6.5 Tectonics

• Jigsaw: Refers to the concept of continental drift where continents appear to fit together like pieces of a jigsaw puzzle. This observation was a key piece of evidence supporting the theory of plate tectonics.
• Continental Coasts: Coastal regions situated along the edges of continents. These areas are influenced by tectonic processes such as subduction, uplift, and erosion, leading to various landforms and geological features.
• Fossil Record: Refers to the collection of preserved remains and traces of past life forms found in sedimentary rocks. In the context of tectonics, the fossil record provides valuable evidence for understanding past environments, climate, and the movement of continents over geological time scales.
• Fossils of Mesosaurus, an extinct reptile similar to a crocodile, have been discovered in parts of Africa and South America that would fit together like pieces of a jigsaw puzzle.
• 300 million-year-old fossils of the plant Glossopteris have been found in Antarctica, India, Australia, Africa, and South America, providing evidence that these continents were once connected.
• The Earth's magnetic field has experienced numerous reversals in polarity over the past 100 million years, as evidenced by changes in the direction of compass needles.
• Magnetic crystals in molten rocks align with the Earth's magnetic field and solidify in that alignment, forming a record of the magnetic field's direction over time, known as alignment.
• Mid-oceanic ridges, where magma rises from the mantle and solidifies, exhibit magnetic crystals aligned with the current north direction of the Earth's magnetic field, indicating the direction of plate movement.
• These discoveries support the theory of continental drift and plate tectonics by demonstrating that continents were once connected and have since moved apart.
• Understanding the Earth's magnetic field and its history helps scientists reconstruct past plate movements and geological events.
• Alignment of magnetic crystals in rocks provides crucial evidence for plate tectonics and continental drift theories.
• The distribution of earthquakes and volcanoes along tectonic plate boundaries supports the hypothesis of moving tectonic plates.
• Studying these phenomena helps scientists better understand the dynamic processes shaping the Earth's surface and geology.
• Mesosaurus lived approximately 275 million years ago.
• The fossils of Glossopteris date back to around 300 million years ago.
• The Earth's magnetic field has experienced polarity reversals for at least the last 100 million years.
• The alignment of magnetic crystals in rocks provides a record of the Earth's magnetic field at the time of solidification.
• The study of mid-oceanic ridges and their magnetic alignment helps determine the age and movement of tectonic plates.
• Fossil discoveries and geological evidence provide insights into the past positions and movements of continents.
• Analysis of magnetic crystals in rocks helps reconstruct the history of the Earth's magnetic field and plate movements.
• The alignment of magnetic crystals is measured and analyzed to determine the orientation of the Earth's magnetic field at various points in geological history.
• Observations of mid-oceanic ridges and their magnetic alignment provide evidence for seafloor spreading and plate movement.
• 1. Monitoring seismic activity and volcanic eruptions along tectonic plate boundaries helps confirm the movement of tectonic plates.
• Plate tectonics is a scientific theory that explains how major landforms are created as a result of Earth's subterranean movements. The theory, which solidified in the 1960s, transformed the earth sciences by explaining many phenomena, including mountain building events, volcanoes, and earthquakes.
• Below the lithosphere is the asthenosphere — a viscous layer kept malleable by heat deep within the Earth. It lubricates the undersides of Earth's tectonic plates, allowing the lithosphere to move around. 
• The driving force behind plate tectonics is convection in the mantle. Hot material near the Earth's core rises, and colder mantle rock sinks. 
• Due to the convection of the asthenosphere and lithosphere, the plates move relative to each other at different rates, from two to 15 centimeters (one to six inches) per year.
• This interaction of tectonic plates is responsible for many different geological formations such as the Himalaya mountain range in Asia, the East African Rift, and the San Andreas Fault in California, United States.
•  a supercontinent he called Pangaea began to break into pieces, its parts moving away from one another. The continents we see today are fragments of that supercontinent. To support his theory, Wegener pointed to matching rock formations and similar fossils in Brazil and West Africa. In addition, South America and Africa looked like they could fit together like puzzle pieces.
• Transform boundaries:

  These boundaries happen where two lithospheric plates move apart, or maybe further precisely, collide away from one other despite the transform faults, where plates are neither created nor destroyed.
• Divergent boundaries:

  These boundaries happen when both plates move apart from one another.
• Convergent boundaries:

  These boundaries happen when both plates move towards one other to form a zone of subduction or a continental collision.
• Transform boundaries:

  These boundaries happen when natural or human-made structures that cross a transform boundary are offset—split into pieces and carried in opposite directions.
• Plate boundary zones:

  These boundaries happen where the effects of the interactions are unclear, and the boundaries usually occur along a broad belt.
• The Earth's mantle, heated by the inner core reaching temperatures over 5000°C, receives thermal energy from various sources such as residual heat from Earth's formation and friction within the planet's layers. Thermal energy transfer occurs through convection currents in the mantle, driven by the expansion and upward movement of heated mantle material and its subsequent cooling and sinking. These convection currents slowly move the Earth's tectonic plates, which make up the crust, at rates ranging from 0.6 to 10 cm per year.
• Volcanoes:

  1. Formation: Volcanoes form when molten rock (magma), gas, and ash escape to the Earth's surface through openings called vents or fissures. This typically occurs at convergent plate boundaries, where tectonic plates collide or move apart, allowing magma to rise.
  2. Magma Composition: The type of volcano formed depends on the composition of the magma. Magma with high silica content tends to produce explosive eruptions and steep-sided volcanoes (stratovolcanoes), while magma with low silica content flows more easily and forms gentle-sloped shield volcanoes.
• Volcanoes:

  1. Eruption: When pressure from gases within the magma chamber becomes too great, it causes an eruption. Explosive eruptions release ash, gas, and lava fragments, while effusive eruptions produce flowing lava.
  2. Subduction Zones: Volcanoes also form at subduction zones, where one tectonic plate is forced beneath another, creating magma through the partial melting of the descending plate.
• Earthquakes:

  1. Formation: Earthquakes occur due to the sudden release of energy along faults in the Earth's crust. Most earthquakes are caused by the movement of tectonic plates, which build up stress along faults until it exceeds the strength of the rocks, resulting in sudden movement.
• Earthquakes:

  1. Faults: Faults are fractures in the Earth's crust along which movement has occurred. The main types of faults are strike-slip, where movement is horizontal; normal faults, where the hanging wall moves downward relative to the footwall; and reverse faults, where the hanging wall moves upward relative to the footwall.
  2. Focus and Epicenter: The point within the Earth where an earthquake originates is called the focus or hypocenter. The point on the Earth's surface directly above the focus is called the epicenter.
• Earthquakes

  1. Seismic Waves: When an earthquake occurs, it generates seismic waves that travel through the Earth's interior. The two main types of seismic waves are body waves (P-waves and S-waves) and surface waves.
  2. Magnitude: Earthquakes are measured using the Richter scale or moment magnitude scale, which quantifies the energy released during an earthquake.