Chapter 2: The Planet Earth PDF

## Chapter Two: The Planet Earth ### Introduction The planet Earth is a dynamic part of the solar system, interacting with asteroids, meteorites, comets, and the moon. The origin of Earth and its solar system has been researched for hundreds of years. Scholars have developed various theories about...

## Chapter Two: The Planet Earth ### Introduction The planet Earth is a dynamic part of the solar system, interacting with asteroids, meteorites, comets, and the moon. The origin of Earth and its solar system has been researched for hundreds of years. Scholars have developed various theories about how the Earth evolved and changed over time. In this chapter, we will learn about the Earth’s origin, its position in the solar system, and its shape and size. ### Think #### Origin of the Planet Earth **Activity 2.1** (a) Research online for simulation videos or animations on the origin of the Earth. (b) Focus your search on the Big Bang theory, Nebula hypothesis, and Inter-stellar dust hypothesis, and create a summary of your findings. The Earth is the only known planet in the solar system that supports life. Its surface is comprised of land and water bodies. The evolution of the Earth can be traced through various assumptions, including both theories and hypotheses, which explain the origin of the universe. Scholars have developed several ideas, principles, and assumptions which aim to trace the origin of the universe from which Earth originated. These assumptions examine the various processes by which the universe, galaxies, stars, and planets were formed, and the changes that are still taking place over time. ### Origin of the Earth Some of the assumptions that explain the origin of the Earth include the Big Bang theory, Nebula hypothesis, Inter-stellar dust hypothesis, and the Creation theory. Various critiques have emerged against these theories and hypotheses, though they remain important for understanding the evolution of the universe and the planet Earth in particular. #### Nebular Hypothesis This hypothesis, proposed by Immanuel Kant in 1755, explains the origin of the Earth. It states that the solar system was formed from a cold, spinning cloud of gases called the solar nebular. This cloud resulted from uneven distribution of gases throughout the universe in the Milky Way Galaxy. As the gravitational pull condensed the gas towards the center, the speed of its rotation increased. This caused the cloud to flatten, and created an accretion disk. Matter continued to collect as the force of gravity toward the center increased. Eventually, the gas warmed from increasing pressure. As the mass further increased, also the gravity increased, and the temperature continued to rise. A ball of hot gas formed in the center of the accretion disk, creating a protostar, also known as the Sun. Finally, when enough gas gathered in the center of the protostar, the pressure generated enough heat to fuse the atoms to form a star. Outside the star, matter was forming into clumps of gas, dust and rocks, which created protoplanets that are believed to give rise to the planets. The theory was modified by Pierre Laplace in 1796. #### Big Bang Theory This theory, proposed by Lemaître Georges and Edwin Hubble in the 1920s, explains that about 15 billion years ago, a great explosion occurred. This explosion caused the expansion of the universe. At the time of this event, all matter and energy in space were contained in one point. The explosion pushed matter and energy outward expanding in all directions, forming a collection of dust, gas, and stars held together by gravitational attraction. Later, the sun, gas, and dust collided and aggregated into small grains, eventually forming larger bodies called planetesimals (very small planets). Some of these small planets reached diameters of several hundred kilometers, and later formed the current eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune) and their satellites. However, scientists and institutions such as NASA (National Aeronautics and Space Administration) are still investigating to find out if there is existence of other planets in the outer space. The critique of the theory is that it appears all galaxies emerged at the same time; therefore, they could potentially have at least the same age. However, this has not been the case. Currently, astronomers have found that while other galaxies are very old, there are many young galaxies around and far from Earth. #### Inter-Stellar Dust Hypothesis In 1943, a Russian scientist Otto Schmidt proposed the Inter-Stellar dust hypothesis. This theory explains the complex problems of the origin and characteristics of the solar system and the Earth. According to the Inter-Stellar dust hypothesis, the Sun, during its 'galactic revolution, captured