Cosmologists have postulated two endings to the Universe ...



Booklet 3Physical GeographyEvolution of the UniverseAbout 11 to 15 billion years ago all of the matter and energy in the Universe was concentrated into an area the size of an atom. At this moment, matter, energy, space and time did not exist. Then suddenly, the Universe began to expand at an incredible rate and matter, energy, space and time came into being (the Big Bang). As the Universe expanded, matter began to coalesce into gas clouds, and then stars and planets. Our solar system formed about 5 billion years ago when the Universe was about 65% of its present size (Figure 5a-2). Today, the Universe continues to expand.Figure 5a-1: Hubble Space Telescope view of a distant cluster of galaxies near the beginning of time. (Source: AURA/STScI).Figure 5a-2: Our solar system began forming about 5 billion years ago as gas clouds coalesce into planets and a star. Today, the solar system contains nine commonly recognized planets and the Sun. (Source: NASA).?BIG BANG THEORY The Big Bang Theory is the leading explanation about how the universe began. At its simplest, it says the universe as we know it started with a small singularity, then inflated over the next 13.8 billion years to the cosmos that we know today.Because current instruments don't allow astronomers to peer back at the universe's birth, much of what we understand about the Big Bang Theory comes from mathematical formulas and models. Astronomers can, however, see the "echo" of the expansion through a phenomenon known as the?cosmic microwave background.While the majority of the astronomical community accepts the theory, there are some theorists who have?alternative explanations besides the Big Bang?— such as eternal inflation or an oscillating universe.The phrase "Big Bang Theory" has been popular among astrophysicists for decades, but it hit the mainstream in 2007 when a comedy show with the same name premiered on CBS. The show follows the home and academic life of several researchers (including an astrophysicist).?GROUP 1Why do Most Scientists Accept the Big Bang Theory?The acceptance of this theory by the scientific community is based on a number of observations. These observations confirm specific predictions of the Big Bang theory. In a previous section, we learned that scientists test their theories through deduction and falsification. Predictions associated with the Big Bang theory that have been tested by this process are:If the Big Bang did occur, all of the objects within the Universe should be moving away from each other. In 1929, Edwin Hubble documented that the galaxies in our Universe are indeed moving away from each other.The Big Bang should have left an "afterglow" from the explosion. In the 1960s, scientists discovered the existence of cosmic background radiation, the so-called "afterglow" after the Big Bang explosion. Our most accurate measurements of this cosmic radiation came in November 1989, by the Cosmic Background Explorer (COBE) satellite. The measurements from this satellite tested an important prediction of the Big Bang This prediction suggests that the initial explosion that gave birth to the Universe should have created radiation with a spectrum that follows a blackbody curve. The COBE measurements indicated that the spectrum of the cosmic radiation varied from a blackbody curve by only 1%. This level of error is considered insignificant.If the Universe began with a Big Bang, extreme temperatures should have caused 25 percent of the mass of the Universe to become helium. This is exactly what is observed.Matter in the Universe should be distributed homogeneously. Astronomical observations from the Hubble Space Telescope do indicate that matter in the Universe generally has a homogeneous distribution.?How will the Universe End? (Big Crunch ) GROUP 2Cosmologists have postulated two endings to the Universe. If the Universe is infinite or has no edge, it should continue to expand forever. A Universe that is finite or closed is theorized to collapse when expansion stops because of gravity. The collapse of the Universe ends when all matter and energy is compressed into the high energy, high-density state from which it began. This scenario is of course called the Big Crunch. Some theorists have suggested that the Big Crunch will produce a new Big Bang and the process of an expanding Universe will begin again. This idea is called the oscillating Universe theory. Big CrunchThe Big Crunch is one of the scenarios predicted by scientists in which the Universe may end. Just like many others, it is based on Einstein’s Theory of General Relativity. That is, if the Big Bang describes how the Universe most possibly began, the Big Crunch describes how it will end as a consequence of that beginning.It tells us that the Universe’s expansion, which is due to the Big Bang, will not continue forever. Instead, at a certain point in time, it will stop expanding and collapse into itself, pulling everything with it until it eventually turns into the biggest black hole ever. Well, we all know how everything is squeezed when in that hole. Hence the name Big Crunch.For scientists to predict with certainty the possibility of a?Big Crunch, they will have to determine certain properties of the Universe. One of them is its density. It is believed that if the density is larger than a certain value, known as the critical density, an eventual collapse is highly possible.You see, initially, scientists believed that there were only two factors that greatly influenced this expansion: the gravitational force of attraction between all the galaxies (which is proportional to the density) and their outward momentum due to the Big Bang.Now, just like any body that goes against gravity, e.g. when you throw something up, that body will eventually give in and come back down for as long as there is no other force pushing it up.Thus, that the gravitational forces will win in the end, once seemed like a logical prediction. But that was until scientists discovered that the Universe was actually increasing its rate of expansion at regions farthest from