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Astronomy - Earth and its Moon

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    Study Guide Astronomy – Earth and its Moon 1. Earth's Atmosphere Earth is surrounded by a thick blanket of gases called the atmosphere . This atmosphere protects life and controls weather and temperature. Scientists divide the atmosphere into four main layers , based on how temperature changes with height. 1.1 The Troposphere (Lowest Layer) The troposphere is the lowest layer of the atmosphere and is closest to Earth’s surface. This is the layer where we live and where weather occurs . • Air in this layer is constantly moving due to convection currents • This movement causes clouds, rain, winds, and storms • Air density decreases quickly as height increases • The main source of heat is conductive heating from the ground • Heat is lost through radiation and mixing of air Because of these processes, temperature decreases rapidly as altitude increases in the troposphere. 1.2 The Stratosphere Above the troposphere lies the stratosphere . • This layer contains strong horizontal winds , known as the jet stream • These winds influence weather patterns at Earth’s surface • Ozone gas in this layer absorbs harmful ultraviolet (UV) radiation from the Sun As a result, the stratosphere plays a major role in protecting life on Earth .

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    Study Guide 1.3 The Mesosphere Above the stratosphere is the mesosphere . • Oxygen and ozone absorb solar ultraviolet radiation • Energy is lost through radiation and air mixing • At the base of the mesosphere, around 50 km above Earth , temperature reaches a local maximum This balance between energy gain and loss defines the mesosphere. 1.4 The Thermosphere and Ionosphere The thermosphere lies above the mesosphere. • Very short - wavelength solar radiation is absorbed here • There are very few air particles, so absorbed energy leads to very high temperatures The lowest part of the thermosphere (from about 80 km to 400 km ) is called the ionosphere . • Gases are ionized by solar radiation • This layer reflects radio waves , helping long - distance communication • Meteors burn up in this region Far above this, the exosphere slowly fades into outer space.

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    Study Guide 1.5 The Coriolis E ff ect and Global Weather Earth rotates on its axis, and this rotation affects air movement. • All points on Earth rotate once every 24 hours • The equator travels faster than the poles • Air moving north or south keeps its original eastward speed This causes the Coriolis Effect , which makes air appear to curve: • In the Northern Hemisphere , air moving toward low pressure rotates counterclockwise • In the Southern Hemisphere , it rotates clockwise • Air moving away from high pressure rotates clockwise in the Northern Hemisphere This effect plays a major role in winds, storms, and hurricanes . 1.6 Importance of the Atmosphere The atmosphere is essential for life because it: • Reduces extreme temperature changes across the planet • Protects Earth from harmful ultraviolet radiation • Supplies essential gases like oxygen and carbon dioxide • Helps maintain a stable climate 1.7 The Magnetosphere The magnetosphere is the region of space around Earth controlled by Earth’s magnetic field . • It protects Earth from harmful charged particles from the Sun • Inside it are two doughnut - shaped regions called the Van Allen belts • These belts trap charged particles from the solar wind Some of these particles travel along magnetic field lines and enter the atmosphere near the poles, creating the aurora (Northern and Southern Lights). The solar wind stretches the magnetosphere into a long tail opposite the Sun .

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    Study Guide Other planets with magnetic fields also have magnetospheres. 1.8 The Greenhouse E ff ect Earth is warmer than expected because its atmosphere traps some heat . • Sunlight heats Earth’s surface • The surface gives off heat as thermal radiation • Some of this heat is absorbed and re - emitted by atmospheric gases This process is called the greenhouse effect . Gases that contribute to this effect include: • Carbon dioxide (CO ₂ ) • Water vapor (H ₂ O) • Methane (CH ₄ ) • Chlorofluorocarbons (CFCs or freons) Because of the greenhouse effect, Earth’s average temperature is about 300 K (80°F) instead of 250 K . Venus shows an extreme example of this effect due to its very dense CO ₂ atmosphere .

