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Out of africa theory
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Continental Drift Theory. From the discussion of the rock cycle, it has been pointed out that through Earth's external and internal processes. Earth's surface is constantly changing. However, this idea of a changing environment did not conform with the belief of earlier scientists. Rather, they thought that the geographic positions of ocean basins and continents have been static since the beginning of time. It was around the 1500s when Leonardo da Vinci, upon his discovery of fossil seashells found at the high mountains of Italy, first thought of the idea that the areas where mountains are located may have been oceans in the past. Through time, other fossils of marine organisms found far above the current sea level further supported the idea that mountains were uplifted and weathering wore them down. At around the 1800s, most scientists have accepted the idea that Earth's crust is undergoing large vertical movements or uplifting. There was also evidence of possible horizontal movements, but the scientists then were not convinced about it. Alfred Wegener showed evidence of horizontal or lateral movement of the continents in his continental drift theory. According to him, the continents have drifted around the world and have once formed a giant landmass or supercontinent called Pangaea. To support his theory, Alfred Wegener presented a set of geographical, biological, and climatic evidence.Wegener's geographical evidence included the jigsaw puzzle fit of the current continents. He pointed out that the coastlines of South America and Africa seem to fit together. He also pointed the presence of mountain ranges having similar rock types and age but separated by vast oceans, like that of the folded rocks of the Caledonian mountains. The same folded rocks run through West Africa, North America, Newfoundland, Ireland, Wales, Scotland, Greenland, and Norway, all of which are now separated by the Atlantic Ocean. A geographical evidence on the similar rock types in West Africa, North America, Greenland, and Europe is found. The biological evidence came in the discovery of similar plant and animal fossils in different continents separated by oceans. The animal fossils of Mesosaurus and Lystrosaurus indicate that they were not capable of crossing the oceans to reach the other continents. If they were, the fossils should have been more widely distributed Africa, Australia, India, and South America were too large to be carried by wind. This indicates that the areas where the fossils were found were closely linked. It has also been found out that the plant only grew in areas with subpolar climate, which would indicate that the landmasses were located near the South Pole.Lastly, for his climatic evidence, Wegener discovered that a glacial period occurred during the late Paleozoic era in Southern Africa, South America, Australia, and India. The initial explanation for this event was global cooling, but it was rejected because large tropical swamps with so much vegetation were found at the same time in the Northern Hemisphere. This further supported the idea that the supercontinent was indeed near the South Pole, and the continents in Northern Hemisphere were once near the equator. The glacial period also left glacial striations, or the scratches glaciers make as they move across on the underlying bedrock, on the aforementioned continents. For such an event to happen, the continents would have to be connected. SCIENCE PIONEER. Alfred Wegener (1880-1930). Alfred Wegener was a German polar researcher, geophysicist, and meteorologist. He was known for his work on the continental drift theory. In his effort to defend his work, he went to the Greenland ice sheet where he died.Even with all the compelling evidence, the continental drift theory hardly convinced the scientific community at that time because Wegener was unable to identify a credible mechanism that drives the continental drift. He was unable to clearly explain how the continents moved and how the larger continents broke through the ocean floor. Eventually, critics of the continental drift began to accept the theory when new evidence supporting the theory was discovered. The new evidence led to a more encompassing theory the theory of plate tectonics. This theory provided a more convincing explanation as to how the continents moved. The evidence that paved the way for the theory of plate tectonics was the idea of wandering poles. Scientists began studying volcanic rocks to determine the location of the magnetic poles. When volcanic rocks crystallize, the minerals with magnetic properties align themselves parallel to Earth's magnetic field at the time the minerals were formed. This finding allowed scientists to determine the polarity of Earth's magnetic field and the magnetic inclination that showed the location of the poles. Upon studying the paleomagnetism of the rocks, geophysicists found out that rocks from various locations point to different magnetic north poles, suggesting that the poles have wandered. Since movement of magnetic poles is very unlikely, scientists have accepted the idea that the continents are indeed moving. And if the continents are moving, scientists thought that maybe the ocean basins are moving too. They also discovered that some rocks showed magnetic reversals, which led them to believe that the magnetic north pole now was not always the magnetic north pole. Seafloor Spreading. After World War II, exploration on the ocean floor became the focus of many geologic studies. It was only then that the ocean ridge system was discovered. A geologist in Princeton University named Harry Hess, along with other scientists, studied this ocean ridge system and hypothesized that the oceanic crust was moving away from the ridge. His hypothesis, known as seafloor spreading, showed that the ocean floor is split along the ridge where the magma rises to form the new ocean floor.Because of this, rocks located near the ridge are younger than those that are located magnetic polarity of Earth is also preserved in those rocks. Withe ridge scientists were able to see the magnetic reversals in the ocean floor, and they were able to make use of information to determine that the ocean floor is moving at a rate of about 10 cm per year. Plate Tectonics. Confirmation of the seafloor spreading hypothesis proved that continents are not moving above the ocean floor. Rather, it is the fragments of the lithosphere. The lithosphere is the rigid layer that is composed of the uppermost mantle and the crust that carry the continents and the ocean basins along. These fragments of the lithosphere are called plates. Underneath the lithosphere is a weaker region in the mantle known as asthenosphere that behaves like a fluid. Thus, the lithosphere floats above the asthenosphere, making it detached and free to move. This became the basis of the theory of plate tectonics. Now that it has been made clear that it is the plates which are moving, the question as to how they move remained. Sir Arthur Holmes proposed the driving force for this plate movement in 1919. He suggested that the movement in the mantle carries the plates along. It was previously discussed that Earth's interior is very hot due to the heat produced by radioactive decay. Convection takes place in the mantle, keeping the asthenosphere hot and weak. The convection currents produced in the asthenosphere are the ones carrying the lithospheric plates and making them move. However, convection currents are not enough. Mechanisms such as ridge push and slab pull aid the