the dark matter of the universe. The dark matter (Inter-Stellar dusts) of gaseous cloud and dust particles had their own angular momentum. The dark matter after being attracted by the Sun during its 'galactic revolution' started revolving around the primitive rotating Sun. The intense heat from the Sun dispersed the gaseous particles towards the margins of the disk. Collisions among dust particles started the process of aggregation and accretion around the bigger particles which became the essentials of the future planets. With the passage of time, these embryos captured more and more matter and grew in size to become asteroids. Furthermore, these asteroids grew in size due to continuous acceleration of nearby matter around them; thus, they became planets. The hypothesis has been criticized as the gravitational force of the primitive Sun was incapable of capturing dark matter scattered in the universe. The second critique is that some astrophysicists believe that meteorites and asteroids were formed from disintegration of planets. Thus, they reject the idea that planets were formed out of meteorites and asteroids. ### Activity 2.2 Research the creation theory from books and reliable online sources. Prepare points to oppose or support the theory in relation to other theories. ### Exercise 2.1 1. How do you relate the sun, moon, stars, and other objects you see in the sky to the origin of the Earth? 2. Using the theories you have identified regarding the Earth’s origin, complete the provided matrix. | Name of the theory | Key Assumptions | Critique | |---|---|---| | Big Bang Theory | | ||||| | Nebula Hypothesis | | ||||| | Inter-stellar Dust Hypothesis | | ||||| 3. Do you think that knowledge about the origin of the Earth has significance in your everyday life? Provide reasons to support your answer. ### Position of the Earth in the Solar System **Activity 2.3** Utilize materials readily available in your local area to design a model illustrating the solar system, displaying all the planets and their orbital paths. According to the origin of the universe, the solar system is found in one arm of the Milky Way galaxy. The Milky Way is a galaxy with a spiral arm structure and a central bar-shaped region composed of stars, gas, dust, and dark matter. The name "Milky Way" arises from its appearance as a hazy band of light stretching across the night sky. This band is composed of countless distant stars and other celestial objects. This band is most visible from Earth in areas with minimal light pollution. A galaxy is a vast and immense system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. These components are held in specific, organised structure that can take various forms, including spiral, elliptical, or irregular shapes. Galaxies come in a wide range of sizes, with some containing just a few million stars, while others, like the Milky Way, host hundreds of billions of stars. Additionally, galaxies can exist in isolation or be part of larger groups or clusters of galaxies. The universe is teeming with galaxies and they are the basic building blocks of the cosmic structure. They serve as focal points for astronomical study and are integral to our understanding of the larger cosmos. Each galaxy, in turn, can be home to its own planetary systems, which may include planets, moons, asteroids, and comets. The Milky Way is just one of billions of galaxies in the universe. It plays a fundamental role in our understanding of the cosmos and it is a subject of extensive study in the fields of astronomy and astrophysics. The solar system is composed of a set of different types of planets, moons, asteroids, comets, meteorites, interplanetary dusts and gases. Planets are arranged from the outer gas giants which consist of Jupiter, Saturn, Uranus, and Neptune to the rocky inner planets which comprises of Mercury, Venus, Earth and Mars. The inner planets are smaller, hotter, and solid than the outer planets which are large, cold, and gaseous in nature. The Earth is the third planet in position from the Sun. It is a unique and precious celestial body in the universe. It is the only known celestial body that supports life. Despite this, the Earth still faces numerous challenges, such as climate change, pollution, deforestation, loss of biodiversity, and overconsumption of natural resources, which are associated with unsustainable human exploitation of resources. Increasingly, the challenges are threatening life on the planet. ### Shape and Size of the Earth **Activity 2.4** In a dimly lit room, shine a flashlight towards a spherical object resting on a flat surface like a table. Make sure the flashlight is switched on and is casting a beam of light on the spherical object. Observe the shadow that appears on the wall. The Earth is the fifth