EARTH AND SPACE SYSTEMS

Ect weather data. Trackingthe The forecasters have a lot of help! Meteorologists, or scientists who study weather, collect data from all over the world. They use automated systems at sea, on land, in the air, and in space to help track the weather. At sea, weather buoys collect data on coastal weather conditions. These data help keep people in coastal cities safe. On land, weather-monitoring stations track weather conditions in remote locations. They can send advance notice about incoming weather. Scientists also use Doppler radar towers to observe how storm clouds are moving. Weather balloons and weather satellites collect data from high above Earth’s surface. Weather satellites can track the weather over very large areas. They also help relay data from land-based tools to meteorologists around the world. Scientists launch weather balloons that carry tools, called radiosondes, into the atmosphere. A typical radiosonde measures air temperature, air pressure, and humidity. Weather satellites orbit Earth. They collect weather data, such as cloud cover, and track storms, such as hurricanes. These satellites use radio signals to transmit data back to Earth. Packets of air move across Earth’s surface. An air mass is a large body of air with the same temperature and humidity throughout. An air mass reflects the conditions of the place where it forms. Air masses that form over land are dry. Air masses that form over water are moist. Cold air masses form near the poles, and warm air masses form near the tropics. As air masses move across an area, they can collide. The boundary between two air masses is called a front. Weather changes take place at fronts. For example, as a warm front passes over an area, warm air replaces cooler air and the temperature rises. The movement of air masses and fronts explains why you might be chilly one day and warm the next. At a front, stormy conditions are common. Air masses may form over land or water. The masses that form over land near the poles will be cold and dry. The masses that form over water near the poles will be cold and moist. Which types of air masses will form near the tropics? A cold front forms where a cold air mass bumps into a warmer air mass. The denser cold air pushes the warm air up. Water vapor in the air cools, and large clouds form. Thunderstorms and heavy rain often take place. Cooler temperatures follow a cold front. A warm front forms where a warm air mass moves over a cold air mass. A warm front forms a wider area of clouds and rain than a cold front. Steady rain or snow may fall. Warmer temperatures follow a warm front.

THE SOAR SYSTEM A solar system is a group of planets and other celestial bodies that revolve around a star. A solar nebula- a vast cloud of gas and dust, mostly hydrogen and helium. How the Solar System Form • COLLAPSE AND SPINNING DISK FORMATION - Gravity pulls material inward. The cloud flattens into a spinning disk due to conservation of angular momentum. • PROTOSTAR FORMATION- (BIRTH OF THE SUN). Material collects at the center, and begun to heat up. When it reaches to 10 million KELVIN, nuclear fusion begins. thus, SUN is born. • PLANETESIMALS AND PROTOPLANETS. Dust and gas in the disk stick together via static and gravitational forces. These form planetesimals, which grow into protoplanets collision and accretion. • PLANET FORMATION. Inner disk: too hot for gas rocky planets form Mercury, Venus, Earth, Mars. • PLANET FORMATION. Outer disk: gas and ice giants. Jupiter, Saturn, Uranus, Neptune • LEFTOVER DEBRIS. Remaining materials forms moon, asteroids, comets and dwarf planets. DIFFERENT HYPOTHESIS IN THE FORMATION OF SOLAR SYSTEM. 1. NEBULAR HYPOTHESIS- The Solar system formed from a rotating cloud of Gas and Dust (solar nebula). As it rotates conservation of angular momentum caused the cloud to flatten into a disk. the Sun formed at the center (DISK) while planets formed from the surrounding materials through acceleration. thus, it explains the coplanar and nearly circular orbit of the planets all planets orbits around the sun on the same flat, disk shaped plane. Proposed by Immanuel Kant in 1755 and Modified by Pierre Simon Laplace in 1756. PROTOPLANET HYPOTHESIS. The Solar system formed from a rotating cloud of Gas and Dust (solar nebula). As it rotates conservation of angular momentum caused the cloud to flatten into a disk. 2. Protoplanet hypothesis. Builds on the nebular model but focuses more on the role of planetesimals which then form into full planets. PROCESS: - Small solid particles stick together through collisions. As collisions takes place, it grows into kilometer-sized planetesimals. Gravitational interactions lead to the formation of planets. Lead to formation of steroids belts and varying planet sizes 3. Encounter hypothesis. States that the sun encountered a rogue star. The encounter led to the removal of hot gas from both stars due to their gravitational interaction. The hot gas then accumulated and formed the planets. The materials from the less dense rogue star formed the other planets, while that from the sun formed the inner planets. 