us.To explain this phenomena, scientists had to assume the presence of an unknown entity, which they dubbed ‘dark energy’. It is widely believed that this entity is pushing all galaxies farther apart. With dark energy, and what little is known about it, in the picture, there seems to be little room for the possibility of a Big Crunch.Oscillating Universe Theory GROUP 3The Oscillating Universe Theory is a cosmological model that combines both the Big Bang and the Big Crunch as part of a cyclical event. That is, if this theory holds true, then the Universe in which we live in exists between a Big Bang and a Big Crunch.In other words, our universe can be the first of a possible series of universes or it can be the nth universe in the series.As we know, in the Big Bang Theory, the Universe is believed to be expanding from a very hot, very dense, and very small entity. In fact, if we extrapolate back to the moment of the Big Bang, we are able to reach a point of singularity characterized by infinitely high energy and density, as well as zero volume.This description would only mean one thing – all the laws of physics will be thrown out of the window. This is understandably unacceptable to physicists. To make matters worse, some cosmologists even believe that the Universe will eventually reach a maximum point of expansion and that once this happens, it will then collapse into itself.This will essentially lead to the same conditions as when we extrapolate back to the moment of the Big Bang. To remedy this dilemma, some scientists are proposing that perhaps the Universe will not reach the point of singularity after all.Instead, because of repulsive forces brought about by quantum effects of gravity, the Universe will bounce back to an expanding one. An expansion (Big Bang) following a collapse (Big Crunch) such as this is aptly called a Big Bounce. The bounce marks the end of the previous universe and the beginning of the next.The probability of a Big Bounce, or even a Big Crunch for that matter, is however becoming negligible. The most recent measurements of the CMBR or cosmic microwave background radiation shows that the Universe will continue on expanding and will most likely end in what is known as a Big Freeze or Heat Death.CMBR readings are currently being gathered by a very accurate measuring device known as the WMAP or Wilkinson Microwave Anisotropy Probe. It is the same device that has measured with sharp precision the age of our universe. It is therefore highly unlikely that future findings will deviate largely from what has been discovered regarding the Universe’s expansion now.There is however one mysterious entity whose deeper understanding of may change the possibilities. This entity, known as dark energy, is believed to be responsible for pushing the galaxies farther apart and subsequently the universe’s accelerated expansion. Unless its actual properties are very dissimilar from what it is showing now, we may have to shelve the Oscillating Universe Theory.?Early History of the Earth -GROUP 4Scientists believe the Earth began its life about 4.6 billion years ago. The Earth formed as cosmic dust lumped together to form larger and larger particles until 150 million years had passed. At about 4.4 billion years, the young Earth had a mass similar to the mass it has today. The continents probably began forming about 4.2 billion years ago as the Earth continued to cool. The cooling also resulted in the release of gases from the lithosphere, much of which formed the Earth's early atmosphere. Most of the Earth's early atmosphere was created in the first one million years after solidification (4.4 billion years ago). Carbon dioxide, nitrogen, and water vapor dominated this early atmosphere. Table 5b-1 below describes the three major stages of development of the atmosphere.Table 5b-1: Evolution of the Earth's atmosphere.Name of StageDuration of Stage (Billions of Years Ago)Main Constituents of the AtmosphereDominant Processes and FeaturesEarly Atmosphere4.4 to 4.0H2O, hydrogen cyanide (HCN), ammonia (NH3), methane (CH4), sulfur, iodine, bromine, chlorine, argonLighter gases like hydrogen and helium escaped to space. ?All water was held in the atmosphere as vapor because of high temperatures.Secondary Atmosphere4.0 to 3.3At 4.0 billion H2O, CO2, and nitrogen (N) dominant. Cooling of the atmosphere causes precipitation and the development of the oceans. ?By 3.0 billion CO2, H2O, N2 dominant. O2 begins to accumulate.Continued release of gases from the lithosphere. ?Water vapor clouds common in the lower atmosphere.Chemosynthetic bacteria appear on the Earth some time between 3.9 and 3.5 billion years ago. Life begins to modify the atmosphere.Living Atmosphere 3.3 to PresentN2 - 78%, O2 - 21%, Argon - 0.9%, CO2 - 0.036%Development, evolution and growth of life increases the quantity of oxygen in the atmosphere from <1% to 21%. ?500 million years ago concentration of atmospheric oxygen levels off.Humans begin modifying the concentrations of some gases in the atmosphere beginning around the year 1700.As the Earth continued to cool, the water vapor found in the atmosphere condensed to form the oceans and other fresh water bodies on the continents. Oxygen began accumulating in the atmosphere through photo-dissociation of O2 from water, and by way of photosynthesis (life). The emergence of living organisms was extremely important in the creation of atmospheric oxygen and ozone. Without ozone, life could not exist on land because of harmful ultraviolet radiation.Most of the build up of oxygen in the atmosphere occurred between 2.1 and 1.5 billion years ago as a direct result of photosynthesis from ocean based plants like algae. At about 450 million years ago, there was enough oxygen in the atmosphere to allow for the development of a stratospheric ozone layer that was thick enough to keep terrestrial life protected from ultraviolet radiation. As a result, terrestrial life began its development and expansion at this time. Table 5b-2 describes the timing of the evolutionary development of some of the Earth's dominant forms of life before and after 450 million years