11. Paleozoic Era: Mountains and Extinctions

What is the polar position hypothesis and how does it help explain when glaciations occurred?

suggests that large continental ice sheets only form when continents are located near the Earth's poles. This helps explain major glaciations in Earth’s history—such as those in the Late Ordovician-Silurian and Late Carboniferous-Permian—because continents were in polar regions during these times, allowing glaciers to form and persist.

What is the ocean basin volume hypothesis

the ocean basin volume hypothesis connects changes in sea level to tectonic shifts that alter the size and shape of ocean basins.

how does ocean basin volume hypothesis help explain changes in sea level?

When ocean basins are smaller due to continental collisions or spreading ridges, sea level rises. When the basins are larger, sea level falls. This explains long-term sea level trends in Earth’s geologic history.

Describe the three Paleozoic mountain-building events (orogenies) that built the Eastern US including this part of Virginia.

• Taconic Orogeny (500–420 million years ago): Caused by the collision of island arcs with the Laurentian craton.

• Acadian Orogeny (350–300 Ma): Another continental collision that further built the Appalachians.

• Alleghenian Orogeny (300–245 Ma): Final and largest collision during the formation of Pangaea. Formed massive mountain ranges, evidence of which still exists in the Blue Ridge and Massanutten regions of Virginia.

Describe changes in oxygen and carbon dioxide through the Paleozoic and how they are related to extinctions, ice ages, and expansion of plant life (forests) on continents.

• CO₂ Levels: Very high in the Cambrian (~18x modern levels), but dropped sharply during the Carboniferous due to forest expansion and photosynthesis.

• O₂ Levels: Rose significantly, enabling the evolution of large animals and giant insects.

• Climate Impact: Falling CO₂ contributed to ice ages and extinctions, including those in the Ordovician-Silurian and Late Devonian.

• The Permian-Triassic extinction ("Great Dying") was caused in part by massive volcanic CO₂ emissions.

What unusual organisms existed during the Cambrian Explosion?

• Hallucigenia: Spiny worm-like creature with tentacles; once thought to be upside down.

• Wiwaxia: Armored, slug-like organism.

• Opabinia: Had five eyes and a clawed proboscis.

• Anomalocaris: Large predator with eyes that had tens of thousands of lenses.
  These bizarre animals represent early experiments in body plans during a time of rapid evolutionary diversification.

Describe common fossils from the Paleozoic and the animals that created them.

• Trilobites: Marine arthropods with segmented bodies and exoskeletons; lived on sea floors.

• Brachiopods: Shelled marine animals with a foot-like structure.

• Nautiloids: Shelled swimmers, related to squids.

• Conodonts: Small eel-like creatures, known from their tooth-like fossils.

• Giant insects: Such as Arthropleurida, a millipede-like creature up to 8 feet long.
  These fossils tell us about the diverse marine and early terrestrial ecosystems of the Paleozoic.

What was the "Great Dying"?

Ordovician-Silurian, Late Devonian, and the most severe—Permian-Triassic extinction. This event wiped out about 95% of marine species and 70% of terrestrial species, likely due to massive volcanic eruptions (Siberian Traps) and the resulting CO₂-driven climate change.

How many large extinctions happened during the Paleozoic?

5