Plate Activity (SL IB Environmental Systems & Societies (ESS))

• The surface of the Earth is divided into crustal, tectonic plates that have moved throughout geological time
• This has led to the creation of both land bridges and physical barriers with evolutionary consequences
• The Earth's crust is broken into 15 large tectonic plates and a number of smaller ones
• The place where the plates meet is called a plate margin

• Tectonic plates move apart, slide against each other, or collide
• Plates move apart at constructive plate margins
• Plates slide against each other at destructive plate margins
• Plates collide at collision plate margins

Tectonic plates

Constructive (Divergent) Plate Margin

• At the constructive boundary the plates are moving apart
• The Mid Atlantic Ridge is an example of a constructive plate boundary
• Volcanic eruptions and earthquakes can occur at this type of plate boundary

Constructive (divergent) plate margin

Destructive (Convergent) Plate Margin

• At a destructive (convergent) plate boundary the plates are moving together
• The denser, heavier oceanic plate subducts under the lighter, less dense continental plate
• The boundary between the Nazca plate and the South American plate is an example
• Volcanic eruptions and earthquakes can occur at this type of plate boundary

Destructive (convergent) plate margin

Collision Plate Margin

• At a collision boundary two plates of similar density move towards each other
• Neither is dense enough to subduct so the land is pushed upwards
• This forms fold mountains such as the Himalayas
• Earthquakes can occur at this type of plate boundary

Collision Boundary

Evolutionary Consequences of Tectonic Plate Movement

• Tectonic plate movement has had a profound impact on the evolution of life on Earth
• Plate movement has led to the creation of land bridges and physical barriers, and the changing distribution of continents has affected climate and food supply

Land bridges and physical barriers:

• • PlateTectonic plate movement has led to the creation of land bridges, which connect previously isolated landmasses and allow for the movement of organisms between them
  • For example, the Bering land bridge connected Asia and North America during the last ice age, allowing for the migration of animals such as mammoths and humans
  • Similarly, the formation of the Isthmus of Panama created a physical barrier between the Atlantic and Pacific Oceans, leading to the evolution of distinct marine species on either side

Climate and food supply:

• • The distribution of continents has also had a significant impact on climate and food supply, which has contributed to evolution
  • For example, the separation of Africa and South America led to the formation of the Atlantic Ocean, which created a drier climate in Africa due to reduced moisture transport
  • This led to the evolution of savannah ecosystems and the expansion of grassland habitats, which in turn influenced the evolution of grazing animals such as antelopes and zebras
  • Similarly, the movement of Antarctica to its current position has led to the formation of the Antarctic Circumpolar Current, which has had a major impact on global ocean currents and climate

Genetic isolation:

• • Tectonic plate movement has also led to the genetic isolation of populations, which can lead to the formation of new species over time
  • For example, the separation of Australia from the rest of the Gondwana supercontinent led to the evolution of unique flora and fauna, such as the marsupials and eucalyptus trees, that are found only in Australia

Conservation implications:

• • Understanding the evolutionary consequences of tectonic plate movement can inform conservation efforts
  • For example, land bridges can provide important migration routes for species, while physical barriers can lead to genetic isolation and unique evolutionary trajectories
  • Similarly, changes in climate and food supply can affect the distribution and abundance of species, highlighting the importance of protecting and restoring natural habitats

Photo by suzie maclean on Unsplash

The separation of Australia from Gondwana lead to the evolution of unique species such as kangaroos