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2.Topic 6-Video 1

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Earth, a planet like none other ever discovered. Lush, tempered, and home to millions of species of plants, animals, under sea creatures, and human beings. Why is Earth teeming with life, when all the other planets in our Solar System appear lifeless. Welcome to Space School. Today's topic is our home, planet Earth, the largest of the Solar System's four rocky inner planets; the others Mercury, Venus and Mars. Earth is the only planet whose name in English is not derived from Greco Roman mythology. It comes from the Anglo-Saxon word for ground or soil, Erda. But, for us what makes Earth unique is that it is the only known place in the Universal that supports life. Earth was made out of what was leftover as the newly formed Sun cooled. Earth is the fifth largest planet in the Solar System, and is 4.6 billion years old. Our planet's only natural satellite, the Moon orbits nearly 239,000 miles up. The Earth and Moon are sometimes considered a planetary system, a double planet, due to the exceptionally large size of the moon, relative to its host planet. Earth's core is made up almost entirely of Iron. The inner core is solid, while the outer core is thought to be liquid. The next is a layer called the Mantle, made up of rock, much of it in a viscous or a semi-liquid state. The surface is formed by a thin rocky crust. Seven large plates and a few smaller ones are floating on the molten lava that forms the Mantle. These plates are constantly moving. The fastest, the Cocos plate of the west coast of Central America moves 75 millimeters per year, almost 25 feet every century. One of the keys to life on Earth is its atmosphere. As the newly formed Earth solidified, helium and hydrogen gas created a thin shield held in place by gravity. Over billions of years, our planet's atmosphere has evolved, first into one, rich in Carbon Dioxide, and, then into its present form, 78% Nitrogen, 21% Oxygen, and tiny amounts of Argon gas and Carbon Dioxide. Much of that changes been the result of Photosynthesis. First, bacteria, and, later, more complex plant life absorbed Carbon Dioxide and released Oxygen, making animal and human life possible. The Earth's atmosphere protects us in many ways. It blocks out the Sun's radiation, and, keeps in elements, we need to survive, mainly water and oxygen. It also protects us from being battered by meteors and asteroids, destroying them long before they reach the surface. Another key to our life on earth is our planet's rotation. When compared to another planets, Earth rotates rather quickly, completing one revolution every 24 hours. This means both day and night are short enough that temperatures don't fluctuate wildly. Earth orbits the Sun every 365 and a quarter, days. That extra quarter of a day is accounted for every 4 years, as a leap year. Without a leap year, eventually, the seasons would no longer correspond with our calendar. In just 730 years, Summer in the Northern Hemisphere, would arrive on December 21st. The four seasons are caused by the tilt of the Earth towards or away from the Sun, changing the angle and intensity of Sunlight falling on the Earth. That tilt also makes the Sun appear in different locations across the sky, throughout the year. Summer or Winter Solstice: The point in the orbit of maximum tilt toward or away from the Sun. The entire planet Earth is surrounded by a magnetic field caused by the molten iron core. The North and South poles work together to create a giant magnet that reaches thousands of miles into space. Amazingly, for reasons scientists still cannot explain, the polarity of the Earth's magnetic field, periodically switches. So, sometime in the future, all our compasses will point South, not North. Liquid water is key to life on Earth. Without it, we wouldn't exist. Luckily, it's also one of the most abundant resources here covering almost 75% of our planet's surface. Most is found in deep salt field oceans. Fresh water makes up just 3%. And, water on Earth exist as a solid, a liquid, and a gas. Only one eighth of the surface of the Earth is suitable for human habitation. Moisture in our atmosphere, combined with Solar Energy, is the primary cause of weather patterns. Our weather travels, because, uneven heating of our planet causes changes in air pressure forming wind currents. These wind currents carry moisture leading to everything from rain and blizzards, to tornadoes and hurricanes. Due to tremendous changes in the Earth's geology and atmosphere, weather has been dynamic throughout our geological history. We've had ice ages as well as warmer and dryer periods. But, today in the first time in human history, many scientists theorized that we are responsible for climate change. Industry and Automobiles release Carbon Dioxide, and major green house gas, trapping the Sun's energy, warming the Earth. Worse, development and deforestation has reduced the plant life that absorbs Carbon Dioxide. The impact of global warming is yet to be seen. But, no doubt, it can lead to melting ice caps, rising sea levels and severe changes in our weather. Whatever the future holds, we should all adopt a greener lifestyle, and limit our impact on this fragile and unique planet. Using less energy, recycling instead of throwing away, and replanting native shrubs and trees, all will help our planet survive and thrive. More than 6 billion human beings, and countless other species live on this planet. Yet, the Earth has many mysteries to reveal. From the depths of the oceans to remote jungles, to the very core of our planet, even today there remains much yet to be discovered. This is Space School, signing off. Class dismissed.

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Duration: 6 minutes and 26 seconds
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Language: English
License: Dotsub - Standard License
Genre: None
Views: 10
Posted by: pgtranscribes on Apr 23, 2015

2.Topic 6-Video 1

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