LESSON-2.pdf

SCIENCE 3: EARTH SCIENCE LESSON 2 PLANET EARTH & ITS SYSTEMS ORIGIN OF THE PLANET EARTH Our story begins about 13.7 billion years ago, with the Big Bang, an incomprehensibly large explosion tha...

SCIENCE 3: EARTH SCIENCE LESSON 2 PLANET EARTH & ITS SYSTEMS ORIGIN OF THE PLANET EARTH Our story begins about 13.7 billion years ago, with the Big Bang, an incomprehensibly large explosion that sent all matter of the universe flying outward at incredible speeds. In time, the debris from this explosion, which was almost entirely hydrogen and helium, began to cool and condense into the first stars and galaxies. It was in one of these galaxies, the Milky Way, that our solar system and planet Earth took form. Earth is one of eight planets that, along with more than 160 moons and numerous smaller bodies, revolve around the Sun. The orderly nature of our solar system leads most researchers to conclude that Earth and the other planets formed at essentially the same time and from the same primordial material as the Sun. The nebular theory proposes that the bodies of our solar system evolved from an enormous rotating cloud called the solar nebula. Earth is also often called as the “Blue Marble” because of it looks like a blue globe encircled by swirling white clouds as seen from the outer space. As of today, Earth is the only planet in the Solar System that is habitable or where living things can exist although scientists are now looking at exoplanets that are potentially habitable. Are you familiar with the story of Goldilocks and the three bears? Scientists coined the term Goldilocks zone (habitable or life zone) for the regions in the space where a planet is just in the right distance from its home star (usually a low-mass star) so that its surface is neither too hot nor too cold. The term Goldilocks is related to the story of “Goldilocks and the Three Bears.” It is because of how a little girl named Goldilocks, who was lost in the woods and entered the house of the three bears, liked everything that is just right. She chose the porridge that is not too hot or too cold, the bed that is not too hard or too soft, and so on. Just like Goldilocks’ choices, our planet – Earth has factors necessary for life in just the right amount. Earth is so terrific that it is the only planet known in the Solar System that can support life but the question is, “What makes Earth unique among other planets?” and “What are the factors to consider a habitable planet?” Let us learn more through the following activities. Factors that Makes the Planet Habitable The right amount of the following factors makes the planet Habitable like Earth. 1. Temperature - Influences how quickly atoms & molecules move 2. Water - Dissolves & transports chemicals within and to and from a cell 3. Atmosphere - Traps heat, shields the surface from harmful radiation, and provides chemicals needed for life, such as nitrogen and carbon dioxide. 4. Energy - Organisms use light or chemical energy to run their life processes. 5. Nutrients - Used to build and maintain an organism’s body. 6. Magnetic Field - a planet requires a rapidly rotating magnetic field to protect it from flares from nearby stars and from harmful radiation HYDROSPHERE The hydrosphere is a dynamic mass of water that is continually on the move, evaporating from the oceans to the atmosphere, precipitating to the land, and running back to the ocean again.  The global ocean is certainly the most prominent feature of the hydrosphere, blanketing nearly 71 percent of Earth’s surface to an average depth of about 3800 meters (12,500 feet). It accounts for about 97 percent of Earth’s water. However, the hydrosphere also includes the freshwater found underground and in streams, lakes, and glaciers. Moreover, water is an important component of all living things. ATMOSPHERE Earth is surrounded by a life-giving gaseous envelope called the atmosphere. Despite its modest dimensions, this thin blanket of air is nevertheless an integral part of the planet. It not only provides the air that we breathe but also protects us from the Sun’s dangerous ultraviolet radiation. The energy exchanges that continually occur between the atmosphere and Earth’s surface and between the atmosphere and space produce the effects we call weather and climate. Climate has a strong influence on the nature and intensity of Earth’s surface processes. When climate changes, these processes respond. Weather and Climate Weather is a term that refers to the state of the atmosphere at a given time and place. Whereas changes in the weather are continuous and sometimes seemingly erratic, it is nevertheless possible to arrive at a generalization of these variations. Climate is often defined simply as “average weather,” but this is an inadequate definition. To more accurately portray the character of an area, variations and extremes must also be included, as well as the probabilities that such departures will take place. Major Components 1. Carbon dioxide- Carbon dioxide is of great interest to meteorologists because it is an efficient absorber of energy emitted by Earth and thus influences the heating of the atmosphere. 2. Variable components- Air includes many gases and particles whose quantities vary significantly from time to time and place to place. Important examples include water vapor, dust particles, and ozone a. Water vapour- The amount of water vapor in the air varies considerably, from practically none at all up to about 4 percent by volume. b. Aerosols- tiny solid and liquid particles. Its importance includes; act as surfaces on which water vapor can condense and absorb, reflect, and scatter incoming solar radiation. c. Ozone- It is a form of oxygen that combines three oxygen atoms into each molecule (O3).  Vertical Structure of the Atmosphere 1. Troposphere - The lowermost layer in which we live, where temperature decreases with an increase in altitude. The term literally means the region where air “turns over,” a reference to the appreciable vertical mixing of air in this lowermost zone. 2. Stratosphere- where the temperature remains constant to a height of about 20 kilometers (12 miles) and then begins a gradual increase that continues until the stratopause, at a height of nearly 50 kilometers (30 miles) above Earth’s surface. 3. Mesosphere- where the temperatures again decrease with height until, at the mesopause— approximately 80 kilometers (50 miles) above the surface, the temperature approaches 2908C (21308F). 