8th grade science

Hey students, it's Miss LeBlanc. I have a flu, so I'll be out the next two days and you guys are going to be watching videos and completing guided reading. More than 150 million years ago. During the Jurassic period, earth was nothing like it is today. The landscape was different. The climate was different, and the creatures that roamed the earth were very, very different. The brachiosaurus, or arm lizard, was one of many creatures that lived during this time. Rocky's sores gets its name from its long forelegs, which looked a little like arms. It is one of the largest known animals ever to live on land. But until 100 years ago, we didn't know anything about this dinosaur. In 1907, a German engineer was searching for minerals in eastern Africa when he stumbled on thousands of bones of ancient creatures. Hundreds of people excavated this area, known as tinda guru near the coast of Tanzania in Africa for 5 years. During that time, they unearthed 250 tons of fossils. The fossils were sent to the Humboldt museum in Germany. It took 20 years to sort and assemble the fossils before they were finally displayed. Her most impressive find was one of the biggest, most complete skeleton of a dinosaur ever found. The prehistoric rocky asaurus. Not only did this massive excavation effort uncover dinosaur fossils, it also unearthed the mystery. 30 years earlier, phones of another brachiosaurus had been dug up thousands of kilometers away. In Colorado. Scientists were baffled. It was unlikely that two identical creatures could have developed at the same time in two different parts of the world. And a dinosaur that lived on land could not have swum across the vast ocean between Africa and North America. But what if that ocean had not always been there? What if Africa and North America had once been joined together in a single landmass, so that brachiosaurus could just walk from one part to another. Over the last 100 years, scientists have developed a theory that answers these questions and solves the mystery of brachiosaurus. The theory of plate tectonics revolutionized our view of how the continents and oceans formed and changed over hundreds of millions of years. How do you think that bones of the same type of dinosaur ended up in two distant parts of the world? As you watch the following segment, think about the effects of moving plates on earth's surface. The landmasses on earth were once very different from the way they are today. Earth's surface is in constant motion and the continents are no exception. They are part of tectonic plates that move about two or three centimeters a year. About as fast as our fingernails grow. Over millions of years, new landmasses are made, some relocate, and others break up. The theory of plate tectonics explains how landmasses move. The earth is like an egg. The yolk is the core. The white is the mantle, and the comparatively thin shell is the earth's crust. The top layer of the mantle, together with the crust, is called a lithosphere. The lithosphere is broken up into about a dozen tectonic plates that hold all of the earth's continents and the ocean floor. The place move continuously in response to slow moving convection currents in the mantle. Land is pulled apart, shoved together, and reshaped. The theory of plate tectonics explains how it's possible to find evidence of similar plants and animals like the giant brachiosaurus on different continents. 250 million years ago, the plates jam together and form one huge supercontinent called pangea, which means all land. But over millions of years, the huge continent split and the modern continents gradually began to take shape. Oceans two were created when pangaea broke up. The Atlantic Ocean was formed when Africa and the Americas pulled apart. The giant continent of pangaea is hard to imagine, but one look at the shorelines of Africa and South America makes it easy to see how they once fit together. The boundaries between earth's tectonic plates are where all the action is. These cracks in the crust are called plate boundaries, and most lie under the oceans. At the mid ocean ridge, molten magma rises from the mantle. When it cools, the magma makes new oceanic crust. Plate boundaries both on land and under the water are also the places where most volcanos form. The red dots on this map represent volcanic activity around the globe. Each volcanic line marks boundaries between tectonic plates. Some plate boundaries are visible on land, like the San Andreas fault in California. The land around the fault is one of the most earthquake prone areas on the planet. Here, plates try to move past each other and they sometimes get stuck. When they become unstuck, the movement that results is an earthquake. When tectonic plates collide, mountains may be created in the process. The Himalayas earth's tallest mountain range are relatively young. The collision between India and the Eurasian plate pushed up these towering peaks only 30 million years ago. The look of our planet is constantly changing. Brachiosaurus bones found continents apart have helped us understand earth's dramatic past. What are earth's glands? How do plate movements affect earth's continents and oceans? October 17th, 1989. It was a balmy fall afternoon in San Francisco. People heading home from work. Kids playing after school sports. And 62,000 lucky fans gathered a candlestick park to