convection currents to slowly move the lithospheric plates. Ridge push occurs at mid ocean ridges which are higher in elevation than the surrounding trenches and abyssal plains. The new ocean floor from the ridge is hot and relatively thin. As it moves away from the ridge, it cools down and gets denser, heavier, and thicker. Below this cooling ocean floor is the asthenosphere, which is less dense. This area becomes a massive shear zone and the new ocean floor will effectively slide down the slope of the asthenosphere. When the plate collides with another plate with lesser density, the denser plate sinks and a subduction zone is formed. When the subducting plate sinks, it pulls on the rest of the plate behind it. These mechanisms explain the movement of the plates.Earth has seven major lithospheric plates that account for 94% of Earth's surface. These are the North American Plate, South American Plate, Pacific Plate, African Plate, Eurasian Plate, Indo-Australian Plate, and Antarctic Plate. These plates are constantly moving relative to the other plates. Thus, the interaction of plates occurs mostly along the boundaries. These movements are plotted using information from earthquakes and volcanic activities. There are three main types of plate boundaries: convergent, divergent, and transform boundaries Convergent boundaries are boundaries where two plates move towards each other A convergent boundary is also known as destructive margin since this is where the collision between two plates occhins. There are three types of convergence-oceanic oceanic, oceanic-continental, and continental-continental. Trenches are features of the ocean floor that are present in both oceanic-oceanic boundary and oceanic-continental boundary. Subduction occurs at the trenches, therefore, these are characterized as the deepest parts of Earth. A divergent boundary is the opposite of convergent boundary: two plates move away from each other. Divergent boundaries create new crust; thus, they are also known as constructive margins. The ocean ridge system is a divergent boundary where new ocean floor is produced as magma rises, pushing the older rocks aside.Transform boundary is also known as conservative plate margin since two plates just move past one another, neither creating nor destroying land. Earthquake epicenters are usually detected at transform boundaries because the rocks tend to break and not fold or sink, like in convergent boundaries. Evolution of the Ocean Basins. Both the movement of the plates and seafloor are responsible for the evolution of ocean basins. Along the divergent boundary where ocean ridge systems are found, magma is released and new ocean floor is created. Along convergent boundaries, the ocean floor is being destroyed. The evolution of the ocean basins started during the time when Pangaea was still present and was surrounded by the vast ocean or superocean known as Panthalassa, also called Paleo-Pacific or "old Pacific." Upon the initial break up of Pangaea into Laurasia and Gondwanaland, the Tethys Sea began to form. Then, the Eurasian and North about, forming the North Atlantic. The South Atlantic only started to form when the African Plate and South American Plate separated. The continued movement of the plates created the Himalayas at one side and separated the Pacific Ocean and Atlantic Ocean at the other side, which consequently formed the current ocean basins. Both the movement of the plates and seafloor are responsible for the evolution of ocean basins. Along the divergent boundary where ocean ridge systems are found, magma is released and new ocean floor is created. Along convergent boundaries, the ocean floor is being destroyed. The evolution of the ocean basins started during the time when Pangaea was still present and was surrounded by the vast ocean or superocean known as Panthalassa, also called Paleo-Pacific or "old Pacific." Upon the initial break up of Pangaea into Laurasia and Gondwanaland, the Tethys Sea began to form. Then, the Eurasian and North about, forming the North Atlantic. The South Atlantic only started to form when the African Plate and South American Plate separated. The continued movement of the plates created the Himalayas at one side and separated the Pacific Ocean and Atlantic Ocean at the other side, which consequently formed the current ocean basins.Continents do not immediately end at the point where the ocean meets the land. They may extend slightly into the oceans. The portion of the continent that is submerged is called continental margin. There are two types of continental margin: passive margin and active margin. A passive continental margin consists of a continental shelf, continental slope, and continental rise. It is not associated with plate boundaries; thus, there are very little tectonic activities. An active continental margin only has a continental shelf and a continental slope. It is associated with plate boundaries; thus, a main feature of this boundary is a trench. The different features of a continental margin are the following: 1. The continental shelf is the gently-sloping submerged portion of the continent. 2. The continental slope is the steep slope after the continental shelf. It is still part of the continent. 3. The continental rise is the gently-sloping area after the continental slope and before the ocean floor. 4. The trenches are the deepest parts of the ocean. These are narrow depressions caused by the subduction of the ocean floor along the convergent boundaries. 5. The mid-oceanic ridge is the mountain range system in the ocean. It is responsible for the production of new ocean floor. This is the region where new magma constantly emerges from. SCIENCE CAREER. A scientific illustrator uses art to inform and communicate complex details and concepts of science. He/She makes use of scientifically informed observations and research along with his/her technical art and aesthetic skills to make accurate representations. In Natural History, the scientific illustrators recreate how the extinct species look like by working with scientists and fossil records. Moreover, with the advances in technology, illustrators are now into 3D modelling, animation, and video making. Earth's History. All the processes that have been discussed require long periods of time to create a noticeable change on Earth's surface. You can just imagine how long it would take to create an oceanas vast as the Pacific Ocean if the ocean floor moves only at about 10 cm/year. It is then important to know the history of Earth to learn the complexities of its past and be able to use it to understand the present. Just like learning the history of a country that requires one to read a lot of books, learning the history of Earth involves studying a lot of rocks. Rocks, especially sedimentary rocks, contain a lot of information about Earth's past. It holds the key to most of the geologic processes that happened on Earth and the key to uncovering how life on Earth evolved. But these discoveries are worthless if there is no time perspective. Thus, one of the most important contributions of geologists to mankind is the geologic time scale, which holds a history that is exceedingly long.What Is Rhythm in Music? Rhythm is the pattern of sound, silence, and emphasis in a song. In music theory, rhythm refers to the recurrence of notes and rests (silences) in time. When a series of notes and rests repeats, it forms a rhythmic pattern. In addition to indicating when notes are played, musical rhythm also stipulates how long they are played and with what intensity. This creates different note durations and different types of accents.Why Is Rhythm Important in Music? Rhythm functions as the propulsive engine of a piece of music, and it gives a composition structure. Most musical ensembles contain a rhythm section responsible for providing the rhythmic backbone for the entire group. Drums, percussion, bass, guitar, piano, and synthesizer may all be considered rhythm instruments, depending on the context. However, all members of a music group bear responsibility for their own rhythmic performances and play the musical beats and rhythmic patterns indicated by the piece's composer.7 Elements of Rhythm in Music Several core elements comprise the fundamentals of musical rhythm. 