55 L6-Earth Then and Now

Oxford Read and Discover level 6 Earth Then and Now by Robert Quinn

《牛津阅读与发现》第6级《地球的过去与现在》作者:罗伯特·奎因

Introduction Did you know that Earth formed billions of years ago? Our planet has changed a lot since then. The oceans and continents have moved. The plants and animals that we see today were not always here— some are old and some are new. People are new, too. Scientists say that we have only been here for about 200,000 years! How did Earth form? When did plants and animals first appear? Where did the first people live on Earth? How do oceans and continents move? What keeps Earth warm? Discover! Now read and discover more about Earth in the past and Earth today!

你知道地球是几十亿年前形成的吗? 从那时起，我们的星球发生了很大的变化。 海洋和大陆都在移动。 我们今天看到的植物和动物并不总是在这里——有些是古老的，有些是新的。 人们也是新来的。科学家说我们在地球上只存在了大约20万年!地球是如何形成的? 植物和动物最早是什么时候出现的? 地球上最早的人类生活在哪里? 海洋和大陆是如何移动的? 是什么让地球保持温暖?发现!现在阅读和发现更多关于地球的过去和今天!

Chapter 1 A Ball of Fire Scientists think that Earth is about 4.6 billion years old. Our planet started as an enormous ball of fire! How Earth Formed Scientists think that Earth formed from a cloud of gas, dust, and rock that was around our sun. These materials came together and formed a ball of fire and liquid rock. At that time, the temperature on Earth's surface was very hot, and nothing lived here. Discover! The Great Pyramid in Egypt is about 4,600 years old. Earth is one million times older than that! Earth's Layers After millions of years, Earth cooled down. The surface became a layer of solid rock, called the crust. This is the part of Earth that we live on. The crust is usually about 30 kilometers thick on land, but it's thinner at the bottom of the ocean. Under Earth's crust, there's a layer called the mantle. It's about 2,900 kilometers thick. The mantle is very hot its temperature is about 3,000 degrees centigrade. It's mostly made of liquid rock, called magma. Earth's core is under the mantle, at the center of the planet. The core is about 3,500 kilometers across and it's mostly made of two metals iron and nickel. The outer core is liquid, but the inner core is solid. That's because the other layers push down on the inner core with incredible pressure. Temperatures in the inner core can be more than 6,000 degrees centigrade.

科学家们认为地球大约有46亿年的历史。 我们的星球最初是一个巨大的火球!科学家们认为地球是由太阳周围的气体、尘埃和岩石组成的云形成的。 这些物质聚集在一起，形成了一个火球和液态岩石。 那时，地球表面的温度非常高，没有生物在这里生存。 发现!埃及的大金字塔大约有4600年的历史。 地球的年龄是它的一百万倍!几百万年后，地球冷却下来。 表面变成了一层坚硬的岩石，称为地壳。 这是我们生活的地球的一部分。 陆地上的地壳通常厚约30公里，但海底的地壳要薄一些。 在地壳之下，有一层叫做地幔。 它大约有2900公里厚。 地幔非常热，温度约为3000摄氏度。 它主要由液态岩石构成，也就是岩浆。 地核在地幔之下，在地球的中心。 地核直径约3500公里，主要由铁和镍两种金属组成。 外核是液体，而内核是固体。 这是因为其他层对内核施加了巨大的压力。 内核的温度可以超过6000摄氏度。

Mountains of Fire There's a lot of heat in Earth's core and mantle. We can see some of this heat when volcanoes erupt and produce lava. In some parts of Earth's crust, magma forms underground pools, called magma chambers. When there's a lot of magma in a chamber, the magma moves up a tunnel to the surface. When the magma gets to Earth's surface, it's called lava. The lava comes out of holes called vents. Some volcanoes also produce lots of gas and ash. The lava and the ash can sometimes form a tall cone. Discover In 2010, a volcano in Iceland erupted and produced big clouds of ash. Planes couldn't fly through the ash, so thousands of people couldn't travel! Underwater Volcanoes Sometimes volcanic vents form under the ocean. When this happens, the lava cools very quickly and makes round shapes, called pillow lava. Underwater lava can also build up and form volcanic islands, like Iceland or Hawaii. One of the newest volcanic islands on our planet is Hunga Ha'apai, near Tonga in the Pacific Ocean. This island appeared after a big underwater eruption in 2009.

