continental drift theory

1. Structural evidence (jigsaw fit)
   • If the continents are joined, they fit together like a puzzle to form Pangaea.
   • Example:
     • South America fits into Africa.
     • North America fits into Europe.
2. Geological evidence
   • Similar rock types and structures are found on the coastal margins of separated continents.
   • Example:
     • Rocks on the West African coast match those on the East coast of Brazil in type, age, and formation.
3. Biological evidence
   • Fossil records show similarities across continents.
   • Example:
     • Similar plant and animal fossils found in South America, Africa, and India suggest they were once connected.
4. Geomorphological evidence
   • Similarities in mountain ranges.
   • Example:
     • The Alps and Atlas Mountains share similar formations and origins, indicating continental collisions.
5. Paleoclimatic evidence
   • Discovery of ancient glacial deposits in warm regions (e.g., Congo Basin).
   • Example:
     • Coal deposits beneath Antarctic ice caps indicate warmer climates in the past.
6. Paleomagnetic evidence
   • Rocks retain a record of the Earth's magnetic field.
   • Variations in magnetic orientation across continents suggest they have drifted.
7. Ocean floor spreading
   • Mid-ocean ridges show evidence of magma rising, creating new oceanic crust and pushing continents apart.

1. Failed to explain the mechanisms behind continental drift.
2. Criticized for being a meteorologist rather than a geologist.
3. Not all continents fit perfectly in the "jigsaw fit" theory.
4. Disputed evidence, such as the spread of plant remains by wind or currents.
5. Failed to explain glacial evidence in arid regions like Australia.

Key concepts

1. Combines ideas from isostasy, continental drift, and ocean floor spreading.
2. The Earth's outer shell (lithosphere) is divided into tectonic plates.

Tectonic plates

• Plates are rigid segments of varying sizes.
• Examples: Pacific Plate, North American Plate, African Plate, Indian Plate.

Plate movements

1. Driven by convection currents in the mantle.
2. Types of motion:
   • Diverging plates: Moving apart (e.g., Mid-Atlantic Ridge).
   • Converging plates: Colliding, causing uplift or subduction (e.g., Himalayas).
   • Neutral (transform): Sliding past each other (e.g., San Andreas Fault).

1. Diverging plates
   • Formation of:
     • Mid-ocean ridges.
     • Rift valleys (e.g., East African Rift Valley).
     • Volcanic islands (e.g., Iceland).
2. Converging plates
   • Formation of:
     • Fold mountains (e.g., Himalayas).
     • Trenches (e.g., Mariana Trench).
     • Volcanic arcs (e.g., Andes Mountains).
3. Neutral/transform boundaries
   • Lateral displacement of crust.
   • Example: San Andreas Fault.

1. Convection currents Heat from the Earth's interior drives mantle materials to rise and sink.
2. Upwelling of magma Magma rises at mid-ocean ridges, forming new crust.
3. Isostatic adjustment Crust adjusts to balance weight.
4. Thermal expansion Heating and cooling cause rocks to expand and contract, disturbing the crust.

1. Formation of landforms: Deep-sea trenches, mid-ocean ridges, volcanic arcs, and mountain belts.
2. Creation of new oceanic crust at divergent boundaries.
3. Development of rift valleys and associated volcanic activity.

1. Elements
   • Substances that cannot be broken down further.
   • Made up of atoms (protons, electrons, neutrons).
   • Over 100 elements are known, with 90 naturally occurring.
2. Compounds Some elements combine to form compounds (e.g., water, carbon dioxide).