1. Time signature: A musical time signature indicates the number of beats per measure. It also indicates how long these beats last. In a time signature with a 4 on the bottom (such as 2/4, 3/4, 4/4, 5/4, etc.), a beat corresponds with a quarter note. So in a 4/4 time (also known as "common time"), each beat is the length of a quarter note, and every four beats form a full measure. In 5/4 time, every five beats form a full measure. In a time signature with an 8 on the bottom (such as 3/8, 6/8, or 9/8), a beat corresponds with an eighth note. 2. Meter: Standard Western music theory divides time signatures into three types of musical meter: duple meter (where beats appear in groups of two), triple meter (where beats appear in groups of three), and quadruple meter (where beats appear in groups of four). Meter is not tied to note values; for instance, a triple meter could involve three half notes, three quarter notes, three eighth notes, three sixteenth notes, or three notes of any duration. Musicians and composers regularly mix duple and triple meter in their work; Igor Stravinsky's "The Rite of Spring" is a textbook example of such a technique. 3. Tempo: Tempo is the speed at which a piece of music is played. There are three primary ways that tempo is communicated to players: beats per minute, Italian terminology, and modern language. Beats per minute (or BPM) indicates the number of beats in one minute. Certain Italian words like largo, andante, allegro, and presto convey tempo change by describing the speed of the music. Finally, some composers indicate tempo with casual English words such as “fast,” “slow,” “lazy,” “relaxed,” and “moderate.” 4. Strong beats and weak beats: Rhythm combines strong beats and weak beats. Strong beats include the first beat of each measure (the downbeat), as well as other heavily accented beats. Both popular music and classical music combine strong beats and weak beats to create memorable rhythmic patterns. 5. Syncopation: Syncopated rhythms are those that do not align with the downbeats of individual measures. A syncopated beat will put its emphasis on traditional weak beats, such as the second eighth note in a measure of 4/4. Complex rhythms tend to include syncopation. While these rhythms may be more difficult for a beginning musician to pick up, they tend to sound more striking than non-syncopated rhythmic patterns. 6. Accents: Accents refer to special emphases on certain beats. To understand accents, think of a piece of poetry. A poetic meter, such as iambic pentameter, may dictate a specific mixture of stressed syllables and unstressed syllables. Musical accents are no different. Different rhythms may share a time signature and tempo, but they stand out from one another by accenting different notes and beats. 7. Polyrhythms: To achieve a particularly ambitious sense of rhythm, an ensemble may employ polyrhythm, which layers one type of rhythm on top of another. For instance, a salsa percussion ensemble may feature congas and bongos playing 4/4 time, while the timbales concurrently play a pattern in 3/8. This creates a dense rhythmic stew and, when properly executed, it can yield incredibly danceable rhythm patterns. Polyrhythms originated in African drumming, and they’ve spread to all sorts of genres worldwide, from Afro-Caribbean to Indian to progressive rock, jazz, and contemporary classical.Key Word Definition
Aid Assistance in the form of grants or loans at below market rates. For example, the UK provided aid to Nepal after the 2015 earthquake to help with reconstruction efforts.
Barriers to Trade Government constraints on the flow of international goods and services, such as tariffs and quotas. For example, the European Union imposes tariffs on certain agricultural products to protect its farmers.
BRICS An acronym for an association of five major emerging nations: Brazil, Russia, India, China, and South Africa. For example, BRICS nations often meet to discuss economic cooperation and development strategies.
Demographic Aging The rise in the median age of a population. For example, Japan is experiencing demographic aging, with a significant increase in the elderly population.
Economic Core Region The most highly developed region(s) in a country. For example, London is considered an economic core region in the UK due to its high level of development and economic activity.
GNP (Gross National Product) GDP plus overseas earnings, also known as GNI (Gross National Income). For example, the GNP of the United States includes the value of goods and services produced domestically and the income earned by its citizens abroad.
HIC (Higher Income Country) A country with a high level of income and development. For example, Germany is classified as a higher income country due to its high GDP per capita and advanced infrastructure.
NEE (Newly Emerging Economy) A country that is experiencing rapid economic growth and industrialisation. For example, China is an example of a newly emerging economy, having rapidly industrialised and grown economically over the past few decades.
LIC (Lower Income Country) A country with a low level of income and development. For example, Malawi is considered a lower income country, with a low GDP per capita and limited access to healthcare and education.
GDHI (Gross Disposable Household Income) The amount of money that households have available for spending and saving after taxes and social contributions. For example, in the UK, the GDHI varies significantly between regions, with London having one of the highest levels.
Gini Coefficient A measure of income inequality within a population, ranging from 0 (perfect equality) to 100 (perfect inequality). For example, South Africa has a high Gini coefficient, indicating significant income inequality within the country.
Trade Unions Organisations that promote trade between member countries, such as the East African Community (EAC). For example, the East African Community (EAC) works to promote economic integration and trade among its member states.
Fair Trade A movement aimed at helping producers in developing countries achieve better trading conditions and promote sustainability. For example, Fairtrade coffee ensures that farmers receive a fair price for their product and work under safe conditions.
FDI (Foreign Direct Investment) Investment made by a company or individual in one country in business interests in another country. For example, Toyota's investment in manufacturing plants in the UK is an example of foreign direct investment.
Debt Relief The partial or total remission of debts, especially those owed by developing countries to external creditors. For example, the Heavily Indebted Poor Countries (HIPC) initiative provides debt relief to eligible countries to help them achieve sustainable development.
International Aid Voluntary transfer of resources from one country to another, often in the form of financial assistance, goods, or services. For example, the UK provides international aid to various countries through its Department for International Development (DFID).
