57.1

Geological and Meteorological Activity

• Changes in ecosystem structure and dynamics are influenced by geological and meteorological events.

• Significant geological events include:

  • Continental drift: the movement of Earth's continents.

  • Ice ages: prolonged periods of cold affecting species distribution.

  • Mass extinctions: devastating losses of biodiversity.

• Important meteorological events include El Niño phenomena that affect global climates cyclically every 5 to 8 years.

Disruptions Caused by Continental Drift

• Pangaea: 250 million years ago, Earth was one supercontinent known as Pangaea.

  • By 100 million years ago, Pangaea split into Laurasia and Gondwana.

  • Laurasia formed North America, Europe, Asia; Gondwana formed South America, Africa, Antarctica, Australia.

  • The historical connections among continents help explain modern species distributions.

  • Example species distributions:

    • North America, Europe, Asia share closely related species of elk, bison, and trees (maple, oak).

    • Unique diversity of marsupials in Australia, due to long-term isolation allowed for species like kangaroos and koalas to evolve.

  • Climate Change Effects:

    • Continental drift caused changes in climates affecting ecosystem types.

    • Example: Antarctica was once near the equator, supporting lush forests; now it has a tundra ecosystem at the poles.

Disruptions Caused by Ice Ages

• Ice ages led to glaciers advancing southward into regions like Canada and parts of the U.S.

• Glaciers eliminated existing ecosystems, killing plants and animals.

• As the planet warmed, glaciers receded, uncovering land for colonization:

  • Plants with wind-blown seeds could quickly occupy bare soil.

  • Animals, like squirrels, help disperse tree seeds northward, allowing gradual tree expansions.

  • Ecological succession occurred as species slowly migrated northward.

  • Case Studies:

    • Pollen samples from lake sediments help trace the historical distribution of tree species, revealing migration patterns over thousands of years.

    • Example: Pine trees expanded their northern limit over 5000 years; hickory trees took 7000 years to shift their distributions northward.

  • Ecosystems shifted as glaciers retreated, transitioning from tundra and coniferous forests to temperate deciduous forests.

Disruptions Caused by Mass Extinction Events

• Mass extinctions, defined as events where at least 75% of species were lost within two million years, have shaped ecosystems:

  • Five significant mass extinction events occurred, driven by climatic shifts, ice ages, volcanism, and asteroid impacts.

  • Adaptation challenges faced by species during these periods led to widespread extinctions.

  • Despite an estimated 4 billion species existing over Earth's history, approximately 99% have gone extinct.

  • Examples of past extinctions include:

    • Large mammals like woolly mammoths and saber-toothed cats in North America around 12,000 years ago, likely due to a mix of human influence and climatic changes.