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Meteorology Science that studies the Earth’s atmosphere Evolution of the Earth’s Atmosphere State Standard #8b Students know how the composition of Earth’s atmosphere has evolved over geologic time and the effect of out gassing, the variations of carbon dioxide concentration, and the origin of atmospheric oxygen. Atmosphere- envelope of gases that surround earth. Formation of the Earth’s Atmosphere First Atmosphere • Composition - Probably H2, He • These gases are relatively rare on Earth compared to other places in the universe and were probably lost to space early in Earth's history because – Earth's gravity is not strong enough to hold lighter gases – Earth still did not have a differentiated core (solid inner/liquid outer core) which creates Earth's magnetic field (magnetosphere = Van Allen Belt) which deflects solar winds. • Once the core differentiated the heavier gases could be retained • The history of the Earth's atmosphere prior to one billion years ago is poorly understood, but the following presents a plausible sequence of events. This remains an active area of research. • The modern atmosphere is sometimes referred to as Earth's "third atmosphere", in order to distinguish the current chemical composition from two notably different previous compositions. The original atmosphere was primarily helium and hydrogen; heat (from the still molten crust, and the sun) dissipated this atmosphere. • About 3.5 billion years ago, the surface had cooled enough to form a crust, still heavily populated with volcanoes which released steam, carbon dioxide, and ammonia. This led to the "second atmosphere"; which was, primarily, carbon dioxide and water vapor, with some nitrogen but virtually no oxygen. (Though very recent simulations run at the University of Waterloo and University of Colorado in 2005 suggested that it may have had up to 40% hydrogen. (http://newsrelease.uwaterloo.ca/news.php?id=4348)) This second atmosphere had ~100 times as much gas as the current atmosphere. It is generally believed that the greenhouse effect, caused by high levels of carbon dioxide, kept the Earth from freezing. • During the next few billion years, water vapor condensed to form rain and oceans, which began to dissolve carbon dioxide. Approximately 50% of the carbon dioxide would be absorbed into the oceans. One of the earliest types of bacteria are the cyanobacteria. Fossil evidence indicates that these bacteria existed approximately 3.3 billion years ago and were the first oxygen producing evolving phototropic organisms. They are responsible for the initial conversion of the earth’s atmosphere from an anoxic (state without oxygen) to an oxic (with oxygen) state. Being the first to carry out oxygenic photosynthesis, they were able to convert carbon dioxide into oxygen playing a major role in oxygenating the atmosphere. • Photosynthesizing plants would evolve and convert more carbon dioxide into oxygen. Over time, excess carbon became locked in fossil fuels, sedimentary rocks (notably limestone), and animal shells. As oxygen was released, it reacted with ammonia to create nitrogen; in addition, bacteria would also convert ammonia into nitrogen. • As more plants appeared, the levels of oxygen increased significantly (while carbon dioxide levels dropped). At first it combined with various elements (such as iron), but eventually oxygen accumulated in the atmosphere — resulting in mass extinctions and further evolution. With the appearance of an ozone layer (ozone is an allotrope of oxygen) lifeforms were better protected from ultraviolet radiation. This oxygen-nitrogen atmosphere is the "third atmosphere". Formation of the Earth’s Atmosphere • Second Atmosphere • Produced by volcanic out gassing. • Gases produced were probably similar to those created by modern volcanoes (H2O, CO2, SO2, CO, S2, Cl2, N2, H2) and NH3 (ammonia) and CH4 (methane) • No free O2 at this time (not found in volcanic gases). • Ocean Formation - As the Earth cooled, H2O produced by out gassing could exist as liquid in the Early Achaean, allowing oceans to form. – Evidence - pillow basalts, deep marine seds in greenstone belts. Atmospheric Out gassing Out gassing- process by which gases within the Earth were released during its formation. Formation of the Earth’s Atmosphere Addition of O2 to the Atmosphere • Oxygen Production – Photochemical dissociation - breakup of water molecules by ultraviolet • Produced O2 levels approx. 