Top-Down Development Large-scale development projects led by national governments or international organisations. For example, the construction of the Three Gorges Dam in China is an example of a top-down development project.
Bottom-Up Development Small-scale development projects led by local communities or NGOs, focusing on the needs of the poorest and most vulnerable. For example, WaterAid's installation of hand pumps in rural villages in Africa is an example of a bottom-up development project.
Urbanisation The increase in the proportion of people living in urban areas compared to rural areas. For example, rapid urbanisation in India has led to the growth of megacities like Mumbai and Delhi.
Geopolitics The study of the effects of geography (human and physical) on international politics and relations. For example, the geopolitics of the Arctic region involves disputes over territorial claims and access to natural resources.
Quality of Life The general well-being of individuals and societies, outlining negative and positive features of life. For example, Scandinavian countries are often ranked high in quality of life due to their strong social welfare systems and high levels of happiness.
Poverty Cycle A set of factors or events by which poverty, once started, is likely to continue unless there is outside intervention. For example, lack of education and healthcare can trap families in a poverty cycle, making it difficult for future generations to improve their living standards.
Sustainable Development Economic development that is conducted without depletion of natural resources. For example, the use of renewable energy sources like wind and solar power is a key aspect of sustainable development.
Humanitarian Aid Material or logistical assistance provided for humanitarian purposes, typically in response to crises including natural disasters and man-made disaster. For example, humanitarian aid was provided to Haiti after the devastating earthquake in 2010 to help with immediate relief efforts.
Economic Growth An increase in the production of goods and services in an economy over a period of time. For example, China's economic growth over the past few decades has lifted millions of people out of poverty.
Social Indicators Measures that describe the well-being of individuals or communities, such as health, education, and income. For example, life expectancy and literacy rates are common social indicators used to assess development.
Environmental Sustainability Responsible interaction with the environment to avoid depletion or degradation of natural resources and allow for long-term environmental quality. For example, practices like recycling and conservation of natural habitats contribute to environmental sustainability.
Infrastructure The basic physical and organisational structures and facilities needed for the operation of a society or enterprise. For example, good infrastructure, such as roads, bridges, and schools, is essential for economic development.
Globalisation The process by which businesses or other organisations develop international influence or start operating on an international scale. For example, the globalisation of technology companies like Apple and Google has led to their products being available worldwide.
Microfinance Financial services provided to low-income individuals or groups who are typically excluded from traditional banking. For example, microfinance institutions like Grameen Bank provide small loans to entrepreneurs in developing countries to help them start or expand their businesses.
Contact with the Americas In 1001, Viking sailors led by Leif Erikson reached the eastern tip of North America. Archaeologists have found evidence of the Viking settlement of Vinland in present-day Newfoundland, Canada. The Vikings did not stay in Vinland long and no one is sure why they left. However, Viking stories describe fierce battles with Skraelings, the Viking name for the Inuit. Evidence suggests that Asians continued to cross the Bering Sea into North America after the last ice age ended. Some scholars believe that ancient seafarers from Polynesia may have traveled to the Americas using their knowledge of the stars and winds. Modern Polynesians have sailed canoes thousands of miles in this way. Still others think that fishing boats from China and Japan blew off course and landed on the western coast of North or South America. Perhaps such voyages occurred. If so, they were long forgotten. Before 1492, the peoples of Asia and Europe had no knowledge of the Americas and their remarkable civilizations. The Voyages of Columbus Portuguese sailors had pioneered new routes around Africa toward Asia in the late 1400s. Spain, too, wanted a share of the riches. King Ferdinand and Queen Isabella hoped to keep their rival, Portugal, from controlling trade with India, China, and Japan. They agreed to finance a voyage of exploration by Christopher Columbus. Columbus, an Italian sea captain, planned to reach the East Indies by sailing west across the Atlantic. Finding a sea route straight to Asia would give the Spanish direct access to the silks, spices, and precious metals of Asia. The spice trade was a major cause for European exploration and a reason the Spanish rulers supported Columbus’s voyage. They also wanted wealth from any source. “Get gold,” King Ferdinand said to Columbus. “Humanely if possible, but at all hazards—get gold.” Crossing the Atlantic In August 1492, Columbus set out with three ships and about 90 sailors. As captain, he commanded the largest vessel, the Santa María. The other ships were the Niña and the Pinta. After a brief stop at the Canary Islands, the little fleet continued west into unknown seas. Fair winds sped them along, but a month passed without the sight of land. Some sailors began to grumble. They had never been away from land for so long and feared being lost at sea. Still, Columbus sailed on. On October 7, sailors saw flocks of birds flying southwest. Columbus changed course to follow the birds. A few days later, crew members spotted tree branches and flowers floating in the water. At 2 a.m. on October 12, the lookout on the Pinta spotted white cliffs shining in the moonlight. “Tierra! Tierra!” he shouted. “Land! Land!” At dawn, Columbus rowed ashore and planted the banner of Spain. He was convinced that he had reached the East Indies in Asia. He called the people he found there “Indians.” In fact, he had reached islands off the coasts of North America and South America in the Caribbean Sea. These islands later became known as the West Indies. For three months, Columbus explored the West Indies. To his delight, he found signs of gold on the islands. Eager to report his success, he returned to Spain. Columbus Claims Lands for Spain In Spain, Columbus presented Queen Isabella and King Ferdinand with gifts of pink pearls and brilliantly colored parrots. Columbus brought with him many things that Europeans had never seen before: tobacco, pineapples, and hammocks used for sleeping. Columbus also described the “Indians” he had met, the Taino (ty noh). The Taino, he promised, could easily be converted to Christianity and could also be used as slaves. The Spanish monarchs were impressed. They gave Columbus the title Admiral of the Ocean