Earth Science 11 Name: Block: Activity 1-2: Origin of the Earth Read the following passage, and then answer the questions at the end: Where Earth Science Begins: The Solar System Where shall the study of earth science begin land, oceans, atmosphere, or sky? A good choice seems to be the origin of the planet Earth. But Earth is only one member of a whole family of planets circling the sun. So begin with the origin of the whole family, which is called the solar system. Many hypotheses explanations that try to fit known facts have been proposed for the origin of the solar system. Every hypothesis has to consider these facts: 1 All planets revolve around the sun in the same direction. 2 The paths, or orbits, of the planets around the sun are all nearly circular. 3 The orbits are all in nearly the same flat surface or plane. 4 The sun turns (rotates) on its axis in almost the same plane as the planets, and in the same direction as the planets revolve. 5 Most of the moons revolve around their planets in the same direction as the planets revolve around the sun. This artist s conception of the solar system illustrates the elliptical orbits of the planets revolving around the sun. Notice the asteroid belt which is located between the orbits of Mars and Jupiter. The hypothesis that many astronomers favor now because it best fits the facts listed above is called the protoplanet hypothesis. It was first proposed about 1944 by a German astronomer, von Weizsacker, and modified by an American astronomer, Kuiper, in 1950.
According to the protoplanet hypothesis a great cloud of gas and dust was gradually transformed into the planets and natural satellites which make up the solar system. The Protoplanet Hypothesis The protoplanet hypothesis begins about 5 x 10 9 years ago with a great cloud of gas and dust rotating slowly in space. The cloud is at least 10 x 10 9 km in diameter. As time passes, the cloud shrinks under the pull of its own gravitation or is made to collapse by the explosion of a passing star. Most of the cloud s material gathers around its centre. Its shrinking makes it rotate faster, like a spinning whirlpool. The compression of its material makes its interior so hot that hydrogen fusion begins and the core of the cloud blazes into a newborn sun. About 10 percent of the material in the cloud forms a great plate-like disk surrounding the sun far into space. Friction within the disk causes most of its mass to collect in a number of huge whirlpools or eddies. These eddies shrink into more compact masses called protoplanets and later form planets and moons. Some uncollected material still remains as comets, meteorites, and asteroids. Origin of the Oceans Scientists now agree that when Earth first formed, it had neither oceans nor atmosphere. But as the protoplanet Earth changed to the planet Earth, it grew hotter. There were three sources of heat: compression, radioactive materials, and bombardment by showers of meteorites. Radioactive minerals are natural substances that give off energy, much of which becomes heat. Meteorites produce heat both by friction and by impact. When Earth became hot enough, volcanoes erupted, bringing hot lava and hot gases to the surface. The gases contained vast amounts of steam, which condensed into water that slowly accumulated as oceans. But how did the oceans get their dissolved minerals? It was once thought that the minerals now found in ocean waters were deposited by rivers over hundreds of millions of years. But most scientists now think that as volcanic rains fell onto the then hot molten rock of Earth s surface, mineral matter dissolved to make the oceans salty.
Scientists believe that the protoplanet Earth (a) had no oceans or atmosphere. As the intense heat of Earth s interior built up, volcanic eruptions began to occur (b). Repeated huge eruptions produced volumes of volcanic gases. The steam in these gases condensed upon reaching the surface (c) to form Earth s oceans. Origin of the Atmosphere The atmosphere that surrounds Earth today includes about 78 percent free nitrogen and 21 percent free oxygen. Free means these gases are not combined with other elements. The remaining 1 percent is mostly other gases, such as argon, carbon dioxide, and helium. (Water vapour is in the atmosphere too, but it varies in amount with weather and climate.) This present mixture is very different from what scientists believe Earth s original atmosphere must have been. They believe that the original atmosphere came from volcanoes and was like the mixture of gases that now erupts from volcanoes. This mixture usually is over 50 percent water vapour with large amounts of carbon dioxide and sulfur gases. However, the mixture contains no free oxygen! Almost all forms of life on Earth need free oxygen. Where, then, did it come from? Scientists think the atmosphere s first free oxygen came from the breakup of water molecules by sunlight in the upper atmosphere. Then as simple green plants came into existence, they added more free oxygen to the atmosphere by photosynthesis. In this process, green plants manufacture sugars and starches from carbon dioxide and water in the presence of sunlight. But more than half of the oxygen in the carbon dioxide and water is left over. This excess is released into the atmosphere as free oxygen. Structure of the Solid Earth Geologists today have a fairly clear picture of Earth s structure from its surface to its very centre. Since the centre is nearly 6400 km from the surface, most of this picture of Earth is obviously based on indirect evidence. For now, look at the Earth model that geologists describe. It has a spherical inner core 2800 km in diameter, made of solid iron and nickel. Surrounding the inner core is an outer core about 2100 km thick made of liquid iron and nickel. Then comes a 2850 km thick layer of heavy rocks rich in compounds of iron, magnesium, and silicon. This layer is called the mantle. It reaches almost to Earth s surface. The mantle is covered by a layer of lighter rocks called the crust. The curst ranges in thickness form about 10 km below the ocean basins to about 65 km below the continents. Mines and wells go deep into the crust, but none have reached the mantle. Was Earth layered like this when it formed more than four hundred million years ago? Probably not! If we believe the protoplanet hypothesis, the surface of Earth looked much like the moon does today. Below its surface, Earth was probably composed of the same kind of rock all the way to its centre.
