Formationof the Atmosphere • Most of the Earth’s early atmosphere was lost due to the vigorous solar wind from the early Sun. • Continuous volcanic eruptions built a new atmosphere of: • water vapor • carbon dioxide • nitrogen • methane
Formation of the Atmosphere • Comets brought water and organic molecules. • Oxygen did not appear in the atmosphere until after the first bacteria evolved. • Early plants released oxygen as a waste product and helped to build the atmosphere. • Once oxygen was present in the atmosphere, ozone could form, blocking out the Sun’s ultraviolet rays and changing the way life evolved.
The Atmosphere The Earth’s atmosphere (where pressure becomes negligible) is over 140 km thick. Compared to the bulk of the planet, this is an extremely thin barrier between the hospitable and the inhospitable. • Earth's atmosphere contains roughly: All images: NASA
The Atmosphere The auroras occur in the thermosphere and are caused by interactions between the Earth’s atmosphere and charged particles streaming from the Sun. • The mixture of gases known as air, protects life on Earth by absorbing ultraviolet radiation and reducing temperature extremes between day and night. • The atmosphere is not static. Interactions involving the amount of sunlight, the spin of the planet and tilt of the Earth’s axis cause ever changing atmospheric conditions. Weather occurs in the troposphere. Gaseous water molecules held together by intermolecular forces cause the formation of clouds.
Atmospheric Layers Meteor burning up Stratosphere Temperature is stable to 20 km, then increases due to absorption of UV by the thin layer of ozone. Mesosphere Temperature is constant in the lower mesosphere, but decreases steadily with height above 56 km. Thermosphere This layer extends as high as 1000 km. Temperature increases rapidly after about 88 km. Troposphere Air mixes vertically and horizontally. All weather occurs in this layer. Aurora, caused by collisions between protons and electrons from the Sun and oxygen and nitrogen atoms in the atmosphere. • The atmosphere consists of layers around the Earth, each one defined by the way temperature changes within its limits. • The layer boundaries are: • Tropopause • Stratopause • Mesopause • The outermost, the thermosphere, thins slowly, fading into space with no boundary.
Movement of Air Westerlies Hadley Ferrel Polar cell High cell cell Northeasterly trade winds Equator cell Hadley Southeasterly trade winds High Westerlies cell Ferrel Polar cell • The air of the atmosphere moves in response to heating from the Sun. • Circulation in the atmosphere transports warmth from equatorial areas to high latitudes, returning cooler air to the tropics. • The rotation of the Earth causes these movements to break up into three distinct air cells in each hemisphere. Image NASA
Air Cells In the tropics, wind blowing towards the equator as part of the Hadley cells is deflected (by the Corioliseffect) and forms the northeasterly and southeasterly trade winds. Air within the Hadley cells rises moist at the equator and subsides dry at the tropics. Rising mid-latitude air divides, flowing to the poles and the equator forming the Ferrel cells. These mid-latitudinal cells produce westerly winds. Ferrel Polar cell Hadley cell cell 60o N 30o N Equator 0o Image NASA
0o Air Cells The atmospheric circulation in each hemisphere consists of three cells (at polar, mid-latitude, and equatorial regions). These cells produce belts of prevailing winds around the world. Warm air rises at the equator and moves poleward through the upper troposphere before sinking at the edge of the tropics. At the poles, air cools and descends as a cold, dry high pressure area, moving away from the pole flowing towards the equator. 30o S 60o S Image NASA Equator
Coriolis Effect Air flowing towards, or away from, the equator follows a curved path that swings it to the right in the northern hemisphere and to the left in the southern hemisphere. This phenomenon, known as the Coriolis effect, is caused by the anticlockwise rotation of the Earth about its axis. • Energy from the Sun is distributed through a global system of atmospheric and ocean circulation that creates the Earth's climate. • Heated air moving towards the poles from the equator does not flow in a single uniform convection current. • Friction, drag, and momentum cause air close to the Earth's surface to be pulled in the direction of the Earth's rotation. Image: NASA
Coriolis Effect • The deflection of moving air is called the Coriolis effect and it is responsible for the direction of movement of large-scale weather systems in both hemispheres. • Air flows from high pressure to low pressure. • In the northern hemisphere, cyclonic (low pressure) systems rotate counterclockwise. • In the southern hemisphere, cyclonic systems spiral in a clockwise direction. • Cyclonic weather is usually dull, with cloud and persistent rain. Hurricane, Northern hemisphere Cyclone, Southern hemisphere All photos NASA
The Ocean Surface Photo: Wiki Commons, NOAA • Throughout the oceans, there is a constant circulation of water, both across the surface and at depth. • Surface circulation, much of which is in the form of circular gyres, is driven by winds. • The polar oceans comprise the Arctic Ocean in the northern hemisphere and the Southern Ocean in the south. They differ from other oceans in having vast amounts of ice, in various forms, floating in them. • This ice coverage has an important stabilizing effect on global climate, insulating large areas of the oceans from solar radiation in summer and preventing heat loss in winter. The Southern Ocean encircles Antarctica and is covered in ice for much of the year. Complex currents in the Southern Ocean produce rich upwelling zones that support abundant plankton and complex food webs. Satellite observations have shown the sea ice around the poles is melting earlier and more rapidly than first thought. The loss of ice dramatically reduces the albedo (reflectivity) of the polar regions.
Ocean Currents High salinity water cools and sinks in the North Atlantic. Atlantic waters are saltier and therefore more dense than those in the Pacific. Cold water circulates through the Atlantic penetrating the Indian and Pacific Oceans. Deep water returns to the surface in the Pacific and Indian oceans through upwelling. The polar oceans (the Arctic and Southern Oceans) are sources of cold dense bodies of water that drive the Earth’s deep water circulation. Atlantic Ocean Pacific Ocean Indian Ocean Warm shallow current Cold and deep high salinity current • The deep-water ocean currents (the thermohaline circulation) is driven by the cooling and sinking of water masses in polar and subpolar regions. • Cold water circulates through the Atlantic, penetrating the Indian and Pacific oceans, before returning as warm upper ocean currents to the South Atlantic. • Deep water currents move slowly and once a body of water sinks it may spend hundreds of years away from the surface.
Gyres North Atlantic Gyre South Pacific Gyre North Pacific Gyre Sargasso Sea Great Pacific Garbage Patch South Atlantic Gyre Indian Ocean Gyre • The movement of surface waters tends to form ocean-wide vortices. • At the center of these vortices, water currents are almost nonexistent and water tends to be stagnant. • The Sargasso Sea is a well known example.
Great Pacific Garbage Patch Midway Is. Midway Island lies near the center of the GPGP. Every tide brings in vast amounts of debris, from parts of old fishing nets to plastic bags and bottles. It is a poignant example of how even the most isolated places of Earth are affected by human activities. • As with all vortices, debris is swept towards the middle of the water currents. • The Great Pacific Garbage Patch is an accumulation of plastic and other debris in the middle of the North Pacific Gyre. • It spans an area of approximately 1.2 million km2. Photo: Duncan Wright Nearly two million Laysan albatrosses live on Midway. It is estimated all of them contain some quantity of plastic. This juvenile died after swallowing at least three bottle caps, some fishing line and a felt tip pen.