Sea. They also agreed to finance future voyages. The promise of great wealth, and the chance to spread Christianity, gave them a reason to explore further. Columbus made three more voyages across the Atlantic. In 1493, he founded the first Spanish colony in the Americas, Santo Domingo, on an island he called Hispaniola (present-day Haiti and the Dominican Republic). A colony is an area settled and ruled by the government of a distant land. Columbus also explored present-day Cuba and Jamaica. He sailed along the coasts of Central America and northern South America. He claimed all of these lands for Queen Isabella of Spain. Columbus proved to be a better explorer than governor. During his third expedition, settlers on Hispaniola complained of his harsh rule. Queen Isabella appointed an investigator, who sent Columbus back to Spain in chains. In the end, the queen pardoned Columbus, but he never regained the honors he had won earlier. He died in 1506, still convinced that he had reached Asia. The Impact of Columbus’s Voyages Columbus has long been honored as the bold sea captain who “discovered America.” Today, we recognize that American Indians had discovered and settled these lands long before 1492. We also recognize that Columbus and the Europeans who followed him treated the ancient inhabitants of the Americas brutally. Still, Columbus’s voyages did change history. They marked the beginning of lasting contact among the peoples of Europe, Africa, and the Americas. For a great many American Indians, contact had tragic results. Columbus and those who followed were convinced that European culture was superior to that of the Indians. The Spanish claimed Taino lands and forced the Taino to work in gold mines, on ranches, or in Spanish households. Many Taino died from harsh conditions or European diseases. The Taino population was wiped out. Still, the voyages of Columbus signaled a turning point for the Americas. A turning point is a moment in history that marks a decisive change. Curious Europeans saw the new lands as a place where they could settle, trade, and grow rich. Spanish Exploration Continues After the voyages of Columbus, the Spanish explored and settled other Caribbean islands that Columbus had found. They sought gold, land for crops, people to enslave, and converts to Christianity for the Spanish crown. By 1511, they had conquered Puerto Rico, Jamaica, and Cuba. They also explored the eastern coasts of North America and South America in search of a western route to Asia. In 1513, Vasco Núñez de Balboa (bal boh uh) crossed the Isthmus of Panama. American Indians had told him that a large body of water lay to the west. With a party of Spanish soldiers and Indians, Balboa reached the Pacific Ocean and claimed the ocean for Spain. The Spanish had no idea how wide the Pacific was until a sea captain named Ferdinand Magellan (muh jel un) sailed across it. The expedition—made up of five ships and about 250 crew members—left Spain in 1519. Fifteen months later, it cut through the stormy southern tip of South America by way of what is now known as the Strait of Magellan and entered the Pacific Ocean. Crossing the vast Pacific, the sailors ran out of food: Primary Source “We remained 3 months and 20 days without taking in provisions or other refreshments and ate only old biscuit reduced to powder, full of grubs and stinking from the dirt which rats had made on it. We drank water that was yellow and stinking.” —Antonio Pigafetta, The Diary of Antonio Pigafetta Magellan himself was killed in a battle with the local people of the Philippine Islands off the coast of Asia. In 1522, only one ship and 18 sailors returned to Spain. They were the first people to circumnavigate, or sail completely around, the world. In doing so, they had found an all-water western route to Asia. Europeans became aware of the true size of the Earth. How Did the Columbian Exchange Affect the Rest of the World? The encounter between the peoples of the Eastern and Western Hemispheres sparked a global exchange of goods and ideas. Because it started with the voyages of Columbus, this transfer is known as the Columbian Exchange. The Columbian Exchange refers to a biological and cultural exchange of animals, plants, human populations, diseases, food, government, technology, the arts, and languages. The exchange went in both directions. Europeans learned much from American Indians. At the same time, Europeans contributed in many ways to the culture of the Americas. This exchange also brought about many modifications, or changes, to the physical environment of the Americas, with both positive and negative results. Changing Environments Europeans introduced domestic animals such as chickens from Europe and Africa. European pigs, cattle, and horses often escaped into the wild and multiplied rapidly. Forests and grasslands were converted to pastures. As horses spread through what would become the United States, Indians learned to ride them and used them to carry heavy loads. Plants from Europe and Africa changed the way American Indians lived. The first bananas came from the Canary Islands. By 1520, one Spaniard reported that banana trees had spread “so greatly that it is marvelous to see the great abundance of them.” Oranges, lemons, and figs were also new to the Americas. In North America, explorers also brought such plants as bluegrass, the daisy, and the dandelion. These plants spread quickly in American soil and modified American grasslands. Tragically, Europeans also brought new diseases, such as smallpox and influenza. American Indians had no resistance to these diseases. Historians estimate that within 75 years, diseases from Europe had killed almost 90 percent of the people in the Caribbean Islands and in Mexico. American Indian Influences on Europe, Africa and Asia American Indians introduced Europeans to valuable food crops such as corn, potatoes, sweet potatoes, beans, tomatoes, manioc, squash, peanuts, pineapples, and blueberries. Today, almost half the world’s food crops come from plants that were first grown in the Americas. Europeans carried the new foods with them as they sailed around the world. Everywhere, people’s diets changed and populations increased. In South Asia, people used American hot peppers and chilies to spice stews. Chinese peasants began growing corn and sweet potatoes. Italians made sauces from tomatoes. People in West Africa grew manioc and corn. European settlers often adopted American Indian skills. In the North, Indians showed Europeans how to use snowshoes and trap beavers and other fur-bearing animals. European explorers learned how to paddle Indian canoes. Some leaders studied American Indian political structures. In the 1700s, Benjamin Franklin admired the Iroquois League and urged American colonists to unite in a similar way. Positive and Negative Consequences Through the Columbian Exchange, Europeans and American Indians modified their environments and gained new resources and skills. At the same time, warfare and disease killed many on both sides. Europeans viewed expansion positively. They gained great wealth, explored trade routes, and spread Christianity. Yet their farming, mining, and diseases took a toll on the physical environment and left many American Indians