4. TIDAL HYPOTHESIS. (also called the Tidal Theory) is an early scientific idea about how the solar system might have formed. Proposed by James Jeans and Harold Jeffreys. A massive star passed very close to the early Sun. The hot gas then accumulated and formed the planets. The materials from the less dense rogue star formed the other planets, while that from the sun formed the inner planets. Streams of hot gas were drawn out from the Sun in elongated shape. These streams eventually condensed and cooled, forming planets, moons, and other bodies in the solar system. 5. Not accepted theory. Later studies showed the streams of hot gas would disperse too quickly into space instead of condensing into planets. The theory also couldn’t explain the specific orbital patterns and compositions we see today. Modern science favors the Nebular Hypothesis, which explains solar system formation through the collapse of a rotating gas cloud. Earth as the only habitable planet 1. Right Distance from the Sun (The Goldilocks Zone). Not too hot, not too cold — just right for liquid water to exist. 2. Atmosphere with Oxygen. Earth has a mix of gases, especially oxygen, which most living things need to survive. 3. Liquid Water. Earth has oceans, rivers, and rain — water is essential for all life. 4. Magnetic Field. Earth’s magnetic field protects us from harmful solar radiation. 5. Stable Climate. The atmosphere and natural cycles keep temperatures and weather mostly stable over time. 6. Rich Resources. Earth has soil for growing food, minerals, and energy sources that support life and technology. Solar explorations 1. AUGUST 6, 2014. First space craft to orbit a comet (ROSETTA PROBE). Captures the comet photograph. -Comets have coma and tail as it approaches to the sun. 2. JULY 14, 2015. NASA’s New Horizons spacecraft made history by becoming the first spacecraft to fly by Pluto, giving us our first close-up look at the dwarf planet. First time visiting Pluto. Before this, Pluto was just a blurry dot in telescope images. Revealed a surprising world New Horizons showed mountains of ice, smooth plains, and a heart-shaped region called Tombaugh Regio. Changed what we knew. Scientists thought Pluto would be dull and frozen — instead, it turned out to be geologically active and incredibly complex. 3. SEPTEMBER 8, 2016. NASA launched OSIRIS-REx, the first U.S. mission to collect a sample from an asteroid and return it to Earth. Changed what we knew. Scientists thought Pluto would be dull and frozen — instead, it turned out to be geologically active and incredibly complex. OSIRIS-REx stands for: Origins, Spectral Interpretation, Resource Identification, Security–Regolith Explorer It was sent to study the asteroid Bennu, a near-Earth asteroid about 500 meters wide. Mission Goals: Collect a sample of surface material from Bennu Study the asteroid’s omposition, structure, and history. Mission Goals: Help scientists understand the origins of the solar system. Learn more about asteroids that could impact Earth. 4. August 12, 2018: Launch of NASA’s Parker Solar Probe, the first spacecraft to "touch" the Sun by flying through its outer atmosphere, called the corona. Mission Goal: To study the Sun up close and help scientists understand: How the solar wind (a stream of charged particles) is formed. Why the Sun’s corona is hotter than its surface. What causes solar storms that can affect Earth’s satellites and power grids. 5. November 26, 2018: NASA’s Insight Lander Touches Down on Mars. Its mission was focused on studying the interior of the Red Planet (crust, mantle, and core of the planet). Why the Sun’s corona is hotter than its surface. What causes solar storms that can affect Earth’s satellites and power grids 6. November 26, 2018: NASA’s Insight Lander Touches Down on Mars. Its mission was focused on studying the interior of the Red Planet (crust, mantle, and core of the planet) 7. JULY 30, 2020 PERSEVERANCE PROBE. Perseverance rover as part of the Mars 2020 mission aboard an Atlas V-541 rocket This marked a major step in Mars exploration. 