The Earth System Connections among the great spheres

Transcription

1 The Earth System Connections among the great spheres Our Home Planet About 4.5 billion years old Only planet presently known to support life Has well-defined continents and ocean basins Very dynamic, both internally and externally A closed system! Earth As A Closed System Four Spheres Within Closed System Within this closed system are four major, interlinked components: Mass conserved within system (no gain or loss) Closed system: exchange of energy but negligible exchange of mass with surroundings Geosphere Hydrosphere Atmosphere Biosphere Energy and matter are exchanged between these components. In this course, our focus will be on the biosphere. So while we re thinking about it 1

2 Why can Earth sustain life? Not too close or far from Sun, thus preventing life from freezing or frying Earth s Four Spheres Large enough to hold atmosphere Abundance of water Temperature range to allow water to exist in liquid (very important) as well as gaseous, and solid forms. The interaction of the four components or spheres of the Earth system. The origin of life is a separate issue, which we will discuss later. Geosphere Geosphere: The solid, inorganic Earth, including Earth s surface and layers of its interior. The Earth is composed of nested shells that are classified according to their chemical and mechanical characteristics. Earth s Layers: Composition and Mechanical Characteristics Primarily silica plus light metallic elements Primarily silica plus iron and magnesium Primarily iron and nickel Composition crust mantle core Mechanical Characteristics lithosphere asthenosphere mesosphere outer core inner core brittle solid solid (but nearly liquid) solid liquid solid 2

3 Geosphere: Chemical and Mechanical Characteristics Combined Some important roles of the geosphere: 1. Contributor of particulate matter (e.g. volcanic ash) to atmosphere. 2. Ultimate contributor of salts to the ocean (due to ions being released from weathered rock). 3. Ultimate source of nutrients for all living things. 4. Important contributor of atmospheric gases (from volcanoes) Note: Lithosphere contains both crust and uppermost (brittle) layer of mantle 5. Movement of plates produces barriers that aid in the isolation of population of organisms (and therefore influences evolution). The Dynamic Geosphere Processes that occur beneath Earth s surface are manifest in earthquakes and volcanism. These phenomena are linked to the movement of tectonic plates that, in turn, is driven by internal Earth processes. Hydrosphere Hydrosphere:The hydrosphere is composed of all of the water in the Earth system, including water in the oceans, rivers, lakes, air, and below Earth s surface. 97 percent of the earth's water is in the oceans. The remaining 3 percent is fresh water (mostly in ice sheets, but also in the air as vapour, and below Earth s surface as groundwater). Earthquakes Volcanoes Plate Boundaries Surface temperatures of oceans (blue= coldest red= warmest) The presence of liquid surface water makes our planet unique. 3

4 Hydrosphere Some important roles of the hydrosphere: 1. Moderates climate 2. Transfers heat 3. Organisms need water to transport nutrients and waste 4. Water is essential in many of Earth s processes, from mineral formation to the weathering and erosion of rock. Atmosphere Atmosphere: The atmosphere is the body of gases that surrounds our planet. Most of our atmosphere is located close to the earth's surface where it is most dense. The air of our planet is 79% nitrogen and just under 21% oxygen; the small amount remaining is composed of carbon dioxide and other gases. Also has a layered structure (but we won t get into this right now) Biosphere Some important roles of the atmosphere: 1. Contains the gases that living things need for survival (e.g., carbon dioxide for photosynthesis, and oxygen for aerobic respiration). 2. Transfers heat. 3. Ozone in stratosphere protects living things from excess ultraviolet radiation. 4. Plays a part in weathering and erosion. Biosphere: The sphere that includes all living organisms. Plants, animals, and microbes are all part of the biosphere. It also includes organic matter not yet decomposed. Most of Earth s life is found from about 3 metres below the ground to 30 meters above it and in the top 200 metres of the oceans and seas. But life can thrive in the most unlikely places, from hot springs to ice caps. 4