dead. Despite these negatives, the Columbian Exchange shaped the modern world, including what would become the United States.Tobruk, a small town on the Libyan coast, was central to much of the fighting that took place in the Western Desert during the Second World War. It had originally been developed by the Italians during their colonisation of eastern Libya during the early decades of the 20th century. With a sheltered deep water harbour it became a key naval outpost. It was fortified during the 1930s with both coastal defence batteries and a 50 kilometre-long perimeter of reinforced concrete platoon posts, and other supporting infrastructure such as gun positions, headquarters bunkers, underground supply dumps, and observation towers. When British and Commonwealth forces advanced out of Egypt and into Libya in January 1941, Tobruk was their second objective. The Italian defence perimeter was attacked by the 6th Australian Division on the morning of 22 January and the town fell the next morning. The operation resulted in approximately 27,000 Italian prisoners and the capture of over 200 artillery pieces, but cost 49 Australian lives. The 6th Division's advance pressed on beyond Tobruk and eventually they were withdrawn from Libya to be deployed to Greece.The 9th Australian Division was moved in to Libya in February 1941 to garrison the territory captured by the 6th. By this time, however, German troops had arrived in Libya to reinforce their Italian allies and they launched an offensive that the British Commonwealth forces were ill-disposed to hold back. A retreat towards Egypt commenced. The 9th Division was ordered to fall back upon Tobruk, hold it in order deny its port facilities to the Germans, and delay their advance so as to provide time for defences on the Egyptian frontier to be prepared. Tobruk and the 9th Division were subsequently encircled, beginning what became known as "the siege of Tobruk". Reinforced by the 18th Brigade of the 7th Australian Division and other British and Commonwealth troops, and resupplied by the sea, the 9th Division held Tobruk from April to September 1941. During this period it repelled two major German attacks. In September and October the 9th Division, its condition steadily declining, was relieved by the British 70th Division, which continued to defend Tobruk until the siege was finally lifted by Operation Crusader in December. The defence of Tobruk resulted in 749 Australian deaths, and another 604 became prisoners of war. Tobruk was the scene of further heavy fighting in June 1942 when the fortunes of war again saw a British Commonwealth force seeking to deny the port to the enemy. The Axis forces, however, were in no mood for another siege and launched a massive attack to capture it on 20 June. It remained in their hands until their final retreat from Libya in November 1942.John Hurst Edmondson (1914-1941), soldier, was born on 8 October 1914 at Wagga Wagga, New South Wales, only child of native-born parents Joseph William Edmondson, farmer, and his wife Maude Elizabeth, née Hurst. The family moved to a farm near Liverpool when Jack was a child. Educated at Hurlstone Agricultural High School, he worked with his father and became a champion rifle-shooter. He was a council-member of the Liverpool Agricultural Society and acted as a steward at its shows. Having served (from March 1939) in the 4th Battalion, Militia, he enlisted in the Australian Imperial Force on 20 May 1940 and was posted to the 2nd/17th Battalion. Later that month he was promoted acting corporal (substantive in November). Well built and about 5 ft 9 ins (175 cm) tall, Edmondson settled easily into army life and was known as a quiet but efficient soldier. His battalion embarked for the Middle East in October and trained in Palestine. In March 1941 the 2nd/17th moved with other components of the 9th Division to Libya and reached Marsa Brega before an Axis counter-attack forced them to retreat to Tobruk. The siege of the fortress began on 11 April. Two days later the Germans probed the perimeter, targeting a section of the line west of the El Adem Road near Post R33. This strong-point was garrisoned by the 2nd/17th's No.16 Platoon in which Edmondson was a section leader. The enemy intended to clear the post as a bridgehead for an armoured assault on Tobruk.Under cover of darkness thirty Germans infiltrated the barbed wire defences, bringing machine-guns, mortars and two light field-guns. Lieutenant Austin Mackell, commanding No.16 Platoon, led Edmondson's five-man section in an attempt to repel the intruders. Armed with rifles, fixed bayonets and grenades, the party of seven tried to outflank the Germans, but were spotted by the enemy who turned their machine-guns on them. Unknown to his mates, Edmondson was severely wounded in the neck and stomach. Covering fire from R33 ceased at the pre-arranged time of 11.45 p.m. and Mackell ordered his men to charge. Despite his wounds, Edmondson accounted for several enemy soldiers and saved Mackell's life. When the remaining Germans fled, the Australians returned to their lines. Although Edmondson was treated for his wounds, he died before dawn on 14 April 1941. The Germans' armoured attack that morning was thwarted, partly due to the earlier disruption of their plans. Edmondson was buried in Tobruk war cemetery. He had not married. His Victoria Cross, gazetted on 4 July, was the first awarded to a member of Australia's armed forces in World War II. In April 1960 Mrs Edmondson gave her son's medals to the Australian War Memorial, Canberra, where they are displayed alongside his portrait (1958) by Joshua Smith. At Liverpool a public clock commemorates Edmondson, as do the clubrooms used by the sub-branch of the Returned Services League of Australia.Perhaps my nerves will be more under control when I am by myself. There were no entries in the diary until Friday April 18 when she wrote: Fighting terrific in Greece and North Africa…. I dread the casualty list also the heaviest air raid over London to date. Account …. of heavy fighting and much use of bayonet at Tobruk. Also gives an account of a charge in which a Lieutenant and a Corporal took prominent parts on Easter Sunday night. Of course, no names. When I read it …. I was sure the Corporal was Jack…. It said no casualties but …. I know … that all is not well with Jack. ….. (and) Stuffy ….has not come home yet. On Wednesday April 23 she received a letter from Jack dated March 30 and for the first time he said the conditions were bad. The food short, water one bottle for 48 hours. It worried me terribly so I posted a parcel (of) milk tablets, chocolate milk, biscuits (and) cigarettes.Tuesday April 15 I was feeling afraid of something while I was working and packing the cake (and) had a couple of brandys to (keep going).April 26 Received the following telegram in the mail, the bus man brought it in. “It is with deep regret that I have to inform you that Corporal John Hurst Edmondson was killed in action on the 14th April and desire to convey the profound sympathy of the Ministry for the Army and the Military Board.”Her final entry1. What does the name Mlungisi mean? A. The Helper B. The Fixer C. The Brave One D. The Giver → B 2. What kind of person is Mlungisi? A. Rebellious