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Space Systems
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The star called the sun is changing and will burn out over a lifespan of approximately 10 billion years.
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The sun is one of more than 200 billion stars in the Milky Way galaxy, and the Milky Way is just one of hundreds of billions of galaxies in the universe.
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The spectra and brightness of stars are used to identify their compositional elements, movements, and distance from Earth and to develop explanations about the formation, age, and composition of the universe. The Big Bang theory is supported by the fact that it provides an explanation of observations of distant galaxies receding from our own, of the measured composition of stars and nonstellar gases, and of the maps of spectra of the primordial radiation that fills the universe.
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Other than the hydrogen and helium formed at the time of the Big Bang, nuclear fusion iwthin stars produces all atomic nuclei lighter than and including iron, and the process releases electromagnetic energy. Heavier elements are produced when certain massive stars achieve supernova stage and explode.
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Kepler's laws describe common features of the motions of orbiting objects, including their elliptical paths. Orbits may change due to gravitational effects from, or collisions with, other objects in the solar system.
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Cyclic changes in the shape of Earth's orbit around the sun, together with changes in the orientation of the planet's axis of rotation, have altered the intensity and distribution of sunlight falling on the Earth. These changes, both occuring over tens to hundreds of thousands of years, cause cycles of ice ages and other gradual climate changes.
History of Earth
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Radioactive decay lifetimes and isotopic content in rocks provide a way of dating rock formations and thereby fixing the scale of geologic time.
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Continental Rocks, which can be older than 4 billion years, are generally much older than the rocks of the ocean floor, which are less than 200 million years old.
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Although active geologic processes, such as plate tectonics and erosion, have destroyed or altered most of the very early rock records on Earth, other objects in the solar system, such as lunar rocks, asteroids, and meteorites have changed little over billions of years. Studying these objects can provide information about Earth's formation and early history.
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Plate tectonics is the unifying theory that explains the past and current movements of the rocks at Earth's surface and provides a framework for understanding its geologic history.
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Plate movements are responsible for most continental and ocean floor features and for the distribution of most rocks and minerals with Earth's crust.
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The many dynamic and delicate feedbacks among the biosphere, geosphere, hydosphere, and atmosphere cause a continual co-evolution of Earth's surface and the life that exists on it.
Earth's Systems
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Evidence from drill cores, gravity, seismic waves and laboratory experiments on Earth materials, reconstructions of historical changes in Earth's surface and its magnetic field, and an understanding of geophysical and geochemical processes lead to a mode of Earth with a hot but solid inner core, a liquid outer core, and a solid mantle and the crust.
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Motions of the mantle and its plates occur primarily through termal convection, which involves the cycling of matter due to the outward flow of energy from Earth's interior and the increased downward gravitational pull of denser mantle material.
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Earth's systems interact over a wide range of temporal and spatial scales and continually react to changing influences, including those from human activities. Components of Earth's systems may appear stable, change slowly over long periods of time, or change abruptly. Changes in part of one system can cause dynamic feedback that can increase or decrease the original changes, further changing that system or other systems in ways thar are often surprising and complex.
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Weather is driven by interactions of the geosphere, hydrosphere, and atmosphere.
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The radioactive decay of unstable isotopes continually generate new energy within Earth's crust and mantle, providing the primary source of heat that drives mantle convection. Plate tectonics can be viewed as the surface expression of mantle convection.
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The abundance of liquid water on Earth's surface and its unique combination of physical and chemical properties are central to the planet's dynamics. These properties include water's exceptional capacity to absorb/store/release large amounts of energy, transmit sunlight, expand upon freezing, dissolve, and transport materials and lower the viscosities and melting points of rocks.
Climate Change
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The foundation of Earth's global climate systems is the electromagnetic radiation from the sun, as well as its reflection, absorption, storage, and redistribution among the atmosphere, ocean, and land systems, and this energy's re-radiation into space. Climate change can occur when certain parts of these systems are altered.
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The geological record shows that changes to global and regional climate can be caused by interactions among changes in the sun's energy output or Earth's orbit, tectonic events, ocean circulation, volcanic activity, glaciers, vegationa, and human activities. These changes can occur on a variety of time scales from sudden to immediate to very long-term tectonic cycles.
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Geologic evidence indicates that past climate changes were either sudden changes caused by alterations in the atmosphere; longer-term changes due to variations in solar output, Earth's orbit, or the orientation of its axis; or even more gradual atmospheric changes due to plants and other organisms that captured carbon dioxide and released oxygen. The time scales of these changes varied from a few to millions of years. Changes in atmosphere due to human activity have increased carbon dioxide concentrations and thus affect climate.
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Global climate models are often used to understand the provess of climate change because these changes are complex and can occur slowly over Earth's history. Global climate modles incorporate scientists' best knowledge of the physical and chemical processes and of the interactions of relevant systems. They are tested by their ability to fit past climate variations.
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Current models predict that although future regional climate changes will be complex and varied, average global temperatures will continue to rise. The outcomes predicted by global climate models strongly depends on the amounts of human-generated greenhouse gases added to the atmosphere each year and by the ways in which these gases are absorbed by the ocean and biosphere. hence, the outcomes depend on human behaviors as well as on natural factors that involve complex feedbacks among Earth's systems.
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Though the magnitudes of human impacts are greater than they have ever been, so too are human abilitiies to model, predict, and manage current and future impacts.
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Thus science and engineering will be essential both to understanding the possible impacts of global climate change and in forming decisions about how to slow its rate and consequences for humanity as well as for the rest of the planet.
Human Sustainability
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Resources availability has guided the development of human society. Resource availability affects geopolitical relationships and can limit development.
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All forms of energy production and other resource extraction have associated economic, social, environmental, and geopolitical costs and risks as well as benefits. New technologies and social regulations can change the balance of these factors.
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As the global human population increases and people's demand for better living conditions increase, resources considered available in the past, such as land for agriculture or drinkable water, are becoming scarcer and more valued.
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Natural hazards and other geologic events have shaped the course of human history by destroying buildings and cities, eroding land, changing the courses of rivers, and reducing the amount of arable land. These events have significantly altered the size of human populations and have driven human migrations.
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Natural hazards can be local, regional, or global in origin,, and their risk increases as population grows. Humans activities can contribute to the frequency and intensity of some natural hazards.
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The sustainabiliity of human societies and the biodiversity that supports them requires responsible management of natural resources.
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Scientists and engineers can make major contributions by developing technologies that address problems like pollution and waste without degrading ecosystems. When the source of an environmental problem is understood and international agreement can be reached, human activities can be regulated to mitigate global impacts.
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Through computer simulations and other studies, important discoveries are still being made about how the ocean, atmosphere, and biosphere interact and are modified in response to human activities and changes in human activities.