largest planet in the solar system in terms of size and mass. Its shape is a flattened sphere known as an oblate spheroid (geoid). The flattening of the Earth is very slight as shown by the measurements of the North-south and East-west distances. The distance through the center from the North Pole to the South Pole is approximately 12,713 kilometers, whereas the distance through the center of the Earth at the Equator is approximately 12,757 kilometers. The circumference of the Earth at the equator is about 40,085 kilometers while the polar circumference is 39,955 kilometers. However, the Earth’s axis is not upright. It is tilted relative to the plane of its orbit. This axial tilting of the Earth refers to the angle between the Earth’s rotational axis and a perpendicular to the plane of its orbit around the Sun. The Earth’s axis of rotation is an imaginary line that runs from the North Pole to the South Pole. This tilting is approximately 23 1/2 degrees. The tilt of this axis is responsible for the changing seasons and variations in daylight hours throughout the year. It is significant in shaping the Earth’s climate, seasons, and overall environmental conditions. **Activity 2.5** (a) Use reliable online sources to search for videos or animations of the Earth's appearance. Study them and comment on the shape of the Earth and its horizon. (b) Relate your observations to the evidence that supports the shape of the Earth. The Earth has an oblate spheroid shape. There are several pieces of evidence to justify the spherical shape of the Earth. Such pieces of evidences include the following: (i) Sunrise and sunset The Sun rises and sets at different times in different places on the Earth. People in the East see the sun earlier than those in the West due the spinning of the Earth on its own axis from West to East. If the Earth was flat, the whole world would have sunrise and sunset at the same time. (ii) Circumnavigation of the Earth If you travel from a certain point on the Earth by going in a straight line around it, you will eventually come back to the point of origin. This concept was proved by the first navigator Ferdinand Magellan who sailed around the world from 1519 to 1522. Magellan in his voyage did not encounter any abrupt edge on earth’s surface over which he would fall. This journey around the earth is called circumnavigation of the Earth. (iii) Aerial photograph of the Earth Several vertical photographs taken from an airplane or images captured by artificial satellites from great heights show that the Earth is curved. (iv) Ship's visibility When watching an arriving ship from the coast, the visibility of the ship, which is far away, starts with the flag, then the mast, and eventually the whole ship is seen as it approaches the coast. When the ship moves away, it gradually disappears starting with the ship, then the mast, and finally the flag. If the Earth was flat, the whole ship would appear or disappear at once. (v) Lunar eclipse When light from the Sun is obstructed, a circular shadow is observable. For example, during the eclipse of the moon, the shadow of the Earth on the moon appears spherical . (vi) Earth’s curved horizon The Earth appears to have a curved horizon when viewed from a high cliff, a plane or a high building. The earth's curved horizon widens as the observer's altitude increases until it becomes circular. ### Exercise 2.2 1. Give evidence to justify that the Earth is not a flat surface. 2. How does the Earth’s shape affect the occurrence of day and night? ### Revision Exercise 2 1. Differentiate the following: (a) Inter-stellar dust hypothesis and Nebular hypothesis (b) Planet and Milky Way Galaxy 2. Match the item in Column A with their corresponding response in Column B. | Column A | Column B | |---|---| | (a) Evidence to prove that the shape of the Earth is a slightly flattened sphere | (i) Earth | | (b) The fifth largest planet in the solar system | (ii) Orbit | | (c) It generates heat and light that are essential for life | (iii) Sun | | (d) Jupiter, Saturn, Uranus, and Neptune | (iv) Circumnavigation | | (e) Mercury, Venus, Earth and Mars | (v) Solar eclipse | | | (vi) Gas giant planets | | | (vii) Rocky planets 3. In which ways does the Earth sustain life by considering the role of soil, water, sunlight, and various gases like oxygen, carbon dioxide, hydrogen and ozone in the process? 4. Planets are positioned in different locations in the solar system; they all revolve around the Sun. Give reasons why they do not experience collisions. 5. Assume the distance between the Earth and the Sun is reduced by half; explain what is likely to happen to living organisms on the Earth. 6. Explain with examples the consequences for living organisms, if the Earth were situated at a different position within the solar system.