8. DECEMBER 25, 2021-JAMES WEBB SPACE TELESCOPE. Investigate exoplanets’ atmospheres for signs of habitability. Observe the first galaxies formed after the Big Bang. Study the formation of stars and planetary systems. Look deeper into the infrared universe than ever before. RESULTS OF EXPLORATION • Evidence of Ancient Life-friendly Environment. • Sedimentary rocks formed in water-rich environments. • Signs of clay and carbonate minerals, which can preserve biosignatures (traces of past life). • Evidence of Ancient Life-friendly Environment. • Sedimentary rocks formed in water-rich environments. • Signs of clay and carbonate minerals, which can preserve biosignatures (traces of past life). • Evidence of Ancient Life-friendly Environment. • Sedimentary rocks formed in water-rich environments. • Signs of clay and carbonate minerals, which can preserve biosignatures (traces of past life).

Why should mankind explore space? Why should money, time and effort be spent exploring, investigating and researching something with so few apparent benefits? Why should resources be spent on space rather than on conditions and people on Earth? These are questions that, understandably, are very often asked. Perhaps the best answer lies in our genetic makeup as human beings. What drove our distant ancestors to move from the trees into the plains, and on into all possible areas and environments? It appears that we are driven to ensure the success and continuation of not just our own genes, but of the species as a whole. The wider the distribution of a species, the better its chance of survival. Perhaps the best reason for exploring space is this genetic predisposition to expand wherever possible. Nearly every successful civilisation has explored, because by doing so, any dangers in surrounding areas can be identified and prepared for. These might be enemies in neighbouring cultures, physical features of the area, a change in the area which might affect food supplies, or any number of other factors. They all pose a real danger, and all can be made less threatening if certain preparations are made. Without knowledge, we may be completely destroyed by the danger. With knowledge, we can lessen its effects. Exploration also allows minerals and other potential resources to be located. Additional resources are always beneficial when used wisely, and can increase our chances of survival. Even if we have no immediate need of them, they will perhaps be useful later. Resources may be more than physical assets. Knowledge or techniques acquired through exploration, or preparing to explore, filter from the developers into society at large. The techniques may have medical applications which can improve the length or quality of our lives. Techniques may be social, allowing members of society better to understand those within or outside the culture. Better understanding may lead to more efficient use of resources, or a reduction in competition for resources. We have already benefited from other spin-offs, including improvements in earthquake prediction – which has saved many lives – in satellites used for weather forecasting and in communications systems. Even non-stick saucepans and mirrored sunglasses are by-products of technological developments in the space industry! While many resources are spent on what seems a small return, the exploration of space allows creative, brave and intelligent members of our species to focus on what may serve to save us. While space may hold many wonders and explanations of how the universe was formed or how it works, it also holds dangers. The chances of a large comet or asteroid hitting the Earth are small, but it could happen in time. Such strikes in the past may account for the extinction of dinosaurs and other species. Human technology is reaching the point where it might be able to detect the possibility of this happening, and enable us to minimise the damage, or prevent it completely, allowing us as a species to avoid extinction. The danger exists, but knowledge can help human beings to survive. Without the ability to reach out across space, the chance to save ourselves might not exist. In certain circumstances, life on Earth may become impossible: over-population or epidemics, for instance, might eventually force us to find other places to live. While Earth is the only planet known to sustain life, surely the adaptive ability of humans would allow us to inhabit other planets and moons. It is true that the lifestyle would be different, but human life and cultures have adapted in the past and surely could in the future. The more a culture expands, the less chance there is that it will become extinct. Space allows us to expand and succeed: for the sake of everyone on the Earth, now and in the future, space exploration is essential.