and lazy B. Always fixing problems and helping others C. A mysterious, quiet boy D. A selfish older cousin → B 3. What does the name Velile mean? A. One Who Builds B. The Beloved One C. He Who Popped Out of Nowhere D. He Who Carries Others → C 4. How does Velile behave according to Trevor? A. He is very responsible and hardworking B. He often vanishes and suddenly reappears C. He is a caring father figure D. He is always around to help the family → B 5. Patricia’s name means: A. She Who Gives Back B. She Who Demands More C. The Fighter D. The Lost One → A 6. What did Patricia do as a child in Soweto? A. She went to school and stayed away from others B. She took care of abandoned children and fed them C. She ran away from home frequently D. She helped her father manage a shop → B 7. Where did Patricia find the money to buy food for the children? A. From her allowance B. From selling her toys C. From collecting bottles from shebeens D. From stealing it → C 8. What is a shebeen in this context? A. A school for orphans B. A place for young kids to play C. An informal bar where men would drink D. A shelter for street children → C 9. How old was Patricia when she started helping other children? A. 4 or 5 B. 6 or 7 C. 10 or 11 D. Teenager → B 10. Why did Trevor’s mother choose the name “Trevor”? A. It was the name of her favorite Bible character B. It was her father’s name C. It had no meaning, and she wanted him to be free D. It was a popular name in her family → C 11. What does it mean that Trevor's name had “no precedent” in South Africa? A. It was illegal to use B. It had no cultural or family history C. It came from ancient African myths D. It was a translation of a Zulu name → B 12. What is the deeper reason behind Patricia giving Trevor a name with no meaning? A. She didn’t like traditional names B. She didn’t know what the name meant C. She wanted him to escape fate and create his own identity D. She thought names were unimportant → C 13. According to Trevor, what kind of effect do traditional Xhosa names usually have? A. They are just for decoration B. They are often meaningless C. They tend to become self-fulfilling D. They reflect colonial history → C 14. What literary device is mainly used in the idea of names becoming destiny? A. Hyperbole B. Irony C. Symbolism D. Pun → C 15. Trevor’s mother wanted him to be: A. Bound to cultural tradition B. Free to be anyone he wanted C. A preacher D. Another fixer like Mlungisi → B ★ True or False Questions (判断题)（共10题） 16. Trevor’s cousin Mlungisi was known for always creating trouble. → False 17. Velile’s name and personality are both connected to sudden appearances and disappearances. → True 18. Patricia started caring for others when she was already an adult. → False 19. Shebeens were places where children gathered to play and eat. → False 20. Patricia used money she earned at a job to feed other children. → False （她用换瓶子的钱） 21. Trevor’s name has no Biblical or cultural background. → True 22. Patricia believed that names could shape a person’s life. → True 23. Trevor’s mother gave him a name with no meaning because she didn’t care about names. → False 24. Xhosa names often carry strong cultural or symbolic meanings. → True 25. Trevor’s mother gave him a name with no meaning so that he could be free from expectations. → TrueDemocratic Constitution in South Africa Struggle against Apartheid • Apartheid was the name of a system of racial discrimination unique to South Africa. • This system was particularly oppressive for the blacks. → They were forbidden from living in white areas. • Since 1950, the blacks, coloured and Indians fought against the apartheid system. • The African National Congress (ANC) was the umbrella organisation that led the struggle against the policies of segregation. • In 1964, Nelson Mandela and seven other leaders were sentenced to life imprisonment in 1964 for daring to oppose the apartheid regime in his country. Towards a New Constitution • As protests and struggles against apartheid had increased, the white regime changed its policies. • After 28 years of imprisonment, Nelson Mandela released from jail. • At the midnight of 26 April 1994, democracy was adopted as a form of government in South Africa. • After two years, a constitution came out which gave to its citizens the most extensive rights available in any country. Why do we need a Constitution? • A constitution is necessary because: → It generates a degree of trust and coordination that is necessary for different kind of people to live together. → It specifies how the government will be constituted, who will have power to take which decisions. → It lays down limits on the powers of the government and tells us what the rights of the citizens are. → It expresses the aspirations of the people about creating a good society. Making of the Indian Constitution • In 1928, Motilal Nehru and eight other Congress leaders drafted a constitution for India. • In 1931, the resolution at the Karachi session of the Indian National Congress dwelt on how independent India’s constitution should look like. • Factors contributed to the making of our Constitution. → Ideals of French Revolution → The practice of parliamentary democracy in Britain → The Bill of Rights in the US → The socialist revolution in Russia The Constituent Assembly • In July 1946, Elections to the Constituent Assembly were held. → The drafting of the document called the constitution was done Constituent Assembly. → Dr. Rajendra Prasad was the Chairman of the Constituent Assembly. → In December 1946, the first meeting was held. • After the country was divided into India and Pakistan, the Constituent Assembly also got divided. • The Assembly adopted the Constitution on 26 November 1949 but it came into effect on 26 January 1950. • To mark this day we celebrate January 26 as Republic Day every year. • The Constituent Assembly worked in a systematic, open and consensual manner. → First some basic principles were decided and agreed upon. → Then a Drafting Committee chaired by Dr. B.R. Ambedkar prepared a draft constitution for discussion. → More than two thousand amendments were considered. Philosophy of the Constitution • The Constitution begins with a short statement of its basic values which is called the Preamble to the constitution. The preamble focuses on: → Justice, social, economic and political. → Liberty of thoughts, expression, belief, faith and worship. → Equality of status and of opportunity. → Fraternity assuring the dignity of the individual and the unity and integrity of the nation.Figure 18-11 represents the amount of energy stored as organic material in each trophic level in an ecosystem. The pyramid shape of the diagram indicates the low percentage of energy transfer from one level to the next. On average, 10 percent of the total energy consumed in one trophic level is incor- porated into the organisms in the next. Why is the percentage of energy transfer so low? One reason is that some of the organisms in a trophic level escape being eaten. They eventually die and become food for decomposers, but the energy contained in their bodies does not pass to a higher trophic level. Even when an organism is eaten, some of the molecules in its body will be in a form that the consumer cannot