Earth Systems

Grade 8 Science Worksheets

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Looking inside the Earth

The outside layer of Earth cooled down a long time ago and became solid rock. This is called the crust. We all live on this crust. Even the oceans are on this crust. Way below the crust is the mantle that gets hotter and hotter the deeper into the Earth you go. Below the mantle are two more layers called cores, the outer core and the inner core. The outer core is made of hot, melted metal. The inner core, which is at the center of the Earth, is a solid ball of hot metal.

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Water and Air

The land on which we live is less than 30% of the crust of Earth. More than 70% is made up of water in the form of oceans and seas. Water is essential to life, as is air, or atmosphere.

99% of our atmosphere is made up of essential gases, Nitrogen, and Oxygen, which we need for breathing. The rest consists of water vapor and some other gases like Carbon Dioxide.

A Moving Earth

The Earth’s crust is made up of tectonic plates that are slowly but constantly moving on top of the liquid mantle. Sometimes these plates meet head-on and clash, breaking the crust and sending ripples and quivers all around. We feel these tremors and call it an earthquake.

Often, this molten rock rises up thru the crust and forms new layers on top of the ground. This hot metal called magma pours out on the open surface in the form of lava. Layers and layers of hot lava build one on top of the other over time to form a special kind of mountain named a volcano. Some volcanoes still erupt with hot molten lava from time to time.

Building and Rebuilding the Earth

Erupting magma is responsible for forming islands, mountains, volcanoes, even new layers of land and continents. The rocks in the earth’s crust tell us the entire history of the earth over its life of 4 ½ billion years. Apart from plate tectonics, the earth also changes due to weathering and erosion. Destructive elements such as ice, wind, water and changing temperatures break up the crust creating sediments. Sediments from strata on the earth’s surface. By studying these sediment layers, we are able to determine how the earth was formed over billions of years.

The major time periods on earth are called Eras, each of which has lasted for several million years. We name the eras as follows: 

  1. Precambrian Era
  2. Paleozoic Era
  3. Mesozoic Era
  4. Cenozoic Era

Check Point

  1. Name the layers of the Earth from outside to inside.
  2. Name the two major gases in our atmosphere.
  3. The Earth’s crust is made up of ______ plates.
  4. Name the major time periods on Earth.
  5. A ______ is a special kind of mountain which erupts with a hot liquid metal called magma.

Answer Key

  1. The crust, Mantle, Outer Core, Inner Core
  2. Nitrogen and Oxygen
  3. Tectonic
  4. Precambrian, Paleozoic, Mesozoic and Cenozoic Eras
  5. Volcano

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