4. Thermosphere- The fourth layer extends outward from the mesopause and has no well-defined upper limit. It is the thermosphere, a layer that contains only a tiny fraction of the atmosphere’s mass. In the extremely rarefied air of this outermost layer, temperatures again increase, due to the absorption of very short-wave, high-energy solar radiation by atoms of oxygen and nitrogen. Temperatures rise to extremely high values of more than 1000°C (1800°F) in the thermosphere. But such temperatures are not comparable to those experienced near Earth’s surface. BIOSPHERE The biosphere includes all life on Earth. Ocean life is concentrated in the sunlit surface waters of the sea. Most life on land is also concentrated near the surface, with tree roots and burrowing animals reaching a few meters underground and flying insects and birds reaching a kilometer or so above the surface. A surprising variety of life-forms are also adapted to extreme environments. For example, on the ocean floor, where pressures are extreme and no light penetrates, there are places where vents spew hot, mineral-rich fluids that support communities of exotic lifeforms. On land, some bacteria thrive in rocks as deep as 4 kilometers (2.5 miles) and in boiling hot springs. Moreover, air currents can carry microorganisms many kilometers into the atmosphere. But even when we consider these extremes, life still must be thought of as being confined to a narrow band very near Earth’s surface. Plants and animals depend on the physical environment for the basics of life. However, organisms do more than just respond to their physical environment. Through countless interactions, life-forms help maintain and alter their physical environment. Without life, the makeup and nature of the geosphere, hydrosphere, and atmosphere would be very different than they are. GEOSPHERE The geosphere extends from the surface to the center of the planet, a depth of 6400 kilometers [4000 miles], making it by far the largest of Earth’s four spheres. Soil, the thin veneer of material at Earth’s surface that supports the growth of plants, may be thought of as part of all four spheres. The solid portion is a mixture of weathered rock debris (geosphere) and organic matter from decayed plant and animal life (biosphere). The decomposed and disintegrated rock debris is the product of weathering processes that require air (atmosphere) and water (hydrosphere). Air and water also occupy the open spaces between the solid particles. EARTH’S INTERNAL STRUCTURE 1. EARTH’S CRUST- Earth’s relatively thin, rocky outer skin. a. Oceanic crust- is roughly 7 kilometers (5 miles) thick and composed of the dark igneous rock basalt. b. Continental crust- averages about 35 kilometers (22 miles) thick but may exceed 70 kilometers (40 miles) in some mountainous regions, such as the Rockies and Himalayas. 2. EARTH’S MANTLE- More than 82 percent of Earth’s volume is contained in the mantle, a solid, rocky shell that extends to a depth of nearly 2900 kilometers (1800 miles). Perioditite is the dominant rock type in the upper mantle. a. Lithosphere- (“sphere of rock”) consists of the entire crust and uppermost mantle and forms Earth’s relatively cool, rigid outer shell. Averaging about 100 kilometers (60 miles) in thickness, the lithosphere is more than 250 kilometers (150 miles) thick below the oldest portions of the continents b. Asthenosphere- a soft comparatively weak layer lies beneath the lithosphere layer to a depth of about 350 kilometers (220 miles). The top portion of the asthenosphere has a temperature/pressure regime that results in a small amount of melting. c. Lower Mantle- From a depth of 660 kilometers (410 miles) to the top of the core. At a depth of 2900 kilometers (1800 miles) the rocks within the lower mantle are very hot and capable of very gradual flow.  3. EARTH’S CORE - The composition of the core is thought to be an iron–nickel alloy with minor amounts of oxygen, silicon, and sulfur—elements that readily form compounds with iron. a. Outer core- is a liquid layer 2260 kilometers (about 1400 miles) thick. It is the movement of metallic iron within this zone that generates Earth’s magnetic field. b. Inner core - is a sphere that has a radius of 1216 kilometers (754 miles). Despite its higher temperature, the iron in the inner core is solid due to the immense pressures that exist in the center of the planet. CONTINENTAL DRIFT AND PLATE TECTONICS During the past several decades, a great deal has been learned about the workings of our dynamic planet. This period has seen an unequaled revolution in our understanding of Earth. The revolution began in the early part of the twentieth century with the radical proposal of continental drift—the idea that the continents move about the face of the planet. This proposal contradicted the established view that the continents and ocean basins are permanent and stationary features on the face of Earth. For that reason, the notion of drifting continents was received with great skepticism and even ridicule. More than 50 years passed before enough data were gathered to transform this controversial hypothesis into a sound theory that wove together the basic processes known to operate on Earth. The theory that finally emerged, called plate tectonics, provided geologists with the first comprehensive model of Earth’s internal workings. According to the theory of plate tectonics, Earth’s rigid outer shell (the lithosphere) is broken into numerous slabs called lithospheric plates, which are in continual motion. More than a dozen plates exist. The largest is the Pacific plate, covering much of the Pacific Ocean basin. Notice that several of the large lithospheric plates include an entire continent plus a large area of the seafloor. Note also that none of the plates are defined entirely by the margins of a continent. Plate Motion Driven by the unequal distribution of heat within our planet, lithospheric plates move relative to each other at a very slow but continuous rate that averages about 1 centimeters (2 inches) per year—about as fast as your fingernails grow. Because plates move as coherent units relative to all other plates, they interact along their margins. Convergent boundary- are located wher two plates move towards each other, one of the plates plunges beneath the other and descends into the mantle. The lithospheric plates that sink into the mantle are those that are capped with relatively dense oceanic crust. Divergent boundaries- are located where 2 plates moves away from each other. Here the fractures created as the plates separate are filled with molten rock that wells up from the mantle. Transform fault boundaries- are plates that do not push together or pull apart. Instead, they slide past one another, so that seafloor is neither created nor destroyed. California’s San Andreas Fault is a well-known example.