break down and use. For example, a cougar cannot extract energy from the antlers, hooves, and hair of a deer. Also, the energy used by prey for cellu- lar respiration cannot be used by predators to synthesize new bio- mass. Finally, no transformation or transfer of energy is 100 percent efficient. Every time energy is transformed, such as during the reactions of metabolism, some energy is lost as heat. Limitations of Trophic Levels The low rate of energy transfer between trophic levels explains why ecosystems rarely contain more than a few trophic levels. Because only about 10 percent of the energy available at one trophic level is transferred to the next trophic level, there is not enough energy in the top trophic level to support more levels. Organisms at the lowest trophic level are usually much more abundant than organisms at the highest level. In Africa, for exam- ple, you will see about 1,000 zebras, gazelles, and other herbivores for every lion or leopard you see, and there are far more grasses and shrubs than there are herbivores. Higher trophic levels con- tain less energy, so, they can support fewer individuals.A population is a group of organisms that belong to the same species and live in a particular place at the same time. All of the bass living in a pond during a certain period of time make up a pop- ulation because they are isolated in the pond and do not interact with bass living in other ponds. The boundaries of a population may be imposed by a feature of the environment, such as a lake shore, or they can be arbitrarily chosen to simplify a study of the population. The humans shown in Figure 19-1 are part of the pop- ulation of a city. The properties of populations differ from those of individuals. An individual may be born, it may reproduce, or it may die. A population study focuses on a population as a whole—how many individuals are born, how many die, and so on. Population Size A population’s size is the number of individuals that the population contains. Size is a fundamental and important population property but can be difficult to measure directly. If a population is small and composed of immobile organisms, such as plants, its size can be determined simply by counting individuals. Often, though, individ- uals are too abundant, too widespread, or too mobile to be counted easily, and scientists must estimate the number of individuals in the population. Suppose that a scientist wants to know how many oak trees live in a 10 km2 patch of forest. Instead of searching the entire patch of forest and counting all the oak trees, the scientist could count the trees in a smaller section of the forest, such as a 1 km2 area. The scientist could then use this value to estimate the population of the larger area. SECTION 1 OBJECTIVES ● Describe the main properties that scientists measure when they study populations. ● Compare the three general patterns of population dispersion. ● Identify the measurements used to describe changing populations. ● Compare the three general types of survivorship curves. VOCABULARY population population density dispersion birth rate death rate life expectancy age structure survivorship curve FIGURE 19-1 A population can be widely distributed, as Earth’s human population is, or confined to a small area, as species of fish in a lake are. Copyright © by Holt, Rinehart and Winston. All rights reserved. 382 CHAPTER 19 If the small patch contains 25 oaks, an area 10 times larger would likely contain 10 times as many oak trees. A similar kind of sampling technique might be used to estimate the size of the pop- ulation shown in Figure 19-2. To use this kind of estimate, the sci- entist must assume that the distribution of individuals in the entire population is the same as that in the sampled group. Estimates of population size are based on many such assumptions, so all esti- mates have the potential for error. Population Density Population density measures how crowded a population is. This measurement is always expressed as the number of individuals per unit of area or volume. For example, the population density of humans in the United States is about 30 people per square kilome- ter. Table 19-1 shows the population sizes and densities of humans in several countries in 2003. These estimates are calculated for the total land area. Some areas of a country may be sparsely popu- lated, while other areas are very densely populated. Dispersion A third population property is dispersion (di-SPUHR-zhuhn). Dispersion is the spatial distribution of individuals within the popu- lation. In a clumped distribution, individuals are clustered together. In a uniform distribution, individuals are separated by a fairly con- sistent distance. In a random distribution, each individual’s location is independent of the locations of other individuals in the popula- tion. Figure 19-3 illustrates the three possible patterns of dispersion. Clumped distributions often occur when resources such as food or living space are clumped. Clumped distributions may also occur because of a species’ social behavior, such as when animals gather into herds or flocks. Uniform distributions may result from social behavior in which individuals within the same habitat stay as far away from each other as possible. For example, a bird may locate its nest so as to maximize the distance from the nests of other birds. These migrating wildebeests in East Africa are too numerous and mobile to be counted. Scientists must use sampling methods at several locations to monitor changes in the population size of the animals. FIGURE 19-2 TABLE 19-1 Population Size and Density of Some Countries Population size Population density Country (in millions) (in individuals/km2) China 1,289 135 India 1,069 325 United States 292 30 Russia 146 8 Japan 128 337 Mexico 105 54 Kenya 32 54 Australia 20 3 dispersion from the Latin dis-, meaning “out,” and spargere, meaning “to scatter” Word Roots and Origins Copyright © by Holt, Rinehart and Winston. All rights reserved. POPULATIONS 383 The social interactions of birds called gannets, which are shown in Figure 19-3b, result in a uniform distribution. Each gannet chooses a small nesting area on the coast and defends it from other gannets. In this way, each gannet tries to maximize its distance from all of its neighbors, which causes a uniform distribution of individuals. Few populations are truly randomly dispersed. Rather, they show degrees of clumping or uniformity. The dispersion pattern of a population sometimes depends on the scale at which the popu- lation is observed. The gannets shown in Figure 19-3b are uni- formly distributed on a scale of a few meters. However, if the entire island on which the gannets live is observed, the distribution appears clumped because the birds live only near the shore. POPULATION DYNAMICS All populations are dynamic—they change in size and composition over time. To understand these changes, scientists must know more than the population’s size, density, and dispersion. One important measure is the birth rate, the number of births occur- ring in a period of time. In the United States, for example, there are about 4 million births per year. A second important measure is the death rate, or mortality rate, which is the number of deaths in a