Backup Scinece notes.docx

6/2/25 Plate Tectonics - We have 10 major tectonic plates on earth - Said plates 'float' on top of the mantle and so can move oround the earth's surface. - According to contenential drift theory, the crust works lika a jigsaw made of the tectonic plates - Australia is on the oce...

6/2/25 Plate Tectonics - We have 10 major tectonic plates on earth - Said plates 'float' on top of the mantle and so can move oround the earth's surface. - According to contenential drift theory, the crust works lika a jigsaw made of the tectonic plates - Australia is on the oceanic plate - Convection: A process by which heat is transferred by movement of a heated fluid/liquid - Movement of the plates can be disastrous, as earthquakes and or volcanoes occur at the edegs 10/02/2025 - Oceanic plates are denser than continental plates - At a divergent boundary, where two plates are separating from each other, a moid ocean ridge is formed. This is where the seafloor spreads and new iceanic olates is made. **Earthquakes can occur at these plates** - At a **continent-continent divergent plate boundary**, two continental plates move **away from each other** due to **tensional forces** in the Earth\'s lithosphere. This process leads to the formation of a **rift valley**, which can eventually develop into a new ocean basin if divergence continues. - **Key Processes at a Continent-Continent Divergent Boundary** - **Rifting Begins** - The Earth\'s crust stretches and becomes thinner. - Large faults (cracks) form, and blocks of crust drop down, creating a **rift valley**. - Magma rises, causing volcanic activity. - **Formation of Rift Valleys** - As the plates pull apart, deep valleys form, often filled with lakes and volcanic activity. - Earthquakes are common due to fault movements. - **New Ocean Formation (If Rifting Continues)** - If the rifting continues for millions of years, the valley may sink below sea level, allowing ocean water to flood in. - This eventually forms a new ocean basin (like how the **Atlantic Ocean** formed from the separation of Pangaea). - **Examples of Continent-Continent Divergent Boundaries** - **East African Rift Valley** -- Currently splitting the African Plate into two smaller plates (the Nubian and Somali plates). - **Iceland\'s Mid-Atlantic Rift** -- A visible part of the Mid-Atlantic Ridge where the Eurasian and North American plates are moving apart. - **Key Features of Continent-Continent Divergent Boundaries** - ✔ **Rift Valleys** (low-lying areas with faults)\ ✔ **Volcanic Activity** (due to rising magma)\ ✔ **Earthquakes** (caused by the stretching and breaking of the crust) - At a convergent boundary, the two plates buckle and create mountains - This collision cause a subduction zone to be created and create mountains chains, trenches and can cause volcanoes and earthquakes. 11/02/2025 Earthquakes - An earthquake is a vibration and/or the trembling f the ground that may cause the folding or breaking of rocks - A fault is a break in the rock along which movement has occurred - Earthquakes normally occur near plate boundaries - They can occur by Pushing against in each other at a subduction zone. - Spreading apart to form ocean ridges and new underwater volcanoes or volcanic islands. - The focus is the point of origin in an earthquake - The epicentre is where the focus point is on the ground - Seismic waves are the vibrations caused by the movement of rocks and start at the focus. - P waves are primary waves that travel through both solid and liquids, and are the fastest of all the waves - S waves come after the P waves and can only travel through solids. - L waves are the most catastrophic and slow waves compared to the other two. they travel around the world and are the last one detected. - Convection currents from the mantle push two tectonic plates agaimst each other - The Richter scale measures the earthquakes magnitude **Seafloor Spreading and Magnetic Striping** **Seafloor Spreading** - Proposed by **Harry Hess** in the 1960s as part of **plate tectonics theory**. - Seafloor spreading occurs at **mid-ocean ridges**, where magma rises from beneath the Earth\'s crust. - As magma cools, it forms **new oceanic crust**, which pushes the older crust away from the ridge. - This movement causes the **ocean floor to widen** over time. - Older rock is found **farther from the ridge**, while newer rock is **closer to the ridge**. - The process explains why continents move (continental drift). **Magnetic Striping (Paleomagnetism)** - As magma cools and solidifies, **iron-rich minerals** in the rock align with Earth\'s magnetic field. - Earth\'s magnetic field **reverses** every few hundred thousand years, switching between **normal polarity** (north is north) and **reversed polarity** (north is south). - These changes create **magnetic stripes** on either side of the mid-ocean ridge, forming a **mirror image** pattern. - Scientists use these stripes to **determine the age of the seafloor** and prove that new crust is continuously forming. **Evidence for Seafloor Spreading** 1. **Age of Rocks** -- The youngest rocks are near mid-ocean ridges, and the oldest rocks are farther away. 2. **Magnetic Striping** -- Symmetrical patterns of magnetism on either side of the ridge match Earth\'s historical magnetic reversals. 3. **Earthquake and Volcano Activity** -- Most occur at mid-ocean ridges and subduction zones, supporting the idea of moving plates. **Real-World Examples** - **Mid-Atlantic Ridge** (between North America and Europe/Africa) - **East Pacific Rise** (in the Pacific Ocean) **Why It's Important** - Explains how continents move (plate tectonics). - Helps scientists understand Earth's history and predict geological events. - Provides evidence for the theory of plate tectonics, which describes the movement of Earth\'s lithosphere.