watch the third game of the World Series. The battle of the bay continues, game three of the 1989 World Series, the Oakland athletics. Against the San Francisco Giants. I'm Al Mike. But in a split second, the calm turned into chaos. It was an earthquake. The biggest in 75 years, violently shaking the earth underfoot. Because of its geographic location, San Francisco has a long history of earthquakes, but nothing had prepared residents for a quake like this one. Forces deep underground sent out a burst of energy, powerful enough to topple more than 2000 buildings. And look out in the crack just suddenly opened up, and it just was so quick it was just like a rifle shot at just boom, it was open. In just 20 seconds, it was all over. But the awesome destructive power of the earthquake left devastation across much of the San Francisco Bay Area. What do you think causes earthquakes? As you watch the following segment, think about why the San Francisco Bay Area is so prone to earthquakes. In less than a minute, a 7.2 magnitude earthquake changed the face of San Francisco and the lives of all who lived there. The quake killed 63 people and cost the city $6 billion. We've had serious problems obviously. Go home and secure your residents. Shut off the gas. Shut off electricity, store water, prepare for aftershocks, prepare for three days in those services. San Francisco is one of the most earthquake prone cities in the world because of the ground it's built on. It sits on the edge of the San Andreas fault, a 1200 kilometer gash in the ground that marks the boundary between two tectonic plates or sections of the earth's crust. These plates are in slow but constant motion. The San Andreas is a strike slip fault, meaning the plates are moving in opposite directions. When the plates get stuck, the energy builds up. At a critical point, the plates lurch past each other, releasing energy and causing seismic waves. We feel those seismic waves as an earthquake. The focus of the San Francisco earthquake was 96 kilometers away, and 18 kilometers underground. But as the seismic waves traveled through the ground in all directions, they shook the earth as far as 350 kilometers away. In just moments, the seismic waves reached San Francisco. The primary ways or P waves which travel faster through the ground arrived first, causing the initial jolt. Then the secondary waves or S waves arrived, causing the ground to sway and rumble. It is these sheer S waves with their side to side and up and down motions that destabilize the ground enough to topple buildings, destroy roads and bridges, and ultimately cause the most damage. After the quake, parts of the city were unrecognizable. Buildings rested on top of cars. Homes lay in ruins. First gas lines fueled raging fires. And broken water mains flooded the streets. The Oakland bridge across the bay was badly damaged. And on the Oakland side, the upper level of a double decker highway collapsed on top of the lower level, trapping people below. Is absolutely unbelievable. People scrambling. People running up to the fire engine just an amazement of what had occurred and please help and people trap. Some of the worst damage in San Francisco was in the fashionable marine district. Here the homes were built on land, dredged from San Francisco Bay. Unstable ground even under normal circumstances, but especially dangerous during an earthquake. It's called liquefaction. During the earthquake, the S waves caused the earth under these buildings to shake so violently that it turned into quicksand. These homes didn't stand a chance. In the 20th century alone, earthquakes killed more than 2 million people. In the thousands of years that people have been trying without success to predict earthquakes, we still don't know when and where the next one will hit. But one thing is almost certain. Each year, somewhere on earth, a massive earthquake will strike a populated area and cause extensive damage and loss of life. Since scientists can't stop quakes or even predict them, they're working on ways to help people survive them. The best way to do that is to keep structures intact. In San Francisco, work has already begun on shoring up all the buildings and bridges in the area. The fancy name for this process is seismic retrofitting. The key to seismic retrofitting is to make structure stronger while still allowing them to move. Movement is vital for a structure survival because during an earthquake, when seismic waves hit, it must be able to absorb the impact of the shaking ground. These days, engineers rely on computers to figure out how much movement is necessary for the safety of different structures. High-tech systems show engineers wear failures might occur and help them design against disaster. Because the bay bridge sustains such extensive damage in the 1989 quake, San Francisco's bridges were an obvious place to start. On these bridges, rivets are being replaced by high strength bolts. Steel plates are being added to the towers. And the bases of many bridges are getting additional support. Engineers hope their earthquake proofing efforts will ultimately save lives. How do the different seismic waves travel? 