Earth and Space Planets of Our Solar System

Alright, Isti — here’s a longer and more detailed English version of the Isaac Newton text, still written at a level that’s accessible for Grade 4 students, but rich enough in information to meet PISA literacy expectations and EF A2-level vocabulary. I’ve kept sentences short, clear, and with explanations for new concepts so it’s easier for young learners to follow, while still including both famous facts and lesser-known stories. ⸻ Isaac Newton: The Man Who Changed the Way We See the World A Boy from a Small Village Isaac Newton was born on January 4, 1643, in Woolsthorpe, a small village in England. His life was not easy. His father died before he was born. When he was just a few months old, his mother remarried and left him to live with his grandmother. Isaac missed his parents, but he kept himself busy by making things and exploring the world around him. As a child, Isaac liked to build models and machines. He made a small windmill that could turn with the wind. He built a water clock that told the time by dripping water into a container. He even made a sundial — a clock that tells the time by using the shadow of the sun. 💡 Did you know? The sundial marks that Isaac carved as a boy can still be seen today on the wall of his old house. ⸻ School and Curiosity When Newton first went to school, he was not the top student. At first, he did not pay much attention in class. But one day, another boy teased him for not being smart. Newton decided to study hard to prove him wrong. Soon, he became the best in his class. Isaac loved asking questions. He wanted to know how and why things happened. He enjoyed watching the stars at night and thinking about how the world worked. ⸻ The Falling Apple and Gravity One of the most famous stories about Newton is the falling apple. One afternoon, Isaac sat in his mother’s garden and saw an apple drop from a tree. This made him think: “Why does the apple fall straight down? Why doesn’t it fly up into the sky?” From this question, Newton began to think about gravity — an invisible force that pulls objects toward each other. Gravity is what keeps our feet on the ground. It’s also what keeps the Moon moving around the Earth and the planets moving around the Sun. 💡 Fun fact: The apple did not hit Newton’s head. That’s just a story people made up later to make the tale more exciting. ⸻ Newton’s Three Laws of Motion Newton studied movement and wrote three important rules: 1. Objects stay still or keep moving unless something makes them change. • Example: A ball will not roll unless you push it. 2. The bigger the push, the bigger the movement. • Example: If you kick a ball harder, it will go faster and farther. 3. Every action has an equal and opposite reaction. • Example: When you jump off a boat, the boat moves backward as you move forward. These three laws are still used today to understand how cars, rockets, and even roller coasters work. ⸻ Discoveries in Light and Color Newton also studied light. He found that white light is not just one color — it is made of many colors. He used a glass prism to split sunlight into a rainbow. This helped scientists understand how colors work. ⸻ Inventions and New Ideas Newton made a special telescope that used mirrors instead of lenses. This type of telescope made images of planets and stars much clearer. It is still called the Newtonian telescope today. He also worked in mathematics and helped create a new type of math called calculus, which is used to study changes and movement. ⸻ Strange Experiments Newton was so curious that he sometimes tested ideas on himself. Once, he put a thin needle, called a bodkin, beside his eye to see how it would change his vision. It was very dangerous, but luckily he did not go blind. 💡 Did you know? Newton also studied alchemy — an old kind of science where people tried to turn metal into gold. He never succeeded, but it showed how wide his interests were. ⸻ Later Life and Work At the age of 27, Newton became a professor at Cambridge University. He later worked for the Royal Mint, making sure coins were made safely and stopping people from making fake money. He was very strict, and some criminals were sent to prison because of his work. Newton never married. He spent most of his life reading, writing, and doing experiments. ⸻ The End of His Life Isaac Newton died in 1727 at the age of 84. He was buried in Westminster Abbey, a famous place in London where great people of Britain are honored. His work changed the world forever. Even today, scientists, engineers, and students still use Newton’s laws and ideas. 