Africa Lesson 2 : Physical features

Lesson 2 Africa's Governments and Religions

Lesson 2: Plate Tectonics There are a few handfuls of major plates and dozens of smaller, or minor, plates. Six of the majors are named for the continents embedded within them, such as the North American, African, and Antarctic plates. Though smaller in size, the minors are no less important when it comes to shaping the Earth. The tiny Juan de Fuca plate is largely responsible for the volcanoes that dot the Pacific Northwest of the United States. The plates make up Earth's outer shell, called the lithosphere. (This includes the crust and uppermost part of the mantle.) Churning currents in the molten rocks below propel them along like a jumble of conveyor belts in disrepair. Most geologic activity stems from the interplay where the plates meet or divide. The movement of the plates creates three types of tectonic boundaries: convergent, where plates move into one another; divergent, where plates move apart; and transform, where plates move sideways in relation to each other. They move at a rate of one to two inches (three to five centimeters) per year. Convergent BoundariesWhere plates serving landmasses collide, the crust crumples and buckles into mountain ranges. India and Asia crashed about 55 million years ago, slowly giving rise to the Himalaya, the highest mountain system on Earth. As the mash-up continues, the mountains get higher. Mount Everest, the highest point on Earth, may be a tiny bit taller tomorrow than it is today. These convergent boundaries also occur where a plate of ocean dives, in a process called subduction, under a landmass. As the overlying plate lifts up, it also forms mountain ranges. In addition, the diving plate melts and is often spewed out in volcanic eruptions such as those that formed some of the mountains in the Andes of South America. At ocean-ocean convergences, one plate usually dives beneath the other, forming deep trenches like the Mariana Trench in the North Pacific Ocean, the deepest point on Earth. These types of collisions can also lead to underwater volcanoes that eventually build up into island arcs like Japan. Divergent Boundaries At divergent boundaries in the oceans, magma from deep in the Earth's mantle rises toward the surface and pushes apart two or more plates. Mountains and volcanoes rise along the seam. The process renews the ocean floor and widens the giant basins. A single mid-ocean ridge system connects the world's oceans, making the ridge the longest mountain range in the world. On land, giant troughs such as the Great Rift Valley in Africa form where plates are tugged apart. If the plates there continue to diverge, millions of years from now eastern Africa will split from the continent to form a new landmass. A mid-ocean ridge would then mark the boundary between the plates. Transform Boundaries The San Andreas Fault in California is an example of a transform boundary, where two plates grind past each other along what are called strike-slip faults. These boundaries don't produce spectacular features like mountains or oceans, but the halting motion often triggers large earthquakes, such as the 1906 one that devastated San Francisco.