before present (BP).Table 5b-2: Approximate origin time of the major plant and animal anism GroupTime of OriginMarine Invertebrates570 Million Years AgoFish505 Million Years AgoLand Plants438 Million Years AgoAmphibians408 Million Years AgoReptiles320 Million Years AgoMammals208 Million Years AgoFlowering Plants (Angiosperms)140 Million Years Ago?The Natural Spheres GROUP 5From the standpoint of Physical Geography, the Earth can be seen to be composed of four principal components:Lithosphere - describes the solid inorganic portion of the Earth (composed of rocks, minerals and elements). It can be regarded as the outer surface and interior of the solid Earth. On the surface of the Earth, the lithosphere is composed of three main types of rocks:Igneous - rocks formed by solidification of molten magma.Sedimentary - rocks formed by the alteration and compression of old rock debris or organicMetamorphic - rocks formed by alteration of existing rocks by intense heat or pressure.Atmosphere - is the vast gaseous envelope of air that surrounds the Earth. Its boundaries are not easily defined. The atmosphere contains a complex system of gases and suspended particles that behave in many ways like fluids. Many of its constituents are derived from the Earth by way of chemical and biochemical reactions.Hydrosphere - describes the waters of the Earth (see the hydrologic cycle). Water exists on the Earth in various stores, including the atmosphere, oceans, lakes, rivers, soils, glaciers, and groundwater. Water moves from one store to another by way of: evaporation, condensation, runoff, precipitation, infiltration and groundwater flow.Biosphere - consists of all living things, plant and animal. This zone is characterized by life in profusion, diversity, and ingenious complexity. Cycling of matter in this sphere involves not only metabolic reactions in organisms, but also many abiotic chemical reactions.All of these spheres are interrelated to each other by dynamic interactions, like biogeochemical cycling, that move and exchange both matter and energy between the four components.?The Gaia Hypothesis Group 6In 1965, J.E. Lovelock published the first scientific paper suggesting the Gaia hypothesis. The Gaia hypothesis states that the temperature and composition of the Earth's surface are actively controlled by life on the planet. It suggests that if changes in the gas composition, temperature or oxidation state of the Earth are caused by extraterrestial, biological, geological, or other disturbances, life responds to these changes by modifying the abiotic environment through growth and metabolism. In simplier terms, biological responses tend to regulate the state of the Earth's environment in their favor.The evidence for Gaia is as follows:If not continually replaced by biotic activities gases like methane and hydrogen would become non-existant in the atmosphere in a few decades.Carbon dioxide (C02) in the Earth's atmosphere is far less abundant than chemistry alone would allow. If life was deleted carbon dioxide would become 30 times more abundant. Large quantities of carbon dioxide are currently locked up by living organisms.The Sun's energy output has increased by 30% in the past 3.5 billion years. Yet, historical climate data indicates that the temperature of the Earth has only fluctuated by about 5° Celsius from the current average global temperature of 15° Celsius. Computer climate models suggest that a 30% reduction in solar radiation would create a global average temperature of between -10 and -52° Celsius all things being equal. These results indicate that levels of atmospheric carbon dioxide must have been much higher in the past when the Sun was less powerful. Extra atmospheric carbon dioxide would have created a greater greenhouse effect and warmer temperatures. These results also indicate that some mechanism must have removed carbon dioxide from the atmosphere as the Sun's output of radiation increased over the Earth's geologic history. This mechanism is the conversion of atmospheric carbon dioxide into fossilized organic matter (natural gas, oil, coal, limestone, and peat). In other words, Gaia!This theory is important to Physical Geography and other Earth Sciences for the following reasons:The Gaia theory suggests that the abiotic and biotic environment is made up of many complex interrelationships;Many of these complex interrelationships are quite delicate and may be altered by human activity to a breaking point; andThe theory suggests that humans must learn to respect Gaia by reducing their intentional modification of the Earth's abiotic and biotic components.Summary of the ChapterThe nature of the Universe and the Earth are examined in this chapter. The Big Bang theory is presented as a model to explain the origin, history, and future of the Universe. Most cosmologists and physicists believe matter, energy, space, and time in our Universe were created from a huge explosion about 15 billion years ago. Ever since this explosion the Universe has been expanding at the speed of light. About 5 billion years ago our solar system formed. Verification of the Big Bang theory is based on four pieces of evidence.The formation and evolution of the Earth is then explored next. The Earth began forming about 4.6 billion years ago. The timing and development of the Earth's continents and the atmosphere is discussed. It is then suggested that the Earth can be seen to be composed of four principal components: lithosphere, biosphere, atmosphere, and hydrosphere. It is also suggested that linkages exist between the components through biogeochemical cycling.The topic concludes with an examination of the Gaia hypothesis. This theory suggests that life has the ability to control and modify certain aspects of the Earth’s lithosphere, atmosphere and hydrosphere. This modification is done when one of these components is change in a way that is detrimental to living organisms. Life can respond and reverse the changes to the environment through growth to attain the optimum conditions for their survival ................
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