💬 Newton once said: “If I have seen further, it is by standing on the shoulders of giants.” This means we can make new discoveries by learning from the work of others who came before us. give 10 questions to each passage with PISA literacy standard for kid 10 years, 1. Nikola Tesla: The Man Who Dreamed of Lightning Born: July 10, 1856 Died: January 7, 1943 When Nikola Tesla was a boy in Croatia, he saw a flash of lightning and asked his mother, “Can we catch the light?” That question never left him. As he grew older, Tesla became a brilliant inventor, especially fascinated by electricity. He believed in a future where energy could be sent wirelessly through the air—like music through the radio! Tesla invented the alternating current (AC) system, which became the foundation of modern electricity. At the time, Thomas Edison promoted direct current (DC), and the two men had a fierce competition. Many laughed at Tesla's bold ideas, but he never gave up. He dreamed of wireless communication, flying machines, and even free energy for everyone. Though he died alone and poor, today the world honors his vision. Think About It: Why do you think people didn’t believe Tesla at first? What can we learn from Tesla’s courage to dream big? 2. Charles Darwin: The Man Who Studied the World’s Weirdest Creatures Born: February 12, 1809 Died: April 19, 1882 When young Charles Darwin got on a ship called HMS Beagle, he didn’t know he would change science forever. He sailed around the world for five years, collecting plants, animals, and fossils. On the Galápagos Islands, he noticed something curious: finches had different beaks depending on their island. Why? Darwin’s observations led him to write the theory of evolution by natural selection. It explained how animals adapt and survive. But his ideas shocked many people because they seemed to challenge religious beliefs. Despite the controversy, Darwin continued his work. His book On the Origin of Species changed how we see life on Earth. Think About It: Should scientists share their ideas even if they go against what others believe? How did traveling help Darwin make new discoveries? 3. Marie Curie: The Woman Who Glowed in the Dark Born: November 7, 1867 Died: July 4, 1934 Marie Curie was born in Poland at a time when girls were not allowed to study science. But that didn’t stop her. She moved to France, worked day and night, and discovered radioactivity, a powerful energy hidden inside atoms. She and her husband, Pierre Curie, found two new elements: polonium and radium. She became the first woman to win a Nobel Prize, and the only person to win in two different sciences: physics and chemistry. Even when Pierre died in an accident, Marie continued their work. Her discoveries helped doctors treat cancer—but working with radioactive materials also harmed her health. She died from radiation exposure, but her legacy lives on. Think About It: What challenges did Marie Curie face as a woman in science? Why is it important to balance discovery with safety? 4. Galileo Galilei: The Star Watcher Who Defied the Church Born: February 15, 1564 Died: January 8, 1642 Galileo loved looking at the stars. He built one of the first powerful telescopes and made stunning discoveries: mountains on the Moon, moons around Jupiter, and that the Earth orbits the Sun—not the other way around. This idea, called heliocentrism, went against the teachings of the Church. He was put on trial and forced to say he was wrong. But he wasn’t. He spent his last years under house arrest, quietly writing. Today, Galileo is called the father of modern science for daring to question what others blindly believed. Think About It: Why do you think Galileo was punished for telling the truth? Should science always follow evidence, even if it goes against powerful beliefs? 5. Isaac Newton: The Man Who Asked “Why?” When an Apple Fell Born: January 4, 1643 Died: March 31, 1727 One day, an apple fell from a tree, and Isaac Newton began to wonder: Why did it fall down, not sideways or up? This simple question led to his theory of gravity. Newton also invented calculus, described the laws of motion, and changed physics forever. But Newton wasn’t just a genius—he was curious, quiet, and often worked alone. He believed everything in nature followed rules, and it was our job to discover them. Thanks to him, we understand how planets move, how rockets launch, and why you fall when you trip. Think About It: How did Newton’s curiosity lead to great discoveries? Do you think working alone helped or hurt Newton? 