地核和地幔中有很多热量。 当火山喷发并产生熔岩时，我们可以看到一些热量。 在地壳的某些部分，岩浆形成地下池，称为岩浆库。 当岩浆室中有很多岩浆时，岩浆会沿着隧道向上移动到地表。 当岩浆到达地球表面时，它被称为熔岩。 熔岩从喷口流出。 一些火山还会产生大量的气体和灰烬。 熔岩和火山灰有时会形成一个高高的圆锥体。 2010年，冰岛的一座火山爆发，产生了巨大的火山灰云。 飞机无法穿过火山灰，所以成千上万的人无法出行!海底火山有时在海底形成火山口。 当这种情况发生时，熔岩会迅速冷却，形成圆形，称为枕状熔岩。 水下熔岩也可以形成火山岛，就像冰岛或夏威夷一样。 位于太平洋汤加附近的Hunga Ha'apai是地球上最新出现的火山岛之一。 这个岛是在2009年的一次水下大喷发之后出现的。

Chapter 2 Water and Air Today, water covers about 70% of our planet. Billions of years ago, Earth's surface was dry, and nothing lived here. Earth's atmosphere was also different. It had lots of carbon dioxide and other gases, but no oxygen. How the Oceans Formed At first, there wasn't any liquid water on Earth's surface, but there was lots of water vapor in the atmosphere. This water vapor came from inside the planet when volcanoes erupted. When Earth cooled down, the water vapor condensed and formed clouds in the sky. Then it started to rain. After millions of years, liquid water covered most of our planet's surface! Discover Some of our planet's water came from millions of icy meteorites. When the meteorites entered Earth's atmosphere, the ice heated up and changed to water vapor. Oxygen About 3 billion years ago, something amazing happened living things appeared on Earth! Some of the first living things were tiny blue-green bacteria. These bacteria grew in shallow pools of warm water and we can find their fossils today. The fossils look like rocks with unusual shapes and they're called stromatolites. Blue-green bacteria used sunlight, water, and carbon dioxide to make their own food, like plants do today. The blue-green bacteria also produced oxygen, and after millions of years, there was lots of oxygen in Earth's oceans and atmosphere. Today, the air that we breathe is about 21% oxygen. We couldn't live without it!

今天，水覆盖了地球的70%。 数十亿年前，地球表面干燥，没有生物在此生存。 地球的大气层也不同。 它有很多二氧化碳和其他气体，但没有氧气。 海洋是如何形成的起初，地球表面没有液态水，但大气中有大量的水蒸气。 当火山爆发时，这些水蒸气来自地球内部。 当地球冷却下来时，水蒸气凝结形成了天空中的云。 然后开始下雨了。数百万年后，液态水覆盖了地球的大部分表面!我们星球上的一些水来自数百万颗冰冷的陨石。 当陨石进入地球大气层时，冰被加热并变成水蒸气。 大约30亿年前，神奇的事情发生了地球上出现了生物!最早的一些生物是微小的蓝绿色细菌。 这些细菌生长在温暖的浅水池中，我们今天可以找到它们的化石。 这些化石看起来像形状不寻常的岩石，它们被称为叠层石。 蓝绿色细菌利用阳光、水和二氧化碳来制造自己的食物，就像今天的植物一样。 蓝绿色的细菌也会产生氧气，数百万年后，地球的海洋和大气中有了大量的氧气。 今天，我们呼吸的空气中大约有21%是氧气。 没有它我们活不下去!