Social Studies Quiz Lesson 11.2 Africa

Lesson 1: Continental Drift Theory and the Evidences that support the Theory Continental drift describes one of the earliest ways geologists thought continents moved over time. Today, the theory of continental drift has been replaced by the science of plate tectonics. The theory of continental drift is most associated with the scientist Alfred Wegener. In the early 20th century, Wegener published a paper explaining his theory that the continental landmasses were “drifting” across the Earth, sometimes plowing through oceans and into each other. He called this movement continental drift. Pangaea Wegener was convinced that all of Earth’s continents were once part of an enormous, single landmass called Pangaea. Wegener, trained as an astronomer, used biology, botany, and geology describe Pangaea and continental drift. For example, fossils of the ancient reptile mesosaurus are only found in southern Africa and South America. Mesosaurus, a freshwater reptile only one meter (3.3 feet) long, could not have swum the Atlantic Ocean. The presence of mesosaurus suggests a single habitat with many lakes and rivers. Wegener also studied plant fossils from the frigid Arctic Archipelago of Svalbard, Norway. These plants were not the hardy specimens adapted to survive in the Arctic climate. These fossils were of tropical plants, which are adapted to a much warmer, more humid environment. The presence of these fossils suggests Svalbard once had a tropical climate. Finally, Wegener studied the stratigraphy of different rocks and mountain ranges. The east coast of South America and the west coast of Africa seem to fit together like pieces of a jigsaw puzzle, and Wegener discovered their rock layers “fit” just as clearly. South America and Africa were not the only continents with similar geology. Wegener discovered that the Appalachian Mountains of the eastern United States, for instance, were geologically related to the Caledonian Mountains of Scotland. Pangaea existed about 240 million years ago. By about 200 million years ago, this supercontinent began breaking up. Over millions of years, Pangaea separated into pieces that moved away from one another. These pieces slowly assumed their positions as the continent we recognize today. Today, scientists think that several supercontinents like Pangaea have formed and broken up over the course of the Earth’s lifespan. These include Pannotia, which formed about 600 million years ago, and Rodinia, which existed more than a billion years ago. Tectonic Activity Scientists did not accept Wegener’s theory of continental drift. One of the elements lacking in the theory was the mechanism for how it works—why did the continents drift and what patterns did they follow? Wegener suggested that perhaps the rotation of the Earth caused the continents to shift towards and apart from each other. (It doesn't.) Today, we know that the continents rest on massive slabs of rock called tectonic plates. The plates are always moving and interacting in a process called plate tectonics. The continents are still moving today. Some of the most dynamic sites of tectonic activity are seafloor spreading zones and giant rift valleys. In the process of seafloor spreading, molten rock rises from within the Earth and adds new seafloor (oceanic crust) to the edges of the old. Seafloor spreading is most dynamic along giant underwater mountain ranges known as mid-ocean ridges. As the seafloor grows wider, the continents on opposite sides of the ridge move away from each other. The North American and Eurasian tectonic plates, for example, are separated by the Mid-Atlantic Ridge. The two continents are moving away from each other at the rate of about 2.5 centimeters (1 inch) per year. Rift valleys are sites where a continental landmass is ripping itself apart. Africa, for example, will eventually split along the Great Rift Valley system. What is now a single continent will emerge as two—one on the African plate and the other on the smaller Somali plate. The new Somali continent will be mostly oceanic, with the Horn of Africa and Madagascar its largest landmasses. The processes of seafloor spreading, rift valley formation, and subduction (where heavier tectonic plates sink beneath lighter ones) were not well-established until the 1960s. These processes were the main geologic forces behind what Wegener recognized as continental drift.

Africa Lesson 1 Pre-Lesson Assessment "Single Story"

Spanish Version Lesson 1 Social Studies The Medieval World Chapter 1 Medieval Europe The Great Fall Beginning in the 300s CE, there was great turmoil in the Western Roman Empire. After decades of invasions by Germanic tribes, the empire fell in 476 CE. At its height, the Roman Empire had reached across Europe and included northern Africa and parts of Asia. Life in the empire before it collapsed was either luxurious or simple, depending on where you were within the social order. If you were a member of the political class, you lived well. You would have enjoyed parties, lived in a large home, and had servants or enslaved persons tending to your every need. You would have attended civic gatherings in ornate government buildings. Most people, though, lived modest lives If you were at the bottom of the social structure, you would have lived in a simple home and worked hard every day. When you were not working, you might have enjoyed watching chariot races or gladiator fights. What all Romans had in common, however, was the patriarchy. This was a system in which the oldest man in a family made all the public decisions. The women were responsible for taking care of the home and the children, and they had few rights. This rigid social structure was the backbone of Roman society for centuries. Even though the fall of the empire meant that Roman government no longer existed, day-to-day life went on as before for many people. Those living far from Rome probably did not even hear about the invasions or the fall of Rome. As a result, the language and the structure of society remained largely the same—at least for some time. The ten centuries that followed the fall of the Western Roman Empire in Europe are called the Middle Ages, or the medieval period. Three important groups shaped life in medieval Europe. These were the Church, the aristocracy, and the commoners. The Church included bishops, monks, and priests, known as clergy. People were part of the aristocracy if their family were also members of this group. Aristocrats held most of the land throughout Europe and most of the Vocabulary patriarchy, n. a social structure marked by the dominance of the father in the family Vocabulary medieval, adj. relating to the Middle Ages in Europe aristocracy, n. the upper or noble class whose members’ status is usually inherited clergy, n. in a Christian church, p military and political power. The commoners included everyone who was not aristocratic or part of the Church. Commoners ranged from wealthy merchants to poor people who owned nothing. Craftspeople, merchants, traders, and bankers were all part of the middle class of commoners. The Church was the only major institution in Europe that survived the fall of the empire. Building on the influence of Emperor Constantine and the gathering of church leaders at Nicaea in 325 CE, Emperor Theodosius I had made Christianity the official religion of the Roman Empire in 380 CE. After that, the Church organized itself with a structure similar to the old Roman government, with each region having headquarters in a major city. The leader of the entire Church was the pope. The pope was, and still is, the leader of the Catholic religion throughout the world

Lesson 3 African Society and Culture

Lesson 1 The Rise of African Civilizations

Related quizzes

Related quizzes