6. Ada Lovelace: The First Computer Programmer Before Computers Existed Born: December 10, 1815 Died: November 27, 1852 Ada Lovelace was the daughter of the famous poet Lord Byron, but she didn’t love poetry—she loved numbers! At a time when girls were expected to sew, Ada studied mathematics. She met Charles Babbage, who designed an early computer called the Analytical Engine. Ada imagined the machine could do more than just math—it could create music, art, and even write! She wrote what is now considered the first computer program, long before real computers were built. Think About It: How did Ada imagine something that didn’t exist yet? Why do we call her a pioneer in technology? 7. Albert Einstein: The Man Who Brought Time and Space Together Born: March 14, 1879 Died: April 18, 1955 Albert Einstein wasn’t always a good student. In fact, his teachers thought he was slow. But Einstein thought deeply. He asked big questions like, “What if you could ride a beam of light?” His theories of relativity changed how we see space, time, and gravity. He also warned the world about the dangers of nuclear weapons, even though his ideas helped create them. Einstein believed science should help people, not harm them. With his messy hair, kind smile, and brilliant mind, he remains a symbol of genius. Think About It: Can someone be bad in school but still be brilliant? Should scientists be responsible for how their inventions are used? 8. Pythagoras: The Musician Who Loved Math Born: Around 570 BC Died: Around 495 BC Long ago in ancient Greece, Pythagoras believed the universe followed numbers. He discovered the Pythagorean Theorem, a rule about triangles that helps us build houses, design computers, and navigate space. He also believed that music had math inside it—that certain notes made perfect harmony because of mathematical ratios. Pythagoras started a secret school and taught his students to search for truth through numbers, shapes, and sound. Think About It: Why do you think Pythagoras saw math in everything? How does music relate to math? 9. Rosalind Franklin: The Woman Behind the DNA Discovery Born: July 25, 1920 Died: April 16, 1958 Rosalind Franklin loved looking closely at things. She used a special machine called X-ray crystallography to photograph molecules. One of her greatest photos, called Photo 51, showed the shape of DNA, the molecule that carries life’s instructions. But her work was taken without credit. Two men, Watson and Crick, used her photo to build their famous model of DNA and won the Nobel Prize. Rosalind died young and never knew how important her work became. Think About It: Why is it important to give credit in science? What can we learn from Rosalind’s quiet strength? 10. Carl Linnaeus: The Man Who Gave Names to Everything Born: May 23, 1707 Died: January 10, 1778 Have you ever wondered why a tiger is called Panthera tigris? That’s thanks to Carl Linnaeus, a Swedish scientist who created a way to name and organize every living thing. His system is still used today in biology. Linnaeus loved nature and spent his life collecting plants, animals, and even rocks. He believed that by organizing life, we could better understand it. Thanks to him, we now have a global “dictionary of nature.” Think About It: Why is it important to name and organize living things? How does order help us understand the world?

meteor meteorite meteoroid Milky Way moon Neptune orbit physical characteristics Pluto revolve / revolution rotate / rotation Saturn solar system Sun Uranus Venus Essential Understandings (Content Elaboration): ● Planets in the solar system orbit the sun. Some of the planets have one or more orbiting moons. Earth is a planet that has a moon. The moon orbits Earth. Gravitational forces between the sun and its planets cause the planets to orbit the sun. Gravitational forces between a planet and its moon(s) cause the moon(s) to orbit the planet. If no forces were present, planets and moons would continue their motion toward outer space without changes in speed or direction. However, gravitational forces between the sun and each planet continuously change the planet’s direction so it remains in orbit. In the same way, gravitational forces between each moon and its planet continuously change the moon’s direction so it remains in orbit.

