Chapter 4 Plate Tectonics

Wegener called the single large landmass Pangaea. This term refers to the supercontinent that existed millions of years ago, before it eventually broke apart and formed the continents we know today. Pangaea was a concept proposed by Wegener as part of his theory of continental drift, which suggested that the continents were once joined together and have since moved apart.

The Earth is made up of several layers. These layers include the inner core, outer core, mantle, and crust. The inner core is a solid ball of iron and nickel, while the outer core is a liquid layer. The mantle is made up of solid rock, and the crust is the outermost layer that we live on. These layers have different compositions and properties, and they play a crucial role in shaping the Earth's structure and geologic processes.

Tectonic plates are large pieces of the Earth's lithosphere that move and interact with each other. These plates are made up of two types of crust: continental crust and oceanic crust. Continental crust is the thicker and less dense type of crust found beneath landmasses, while oceanic crust is thinner and denser, found beneath the ocean floor. The interaction between these two types of crusts plays a significant role in shaping the Earth's surface through processes like plate tectonics, volcanic activity, and earthquakes.

Tectonic plates fit together like a jigsaw puzzle because they have irregular edges that interlock with each other. Just like the pieces of a jigsaw puzzle, tectonic plates have specific shapes that fit together perfectly. This fitting allows the plates to move and interact with each other along their boundaries, causing phenomena such as earthquakes and the formation of mountains. The analogy of a jigsaw puzzle accurately represents the complex and interconnected nature of tectonic plate movements.

Seismic waves are caused by earthquakes. When there is a sudden release of energy in the Earth's crust, it creates vibrations that travel through the Earth's layers, resulting in seismic waves. These waves can be classified into two types: body waves and surface waves. Body waves, including P-waves and S-waves, travel through the Earth's interior, while surface waves move along the Earth's surface. Earthquakes are the primary cause of seismic waves, as they generate the necessary energy and motion to propagate these waves.

Uplift refers to the geological process in which parts of the Earth's crust rise. This can occur due to various factors such as tectonic activity, volcanic eruptions, or the erosion of overlying materials. During uplift, the crust is pushed upwards, leading to the formation of mountains, plateaus, or other elevated landforms. This process is essential in shaping the Earth's surface and can have significant impacts on the environment and the distribution of land and water.

Stress refers to the amount of force or pressure exerted on an object or material. It is the measure of the internal resistance of a material to deformation under an applied force. Stress can cause changes in shape, size, or volume of an object, and it is an important factor in determining the strength and stability of structures.

A transform boundary is a type of boundary between tectonic plates where they slide past each other horizontally. This movement can cause earthquakes as the plates grind against each other. Unlike convergent boundaries where plates collide or divergent boundaries where plates move apart, a transform boundary does not involve the creation or destruction of crust. Instead, it is characterized by the lateral movement of the plates, making it the correct answer in this case.

Volcanic mountains are formed when magma rises to Earth's surface and erupts. This process occurs at divergent plate boundaries, where tectonic plates move apart, allowing magma to reach the surface through volcanic activity. The magma, which is molten rock, erupts as lava, ash, and gases, building up layers of solidified volcanic material over time. This accumulation of volcanic material forms a cone-shaped mountain. Examples of volcanic mountains include Mount St. Helens in the United States and Mount Fuji in Japan.

The correct answer is sea-floor spreading. This discovery provided evidence for the movement of continents and supported Wegener's hypothesis of continental drift. Sea-floor spreading occurs at mid-ocean ridges, where new oceanic crust is formed and pushes older crust away. This process creates a symmetrical pattern of magnetic anomalies on either side of the ridge, indicating that the oceanic crust is moving away from the ridge. This evidence strongly supported the idea that continents were also moving and provided a mechanism for how it could occur.

Seismic waves are the correct answer because they are used to map the deep interior of the Earth. Seismic waves are generated by earthquakes or artificially created by explosions, and they travel through the Earth's layers. By analyzing the behavior of these waves as they travel through different materials, scientists can gather information about the composition and structure of the Earth's interior. This technique, known as seismic tomography, has provided valuable insights into the Earth's core, mantle, and crust. Sonar is used to map underwater features, drilling expeditions provide information about the Earth's crust, and ocean waves are not suitable for mapping the deep interior of the Earth.

A divergent boundary is a boundary between tectonic plates that move away from each other. This movement causes the plates to separate and create a gap in the Earth's crust. As the plates move apart, magma from the mantle rises to fill the gap, creating new crust. This process is known as seafloor spreading and can lead to the formation of new oceanic crust and features such as mid-ocean ridges.

Subsidence is the correct answer because it refers to the sinking of parts of Earth's crust. This can occur due to various factors such as the withdrawal of underground fluids, the collapse of underground caves, or the tectonic movement of plates. Subsidence can result in the formation of sinkholes, the lowering of land levels, and the flooding of coastal areas.

A fault block that you could rest a foot on is called the footwall. In a fault, the footwall is the block of rock that lies below the fault line. It is called "footwall" because it is the lower portion of the fault block, and if you were standing on the fault, you could rest your foot on it. The hanging wall, on the other hand, refers to the block of rock that lies above the fault line.

The correct answer is magnetic reversal. This refers to the process where the Earth's magnetic poles switch places. Over time, the Earth's magnetic field can weaken and flip, causing the north and south magnetic poles to interchange. This phenomenon has occurred multiple times throughout Earth's history and is recorded in rocks and sediments, providing evidence of these magnetic reversals. Continental drift, magnetic minerals, and fossils are not directly related to the process of magnetic pole reversal.

