earth experienced several global glaciations during the Proterozoic Eon.

• Causes:

  • Equatorial continents → increased albedo (light reflection).

  • Cyanobacteria boom → oxygen reacted with methane → reduced greenhouse gases.

• Consequences:

  • Glaciation may have set the stage for later oxygenation and evolutionary radiations.

🌬 Oxygenation of the Atmosphere ("Great Oxidation Events")

🦠 ~2.5 BYA — First Oxygenic Photosynthesis (Cyanobacteria)

• O2 produced in oceans → reacted with iron → formed banded iron formations.

• Led to mass extinction of anaerobic organisms (“oxygen catastrophe”).

🧬 1.6–2 BYA — First Eukaryotes

• Oxygen enabled aerobic respiration, leading to more energy-efficient life.

🌐 ~600–542 MYA — O2 Accumulated in Atmosphere

• Saturation of O2 sinks → O2 gas built up.

• Formation of ozone layer → protection from UV radiation.

• Led to Cambrian explosion and multicellular diversification.

🌡 Temperature and Sea Level Fluctuations

🔁 Temperature Cycles:

• Earth has naturally fluctuated between hothouse and icehouse states.

• Phanerozoic Eon (542 MYA–present): alternating warm and glacial periods.

🌋 Natural Climate Drivers:

• Milankovitch cycles (orbital changes).

• Volcanic eruptions (cooling due to aerosols).

• Solar intensity changes.

🏭 Anthropocene and Modern Climate Change (Post-1950s)

⚠ Drivers:

• Fossil fuel combustion, deforestation, agriculture.

• Sharp rise in CO₂ from 280 ppm (pre-industrial) to 425 ppm (2025).

🔍 Evidence:

• Ice cores (CO₂ and temperature correlation).

• Glacier retreat, sea level rise, altered species distributions.

🧠 Key Point:

🧬 Climate as a Selective Pressure in Evolution

🔹 Examples:

• Oxygen Revolution → Rise of aerobic organisms.

• Drying of Earth → Favored seed plants and amniotes.

• Modern rapid climate change → Mismatches in pollination timing, habitat shifts, etc.

🌍 Continental Drift & Supercontinents

🧩 Supercontinents Over Time:

🔄 Supercontinent Cycle:

• Aggregation and rifting every 300–500 million years.

• Influences climate, sea level, biogeography, and evolution.

🦴 Fossil Evidence & Biogeography

• Continental drift explains fossil similarities on distant continents.

• Example: Similar fossils in South America and Africa make sense if they were once connected (Pangaea).

🧭 Placing Unknown Organisms in Geologic Time

🧬 Use Traits + Timing:

• Tetrapod with five digits? Appeared in late Devonian (~360 MYA).

• Mammal? Arose in Mesozoic, diversified in Cenozoic.

• Flowering plant? Diversified in Cretaceous.

🌟 Final Thoughts: Climate Drives Evolution

• Climate change isn’t just a modern concern — it’s been a central force shaping life on Earth.

• Evolution occurs as selective pressures change.

• Understanding past changes helps us predict and prepare for future biodiversity challenges.