5 Some important roles of the biosphere: 1. Aids in weathering (e.g. formation of acids in soil). 2. An important sink for certain elements (especially carbon). 3. Mediates the formation of some minerals. 4. Photosynthesis maintains the oxygen content of the atmosphere. A Recent Addition to Biosphere: Human Activity The presence of humans and the extent of human influence can be appreciated by looking at satellite photos. Even at night, evidence of human activity can be seen. White dots: major centres of human population Yellow patches: fires from slash-and-burn farming Red patches: natural gas burning in major oil fields Interconnectedness of Spheres To appreciate how strongly interconnected the Earth s spheres really are, we need only to think about what happens to substances within the system. Other Circumstances: Earth s Spin and Tilt Earth is not just a static lump of rock! For example, the carbon cycle. Note that at any given point in time, carbon occurs in all of the great spheres. As it spins on its tilted axis, it different areas of Earth are exposed to different amounts/intensities of the Sun s energy. This gives us seasons. 5

6 Example 1 Considering Interactions Between the Spheres Example 2 Identify some interactions that are represented in this picture What about this picture? Example 3 Small-scale example: A forest fire or this one? 6

7 Interactions Between Spheres: Cause and Effect Initial Conditions Geosphere: The ground could have been very permeable, preventing moisture from being retained in the upper part of the soil profile. Relevance to Geosphere 1. Heat from the fire causes rocks to crack (therefore enhancing weathering). 2. Soil erosion is also enhanced by the removal of vegetation. Hydrosphere: The area could have been prone to fire due to lack of precipitation. Atmosphere: The fire could have started due to a lightning strike. Biosphere: Dead wood, leaves and needles may have enhanced the ability of the fire to start and spread. 3. Ash particles from the fire alter the chemistry of the soil. Relevance to Atmosphere 1. Smoke and ash particles are carried by wind to other areas. Relevance to Hydrosphere 1. Heat from the fire further removes moisture from the air, soil, and vegetation through the process of evaporation. 2. Increased siltation of streams due to enhanced erosion (particles are then deposited as sediment). 2. Increased precipitation elsewhere is enhanced due to the ash particles acting as nucleation centres for water droplets. 3. Gaseous pollutants such as carbon dioxide (CO 2 ) are produced during the burning of the vegetation and carried into the air by the wind. 7

8 Relevance to Biosphere 1. Immediate destruction of habitat in burn area. Relevance to Biosphere 4. On the positive side, nutrients released from ash from the fire can, on the long term, benefit future plant communities. 2. Smoke in the air may have coats the lungs of animals, including people, and affects their ability to breathe. 3. Ash particles in water clogs the gills of fish and other aquatic organisms. 5. Also, seeds of some plants may require that their outer shells be burned before they can germinate (so the forest fire benefits these plants). Global Effects These types of interactions not only apply to local scenarios, but also influence changes on global scale. Examples of events that may have something to do with interactions between components of the Earth system: 1. Initiation of ice ages 2. Mass extinctions 3. Global climate change 4. El Nino events. We will look at some of these things in detail as the course progresses. Just how integrated is the Earth System? James Lovelock (1979) introduced a somewhat extreme concept called the Gaia Hypothesis. Named after Gaia, Greek goddess of Earth ( Mother Earth ) An interesting piece of trivia: Gaia was gentle, feminine and nurturing, but also ruthlessly cruel to any who crossed her. Lovelock claims that life, or the biosphere, regulates or maintains the climate and the atmospheric composition at an optimum for itself " 8

9 Is Earth Alive? The Gaia concept views Earth as a superorganism. Inherent in this explanation is the idea that biosphere, the atmosphere, the lithosphere and the hydrosphere are in some kind of balance - that they maintain a homeostatic condition. This also implies that Earth is somehow aware of the adjustments needed in its system to maintain a state of balance that Earth is a living, breathing, and thinking, entity. Gaia Hypothesis Put another way, we might view Earth s processes as being analogous to how physiological processes within the human body ensure that temperature, blood ph, electrochemistry, etc. are kept in balance for our survival. Few scientists accept the concept of Earth as a sentient entity. However, this idea has greatly influenced the way scientists think about how Earth behaves, in that it emphasized that every change that occurs in one part of the Earth system has the potential to affect all others. The Biosphere and Gaia The Gaia Hypothesis is particularly relevant in today s world- we are getting increasingly worried about how our activities are affecting the Earth. The Bottom Line Also, to have any hope in realistically reconstructing events in the past, we must be mindful of the intricate interconnections between Earth s components today (uniformitarianism) Everything that happens in the biosphere is dependent on what is happening in the geosphere, hydrosphere, and atmosphere. After all, how can we expect to fix something if we don t know how it works? 9

10 END OF LECTURE 10