1-2% current levels • At these levels O3 (Ozone) can form to shield Earth surface from UV – Photosynthesis - CO2 + H2O + sunlight = organic compounds + O2 - produced by cyanobacteria, and eventually higher plants - supplied the rest of O2 to atmosphere. Thus plant populations • Oxygen Consumers – Chemical Weathering - through oxidation of surface materials (early consumer) – Animal Respiration (much later) – Burning of Fossil Fuels (much, much later) Chapter 22-1 Atmospheric Composition Purpose of the Atmosphere Early Earth would have been very different and inhospitable compared to the Earth today. • Hot – Why? - Primordial heat, collisions and compression during accretion, decay of short-lived radioactive elements – Consequences - Constant volcanism, surface temperature too high for liquid water or life as we know it, molten surface or thin, unstable basaltic crust. • Atmosphere - early atmosphere probably completely different in composition (H2, He) • Cooling – Primordial heat dissipated to space – Condensation of water (rain), accumulation of surface water. – Accumulation of new atmosphere due to volcanic out gassing – Conditions appropriate for evolution of life It’s all about chemistry Chapter 22-1 Atmospheric Composition Why the Atmosphere The atmosphere surrounds Earth and protects us by blocking out dangerous rays from the sun. The atmosphere is a mixture of gases that becomes thinner until it gradually reaches space. It is composed of Nitrogen (78%), Oxygen (21%) and other gases (1%). Chapter 22-1 Atmospheric Composition Nongaseous components of air Water vapor- moisture in the air in the form of a gas. Water vapor in the air varies from place to place. Water vapor plays a very important role in weather. Particulate matter- tiny particles of dust, smoke, salt, pollen, smog and other chemicals. Chapter 22.1 Layers of the Earth’s Atmosphere. The atmosphere begins at the earth’s surface and goes more than 700 km up. Troposphere- layer of the atmosphere closest to the earth. Most water vapor is found here. 99% of all weather occurs here. Temperature drops with altitude. Stratosphere- second layer of the earth’s atmosphere. No weather occurs here. Airplanes travel in this layer. Strong, dry steady winds. Ozone is found here. Ozonosphere- Layer of the stratosphere that prevents U.V. rays from reaching the earth. Layers of the Earth’s Atmosphere Atmospheric layers Chapter 22.1 Layers of the Earth’s Atmosphere. Mesosphere- Third layer of the earth’s atmosphere. Temperatures decrease with an increase in altitude. Meteors burn-up Thermosphere- upper layer of the earth’s atmosphere. Temperature increases with an increase in altitude. Auroras occur in this region. Ionosphere- Zone of highly ionized (ions) particles. Radio waves can bounce off of this layer. Chapter 22.1 What is Air Pressure? Objective- Explain air pressure and describe what affects it. Newton- metric unit of force (f= mass x acceleration) Pressure- amount of force per unit of area. Weight is a force (mass acted upon by gravity). A force exerted over a small area causes more pressure than the same force applied over a large area. Atmospheric Air has weight. 1 L=.01 N @ sea level. Pressure is greatest at the Earth’s surface and decreases as altitude increases. Factors that affect Atmospheric Pressure Elevation Air pressure changes with elevation or height above sea level. Weight of the air press downward at the surface, forcing air molecules close together. Higher up the air molecules are further apart creating less pressure. The higher the elevation, the lower the air pressure. Factors that affect Atmospheric Pressure Water Vapor The more water vapor in the air, the lower the air pressure. Air with a lot of water vapor weights less than dry air. Thus moist air exerts less pressure. Atmospheric Weight (Atomic mass unit) Nitrogen= 14 Oxygen=16+16+32 Carbon dioxide= 12+16+16=44 Argon=40 H20=1+1+16=18 Temperature The higher the air temperature, the lower the air pressure. Warm air expands and is less dense. (Rising air) Cool air contracts and is more dense. (Sinking air) Factors that Affect Air Pressure Temperature Chapter 22.1 How is air pressure measured? Objective- Explain how a barometer measures air pressure. Barometer- instrument used to measure air pressure. Types of Barometers Mercury Barometers use a liquid, mercury, to measure air pressure. In 1643 Evangelista Torricelli devised the mercury barometer. The average sea level column of mercury is 760mm or 29.92 in. Types of Barometers Aneroid barometer do not use liquid. They are constructed with an airtight canister. As the canister expands, it indicates a low pressure. As the canister contracts, it indicates a high pressure. Measurements are recorded in millimeters of mercury Units of Measurement of air pressure All standard measurements are taken at sea level. 