1973, Iceland. A crack in the earth opens up and a column of fire shoots toward the clouds. In just days, homes many kilometers away are buried in black ash up to their roofs. In 1983, Hawaii. Kilauea sends a molten river of lava down a mountain, devouring everything in its path. 1980, Washington state. Mount St. Helens sends up a mushroom cloud of smoke and ash that turns day into night. It's no wonder that for thousands of years, volcanos were the stuff of myth and legend. The Romans believed that the fire God Vulcan worked his forge under the mountains. For the Hawaiians, the God is Pelé controlled fire. Over time, science has replaced mythology and our understanding of earth has grown. While we still respect earth's awesome forces, we have uncovered many of the secrets of volcanos. A volcano is a window into the red hot world a few kilometers below. All volcanos begin when molten magma rises through the denser material of the earth's mantle toward the planet's outermost solid layer or crust. There it can get trapped under layers of rock, forming what is known as a magma chamber. The magma simmers under great pressure for months. Years or even centuries. With a great roar, a plume of fire shoots toward the sky. All it takes is a crack or a weak spot in The Rock above and the magma explodes outward in the form of burning lava. Lava streams down the mountain and hardens, creating a landscape of black volcanic rock. Though much about volcanos is no longer a mystery, they can still strike awe in all who witnessed their tremendous power. What forces do you think are responsible for volcanos? As you watch the following video, think about volcanos you may have seen in television or in the movies. Hawaii's big island. It's a tropical Paradise of palm trees, sand, and sun. But it's even hotter than it looks. In the heart of this island is kilauea, the world's most active volcano. Kilauea's lava and lava from the island's older volcanos, mauna Kea and mauna loa, built this island, and it's still growing. It all started here deep below. The bottom of the ocean. A hotspot in the earth's mantle sends molten magma through the earth's crust. Over time, lava flows on the big island have produced a mountain taller than Mount Everest. If you measure from the sea floor, all of the Hawaiian Islands were formed in this way. A volcano is one way that the heat inside the earth is released. The heat moves in the form of gushing lava which flows freely and swelling waves down the mountain, and in this case into the ocean. Kilauea is known as a shield volcano because of the way its fluid, basaltic lava builds up layer upon layer, spreading out in the form of a shield. Lava from kilauea flows freely because it is low in silica and its temperature is high. As the lava flows, anything in its path goes up in flames. Kilauea's current eruption began in 1983 and shows no signs of stopping. Its lava hardens into acres of new land every year. Kilauea's volcanic power comes from a hotspot in the earth's mantle. But shield volcanos are not the most common or the most explosive kind of volcano. Mount Vesuvius outside the city of Naples in Italy is an example of a composite volcano, composite volcanos alternate between quiet and extremely explosive eruptions. It sits near the boundary of two of earth's tectonic plates. Occupying a weak spot that lets magma from the mantle rise to the surface in a very dramatic way. On August 24th, 79 AD, an enormous chamber of magma, far under Mount Vesuvius, burst through its cone. The mountain's peak literally blew off. The thriving Roman cities of herculaneum and Pompeii lay at the foot of the mountain, over 50,000 people lived there. And explosive eruption called a pyroclastic flow hurled out rock, poisonous gas, and scalding ash. Buildings offered no refuge. They erupted in flames. In all, more than 16,000 people were killed. The volcano's victims were locked in time by the hot ash. Their anguish preserved in moles left by their bodies. A column of smoke and ash hovered high above the city of Pompeii. Days later, rain fell, setting the ash like concrete and entombing the city until the 18th century when the eerie scene came to light. Since this catastrophic eruption, Vesuvius had spit and sputtered, lava and ash, but not with a deadly force of nearly 2000 years ago. The next big eruption though might be just around the corner. Shield and composite volcanos form slowly over many years. A third kind of volcano called cinder cones, can emerge in just a few years. That's exactly what happens in a small Mexican village of paricutin in 1943. A crack appeared in a cornfield. It began belching smoke and ash. This process marked the birth of a cinder cone volcano. A cinder cone volcano is a steep cone shaped hill made of volcanic ash and cinders that build up around the volcano's opening. Paricutin is pile of rock and ash began to rise. Within a day, a cone measured 12 meters high, a new volcano was born. Within a week, the cone rose a 152 meters. After a year, the volcano had risen to 366 meters. It continued to grow even worse. It continued pouring out ash. 9 years after it was born, para cooten covered almost 15 km² of rain. Then the eruption slowed and stopped. But not before whole villages had to be evacuated. It has not erupted since, but it's not dead either. At any moment, paricutin could erupt again. A volcano can have a lifespan of over a million years. Unpredictable, it can like dormant for hundreds of years, then explode, sleep for another few hundred years, and then erupt again. Why do you think a dormant volcano could still be dangerous?