A place where tectonic plates touch is called a boundary. This is where two plates meet and interact with each other. These boundaries can be classified into three types: convergent, divergent, and transform boundaries. At convergent boundaries, plates collide with each other, causing intense geological activity such as earthquakes and the formation of mountain ranges. Divergent boundaries occur when plates move apart, leading to the creation of new crust through volcanic activity. Transform boundaries involve plates sliding past each other horizontally, resulting in earthquakes. Therefore, "boundary" is the correct answer as it accurately describes the location where tectonic plates interact.

A fault is the correct answer because it refers to the surface along which rocks break and slide past each other. Faults occur due to tectonic forces that cause the Earth's crust to deform, resulting in fractures and movement along these fractures. This movement can be vertical, horizontal, or a combination of both. Faults are essential in understanding the geology of an area and can lead to the formation of mountains, earthquakes, and the displacement of rock layers.

Tectonic plates are large pieces of lithosphere that move on top of the asthenosphere. They are responsible for the movement and formation of continents, as well as the occurrence of earthquakes, volcanic activity, and the creation of mountain ranges. These plates interact with each other at their boundaries, causing various geological phenomena. The term "mantle pieces" is not accurate as the lithosphere is composed of both the crust and the uppermost part of the mantle. "Crust plates" and "puzzle pieces" are not scientifically recognized terms for describing tectonic plates.

Compression is the correct answer because stress that occurs when something is squeezed or pressed together is known as compression. This type of stress causes objects to shorten or become denser. When external forces act on an object from opposite directions, it leads to compression.

When something is stretched, stress occurs, and this type of stress is known as tension. Tension is the force that acts to stretch or elongate an object or material. It is the opposite of compression, which is the stress that occurs when something is squeezed or pressed together. Convergent and divergent are not related to stress caused by stretching, so they are not the correct answers.

When rock cools, it contracts and becomes denser. This increased density causes the rock to sink. As the rock cools, the molecules within it slow down and come closer together, resulting in a decrease in volume. This decrease in volume causes the rock to sink due to its increased density compared to the surrounding material.

Faults and folds can become mountain ranges. Faults are fractures in the Earth's crust where rocks on either side have moved relative to each other. When rocks are subjected to intense pressure and stress, they can fold and buckle, forming folds. Over time, the accumulation of these faults and folds can create large-scale deformations in the Earth's crust, resulting in the formation of mountain ranges.

The hanging wall refers to the block of rock that is located above a fault line. In this context, it is the block of rock that could be hung from on a rope. The hanging wall is typically the side of the fault that moves downward relative to the footwall during a fault slip.

An anticline is a type of rock layer fold that appears as an arch. It is characterized by the upward folding of rock layers, with the oldest rocks located at the core of the fold. This folding occurs due to compressional forces in the Earth's crust, causing the rocks to bend and buckle. The shape of an anticline resembles that of an arch, with the limbs dipping away from the center. This type of fold is commonly found in mountainous regions and is important in geology for understanding the structure and formation of the Earth's crust.

When rock is heated, it undergoes thermal expansion, causing it to expand and become less dense. This decrease in density causes the heated rock to rise, as it becomes lighter than the surrounding cooler rock. This phenomenon is commonly observed in geology, where heated magma rises and forms volcanic eruptions.

A normal fault occurs when the hanging wall moves downward relative to the footwall. This type of fault is caused by tensional forces that stretch or pull apart the Earth's crust. As a result, the hanging wall drops down relative to the footwall. This can create a steep slope or escarpment. Normal faults are commonly found in areas undergoing extension or where the Earth's crust is being pulled apart, such as along divergent plate boundaries or in rift zones.

Scientists use global positioning systems (GPS) to measure tectonic plate movement. GPS technology allows scientists to track the precise locations of different points on the Earth's surface. By monitoring these points over time, scientists can determine how the plates are moving and measure the speed and direction of their movement. GPS provides accurate and real-time data, making it an essential tool for studying tectonic plate movement and understanding the dynamics of the Earth's crust.

A rock layer fold that looks bent in the middle is called a monocline. In a monocline, the layers of rock are folded in a downward direction on one side, creating a step-like structure. This type of fold usually occurs due to tectonic forces pushing the rock layers from one side, causing them to bend and fold. Monoclines are commonly found in areas with significant geological activity, such as mountain ranges or regions with active faulting.

The breakup of Pangaea is the correct answer because it provides evidence for sea-floor spreading. Pangaea was a supercontinent that existed about 300 million years ago and eventually broke apart into separate continents. As the continents moved apart, new oceanic crust formed at the mid-ocean ridges, causing the sea floor to spread. This process can be observed through magnetic minerals on the ocean floor, which align with the Earth's magnetic field and create magnetic stripes. The fossils found in South America and Africa also support this theory, as they show similarities between species that were once connected before the continents separated.

When plates move along a transform boundary, they slide past each other horizontally. This movement can cause tension and stress to build up along the boundary. As the stress becomes too great, it is released in the form of earthquakes. Sea-floor spreading is another possible result of plates moving along a transform boundary. This occurs when two plates are moving in opposite directions and new oceanic crust is formed as magma rises to fill the gap between them. Therefore, sea-floor spreading is a valid explanation for the given question.