How then did Earth develop its layers of core, mantle, and crust? Many geologists think that as the temperature of the newly formed Earth increased, large quantities of iron and nickel in its rock melted. Great streams of these hot, heavy liquids flowed toward Earth s centre. On their way down they melted lighter rock materials and forced them up to the surface. At the surface the light rock became solid and formed Earth s crust. The mantle formed between the crust and the core. How the Continents Formed One hypothesis suggests that when the melted iron and nickel sank into Earth s core, it forced out enough light rock to form an immense single continent. Another suggestion is that the continents were formed by great lava flows form erupting volcanoes over hundreds of millions of years. In either case, today s continents are quite different from those that first formed on Earth s surface. In the hundreds of millions of years following their origin, the continents have undergone many changes. Source: Namowitz, Samuel N., and Nancy E. Spaulding. "Introduction to Earth Science." Earth Science. Canadian ed. Lexington, MA: D.C. Heath Canada, 1987. 6-10. Print. Questions 1. Why do scientists think that all the planets formed at about the same time? List at least three reasons. 2. Briefly describe the protoplanet hypothesis. 3. What was the planet Earth like before the oceans were formed?
4. Where did the water that formed the oceans come from? 5. How did the new oceans get salty? 6. What was the original atmosphere of the Earth like? What was it made of? 7. Where did the gases that formed the original atmosphere come from? 8. What is Earth s present atmosphere made of? 9. Which process is responsible for introducing oxygen gas into the atmosphere?
10. Complete the following table: Layer Thickness of Layer Composition of Layer crust mantle outer core inner core 11. Label the layers of Earth s interior in the following diagram and colour code them: 12. Describe the process which caused the layers of the Earth to form. 13. As the layers of the Earth formed, where did the least dense materials accumulate? What feature of present-day Earth was formed from these materials?
Review of Sections 1-1 and 1-2 1. Match each statement with the appropriate term: Made of solid iron. All water at or near Earth s surface. An explanation of known facts. The study of the seas. Allows matter to enter or exit. Made of molten iron and nickel. The study of the atmosphere. Movement of energy into and out of Earth system. Continuous circulation of water through the hydrosphere. Where all living things are located. Made of iron and magnesium silicates. Made of lighter aluminum silicates. The (mostly solid) Earth; all rock material. The study of Earth s surface and interior. Envelope of gases surrounding Earth. Allows energy to enter or exit, but not matter. Involves the movement of atoms between Earth s spheres. The study of the universe. Manufacture of sugars by plants. A) oceanography B) biosphere C) carbon cycle D) closed system E) crust F) meteorology G) mantle H) inner core I) atmosphere J) astronomy K) hypothesis L) geology M) hydrosphere N) photosynthesis O) open system P) outer core Q) water cycle R) geosphere S) energy cycle 2. Write the name of the earth scientist who studies the topic. Choose from geologist, meteorologist, oceanographer, or astronomer. a) Observes and predicts the appearance of comets. b) Predicts the weather. c) Explores for metal ores. d) Describes the paths of icebergs along shipping lanes. e) Predicts the paths of tsunamis. f) Studies solar radiation. g) Studies air pollution. h) Explores for geothermal power. i) Attempts to forecast earthquakes.
j) Studies marine plants and animals. k) Plans water supplies for cities and towns. l) Hypothesizes about distant galaxies. m) Maps ocean currents. n) Studies volcanic eruptions. o) Measures the strength of hurricanes. p) Studies the origin of the solar system. q) Measures ocean depths. r) Uses satellites to locate storms at sea. s) Studies how the ocean affects climate. t) Studies meteorites to determine if life exists elsewhere. u) Determines the locations sources of oil.