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    Study Guide Summary • The atmosphere has four main layers • Weather happens in the troposphere • UV protection comes from the stratosphere • Meteors burn in the thermosphere • The magnetosphere shields Earth from solar wind • The greenhouse effect keeps Earth warm enough for life 2. Earth's Chemical Composi Ɵ on 2.1 What Is Earth Made Of? Earth is made up of different materials, both in its atmosphere and inside the planet itself . Scientists study these materials to understand how Earth formed and how it works today. 2.2 Composi Ɵ on of Earth’s Atmosphere The atmosphere is the layer of gases surrounding Earth. Its composition is fairly stable and includes: • 78% nitrogen (N ₂ ) • 21% oxygen (O ₂ )

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    Study Guide • 1% argon (Ar) In addition to these main gases, there are very small (trace) amounts of: • Carbon dioxide • Water vapor • Other gases Even though these gases are present in small amounts, they play an important role in weather, climate, and life on Earth. 2.3 Chemical Composi Ɵ on of Earth’s Surface Rocks When scientists directly analyze rocks found on Earth’s surface, they discover that they are mainly made of the following elements, listed from most to least abundant: 1. Oxygen 2. Silicon 3. Aluminum 4. Iron These surface rocks have an average density of about 2.7 g/cm³ , meaning they are relatively light compared to Earth as a whole. 2.4 Earth’s Density: A Big Clue Although surface rocks are not very dense, the average density of the entire Earth is much higher — about 5.5 g/cm³ . This difference leads to two very important conclusions. 2.5 What Does This Tell Us About Earth’s Interior? The Inside of Earth Is Much Denser The high overall density means Earth’s interior must contain much heavier materials than those found at the surface. • The pressure from overlying rocks does compress materials inside Earth. • However, compression alone is not enough to explain the high density. • This means Earth’s interior must contain naturally dense elements , especially iron and nickel , which are also common in the universe.

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    Study Guide 2.6 Earth Was Once Very Hot and Molten The clear separation between: • lighter materials on the outside , and • heavier materials in the center suggests that early in Earth’s history, the planet was partially or fully molten . When Earth was hot and molten: • Heavy elements like iron and nickel sank toward the center . • Lighter materials rose toward the surface . This process is called chemical differentiation , and it explains why Earth has layered internal structures today. Key Takeaway Earth’s chemical composition — both at the surface and deep inside — gives us strong evidence that the planet: • Has a dense, metal - rich interior , and • Went through a hot, molten phase early in its history These insights help scientists understand not just Earth, but how other planets may have formed as well. 3. Interior Structure: Core, Mantle, Crust 3.1 How Do We Study Earth’s Interior? We cannot directly see or drill deep into the Earth. Instead, scientists study earthquake waves to learn about what lies inside our planet. When an earthquake occurs near the Earth’s surface, it sends out two main types of waves: • Pressure (P) waves , which move back and forth • Transverse (S) waves , which move side to side

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    Study Guide As these waves travel through the Earth, their paths bend due to refraction , because different layers have different densities and properties. By carefully measuring the arrival times of these waves at seismographic stations around the world, scientists can determine the density, temperature, and pressure inside the Earth. 3.2 Main Layers of the Earth Earth has three major internal layers: 1. Crust 2. Mantle 3. Core Each layer has unique physical and chemical properties. 3.3 The Crust The crust is the thin outermost layer of the Earth. It includes: • Continents • Ocean floors Even at its thickest, the crust is only about 30 kilometers deep , which is very thin compared to Earth’s total size. 3.4 The Mantle Beneath the crust lies the mantle , which is much thicker and denser. • The uppermost mantle behaves like a solid and, together with the crust, forms the lithosphere , which is about 80 kilometers thick . • Below this lies the asthenosphere , where mantle rocks are plastic or malleable . • This means the material can slowly flow under pressure , even though it remains solid.

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