760mm of Mercury 29.92 inches of mercury 1013.2 mb (millibars-metric unit of measurement) Conversions 1 inch=34mb Measuring Altitude Altimeter- device used to measure altitude. Chapter 22.2 How is the Earth’s surface Heated? Objective- describe how energy from the Sun warms Earth’s surface. Radiant energy- energy given off by the Sun that can travel through space. Radiation- movement of the Sun’s energy through space. The warmth you feel on your skin is radiant energy from the sun. The movement of this energy through space is called radiation. Chapter 22.2 How is the Earth’s surface Heated? Absorption of Energy Dark surfaces absorb light. When light is absorbed it usually is changed to heat. Light colored surfaces reflect light an stay cool, dark colored surfaces absorb light and get warm. Energy from the Sun The Earth receives about 1 billionth of the energy that leaves the Sun’s surface. Reflected- bounces off the top of clouds. Absorbed- water droplets, dust particles absorb the energy. Atmospheric Heat Budget Chapter 22.2 How does heat move through the atmosphere? Objective; Explain how the atmosphere is heated. Heat moves through the atmosphere in three main ways: Conduction- transfer of heat through matter by direct contact. transfer of heat energy from one molecule to another molecule. Moves from an area of higher temperature to an area of lower temperature. Convection- process by which heat is transferred through liquids and gases. warm air is heated, it expands, it becomes lighter because it is less dense and rises. cooler air molecules move closer together (contract), become denser and sink. Energy transfer within the Earth’s atmosphere Radiation- Radiant energy is energy emitted from a single source (sun) is absorbed and changed into heat energy. Radiant energy is short wave energy. Heat energy is long wave energy. Earth’s surface absorbs energy but reradiates it back into the atmosphere, where it is absorbed by atmospheric gases. Greenhouse Effect- The process where the earth’s atmosphere traps earth’s re-radiated energy within the atmosphere, warming the earth. Chapter 22.3 How do winds form? Objective- Explain how winds form. Wind- horizontal movement of air. Air current- up-and-down movement of air. Wind Air is free to move in any direction. Vertical movement of air is called updrafts or downdrafts. Greater volumes of air move horizontally. Chapter 22.3 What causes local winds? Objective- Describe patterns of local winds. All winds are produced by temperature differences caused by unequal heating of the Earth’s surface. Local wind patterns are small scale winds produced by local changes in air pressure. Sea and Land breezes- produced when land heats up faster than water and when land cools off faster than water. Sea Breeze Land Breeze Local Wind Patterns Mountain and Valley Breeze- winds created by differential heating of mountains and valleys regions. Regions of rising air (low pressure), sinking air (high pressure) Mountain Breeze Valley Breeze Local Wind Patterns Monsoons- wind that changes direction with the seasons. Winter monsoon Summer monsoon Cool land surfaces, warm water Warm land surfaces, cool water Chapter 22.3 How is wind measured? Objective- Explain how weather instruments are used to describe wind. A wind is named for the direction from which it comes. Wind Vane- instrument that indicates wind direction. Wind sock can indicate direction and speed. Measuring Wind Anemometer- instrument that measures wind speed. Weather balloons are used to determine wind speed and direction. Wind speed Wind speed is determined by the velocity that air moves between a high and low pressure. Isobars- line on a weather map that connects equal points of pressure. Wind Speed Pressure Gradient- Rate at which air pressure changes on the shortest path between two isobars.
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