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Space Systems
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Patterns of the apparent motion of the sun, the moon, and stars in the sky can be observed, described, and explained with models.
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The universe began with a period of rapid expansion known as the Big Bang. Nearly all observable matter in the universe is hydrogen or helium, which is formed in the first minutes after the Big Bang.
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A system can be changing but have a stable repeating cycle of changes; such observed regular patterns allow predictions about the system's future.
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Earth and its solar system are part of the Milky Way galaxy, which is one of many galaxies in the universe.
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Earth's spin axis is fixed in direction but tilted relative to its orbit around the sun; the differential intensity of sunlight on different areas of the earth over the year is a result of that tilt, as are the seasons.
The History of the Earth
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The geologic time scale interpreted from rock strata provides a way to organize Earth's history. Earth has changed significantly since its formation along with the rest of the solar system 4.6 billion years ago. Major historical events include the formation of mountain chains and ocean basins, evolution and extinction of particular living organisms, volcanic eruptions, periods of massive glaciation, and the development of watersheds and rivers thorugh glaciation and water erosion.
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Analyses of rock strata and the fossil records provide only relative dates, not an absolute scale.
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Earth's systems interact over scales that range from microspopic to global in size, and operate over fractions of a second to billions of years. These interactions have shaped Earth's history and will determine its future.
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The evolution of life is shaped by Earth's varying geologic conditions. Sudden changes in these conditions have caused mass extinctions in Earth's past. However, these changes, as well as more gradual ones, have also allowed other existing or new life forms as they adapt to new environments.
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Organisms continually evolve to new and often more complex forms as they adpat to new environments.
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The evolution and proliferation of living things over geologic time have in turn changed the rates of weathering and erosion of land surfaces, altering the composition of Earth's soils and atmosphere, and affected the distribution of water in the hydrosphere.
Earth's Interior Processes
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Earth's internal processes are the result of energy flowing and matter cycling within and among the planet's systems. This energy is derived from the Earth's hot interior. The flow of energy and cycling of matter produce chemical and physical changes in Earth's interior materials and living organisms.
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The top part of the mantle, along with the crust, forms structures known as tectonic plates.
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Organisms continually evolve to new more complex forms as they adapt to new environments.
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Humans depend on Earth's interior for many different resources. Minerals and energy resources are limited, and many are not renewable or replaceable over human lifetimes. These resources are distributed unevenly around the planet as a result of past geologic processes.
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Some natural hazards such as volcanic eruptions are preceded by phenomena that allow for reliable predictions. Others, such as earthquakes, occur suddenly and without notice and are not yet predictable. However, mapping the history of natural hazards in a region and developing an understanding of related geologic forces can help forecast the locations and likelihoods of future events.
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Tectonic processes continually generate new ocean sea floor at ridges and destroy old sea floor at trenches.
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Solid rocks can be formed by the cooling of molten rock, the accumulation and consolidation of sediments or the alteration of older rocks by heat, pressure, and fluids.
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Maps of ancient land and water patterns, based on investigation of rocks and fossils, make clear how Earth's plates have moved great distances, collided and spread apart.
Earths' Surface Processes
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Water continually cycles among the land, ocean, and atmosphere via transpiration, evaporation, condensation, precipitation, and the downhill runoff on land. Global movements of water and changes in its chemical phase are driven by sunlight and gravity.
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Surface-related geologic processes create natural resource needs by humans and cause natural hazards that pose challenges to human society.
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Earth's surface processes are the result of energy flowing and matter cycling within and among the planet's surface systems. This energy is derived from electromagnetic radiation from the sun. This flow of energy and cycling of matter produces chemical and physical changes in Earth's surface materials and living organisms.
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Physical and chemical interactions among rocks, sediments, water, air, and plants and animals produce soil.
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Variation in density due to variations in temperature and salinity drive a global pattern of interconnected ocean currents.
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Water's movements both on land and underground cause weathering and erosion, which change the land's surface feature and create underground formations.
Weather & Climate Systems
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Weather and climate are influenced by interactions involving sunlight, the ocean, the atmosphere, ice, landforms, and living things. These interactions vary with latitude, altitude, and local and regional geography, all of which can affect oceanic and atmospheric flow patterns.
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Because these patterns are so complex, weather can only be predicted probabilisticly.
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Humans depend on Earth's ocean, atmosphere and biosphere for many different resources. Fresh water and biosphere resources are limited and many are not renewable or replaceable over human lifetimes. These resources are distributed unevenly around the planet as a result of weather and climate related processes.
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The complex patterns of the changes and the movement of water in the atmosphere, determined by winds, landforms, and ocean temperature and currents, are major determinants of local weather patterns.
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The ocean and land exert major influences on weather and climate by absorbing energy from the sun, releasing it over time, and globally redistributing it via oceanic and atmospheric circulation. The patterns of differential heating, together with Earth's rotation and configuration of continents and oceans, control the large-scale patterns of oceanic and atmospheric circulation.
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Greenhouse gases in the atmosphere absorb and retain the energy radiated from land and ocean surfaces, thereby regulating Earth's average surface temperature and keeping the Earth habitable.
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Organisms ranging from bacteria to humans are major driver of the global carbon cycle, and they influence global climate and by modifying the chemical makeup of the atmosphere.
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Severe weather events are often preceded by observable phenomena that allow for reliable predictions. Constant monitoring of weather hazards in a region and the development of an understanding of related geologic forces can help forecast the locations of likelihoods of future events.
Human Impacts
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Humans have become one of the most significan agents of change in the near-surface Earth systems. Human activities have significantly altered the biosphere, geosphere, hydrosphere, and atmosphere.
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Human activities, such as release of greenhouse gases from burning fossil fuels, are major factors in the current rise in Earth's mean surface temperature.
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As human populations and per capita consumption of natural resources increase, so do the impact on Earth's systems unless the activites and technology involved are engineered otherwise.
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Reducing the amount of greenhouse gases released into the atmosphere can reduce the degree to which global temperatures will increase.
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Continued monitoring of the changes to Earth's surface provide a deeper understanding of the way in which human activities are impacting Earth's systems, providing the basis for social policies and regulation that can reduce these impacts.
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Renewable energy resources and the technology to exploit them are being rapidly developed.