hysical features of Southeast Asia The physiography of Southeast Asia has been formed to a large extent by the convergence of three of the Earth’s major crustal units: the Eurasian, Indian-Australian, and Pacific plates. The land has been subjected to a considerable amount of faulting, folding, uplifting, and volcanic activity over geologic time, and much of the region is mountainous. There are marked structural differences between the mainland and insular portions of the region. Mainland Southeast Asia The mainland is characterized by a series of generally north–south-trending mountain ranges separated by a number of major river valleys and their associated deltas. In many ways these ranges resemble ribs in a fan, where the interstices are deep trenches carved by the rivers. Although the mainland as a whole is similar in a structural sense, its various geologic components and the time periods of their orogenic (mountain-building) episodes differ. Much of the region has been affected by the gradual, continuing collision of the Indian subcontinent with the Eurasian Plate over roughly the past 50 million years, an event that—with diminishing intensity from west to east—has been responsible for deforming the land. Nonetheless, mainland Southeast Asia is relatively stable geologically, with no active or recently active volcanoes and, except in the northwest and north, little seismic activity. The ranges fan out southward from the southeastern corner of the Plateau of Tibet, where they are tightly spaced. A major rib of this system extends through the entire western margin of Myanmar (Burma); describing an elongated letter S, it consists of (from north to south) the Pātkai Range, Nāga Hills, Chin Hills, and Arakan Mountains. Farther to the south the same rib emerges from beneath the sea to become the Andaman and Nicobar Islands of India. Another major system extends along a straight north-south axis from eastern Myanmar east of the Salween River through northwestern Thailand to south of the Isthmus of Kra on the Malay Peninsula. It consists of a series of elongated blocks rather than one continuous ridge. The core of these blocks is granite, which has intruded into previously folded and faulted limestone and sandstone. The altitudes of the ranges diminish from above 8,000 feet (2,440 meters) on the Chinese border in the north to below 4,000 feet on the Isthmus of Kra, and the ranges are spread farther apart toward the south. The easternmost major mountain feature on the mainland is the Annamese Cordillera (Chaîne Annamitique) in Laos and Vietnam. In the portion between Laos and Vietnam, the chain forms a nearly straight spine of ranges from northwest to southeast, with a steep face rising from the South China Sea to the east and a more gradual slope to the west. The mountains thin out considerably south of Laos and become asymmetrical in form. The upland zone is characterized by a number of plateau remnants. The rather neat fanlike pattern of the mountain ranges is interrupted occasionally by several old blocks of strata that have been folded, faulted, and deeply dissected. These ancient massifs now form either low platforms or high plateaus. The westernmost of these, the Shan Plateau of eastern Myanmar, measures some 250 miles (400 km) from north to south and 75 miles from east to west and has an average elevation of about 3,000 feet. The largest of these features is the Korat Plateau in eastern Thailand and west-central Laos. This area actually is more of a low platform, which on average is only a few hundred feet above the floodplains of the surrounding rivers. It consists of a string of hills that direct surface drainage eastward to the Mekong River. The hills range in elevation from 500 to 2,000 feet, with the highest altitudes occurring near the southwestern rim. The broad river valleys between the uplands and the even wider deltas at the southernmost points contain most of the mainland’s lowland areas. These regions generally are covered with alluvial sediments that support much of the mainland’s cultivation and, in turn, most of its population centers. The most extensive coastal lowland is the lower Mekong basin, which encompasses most of Cambodia and southern Vietnam. The Cambodian portion is a broad, bowl-shaped area lying just above sea level, with numerous hill outcrops jutting above the landscape; at its center is a large freshwater lake, the Tonle Sap. To the south the river’s vast, flat delta occupies the entire southern tip of Vietnam. Outside the river deltas, the coastal lowlands are little more than narrow strips between the mountains and the sea, except around the southern half of the Malay Peninsula. The Malay Peninsula stretches south for some 900 miles from the head of the Gulf of Thailand (Siam) to Singapore and thus extends the mainland into insular Southeast Asia. The narrowest point, the Isthmus of Kra (about 40 miles wide), also roughly divides the peninsula into two parts: the long linear mountain ranges of the northern part described above give way just south of the isthmus to blocks of short, parallel ranges aligned north-south, so that the southern portion trends to the southeast and becomes much wider. In areas such as the west coast between southern Thailand and northwestern Malaysia, distinctive karst-limestone landscapes have developed. Peaks on the peninsula range from 5,000 to 7,000 feet in elevation.

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