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Earth System Science The complex and interconnected dynamics of the continents, atmosphere, oceans, ice, and life forms are the subject of earth system science. These interconnected dynamics require an interdisciplinary approach that includes chemistry, physics, biology, mathematics, and applied sciences in order to study the Earth as an integrated system and determine (while considering human impact and interaction) the past, present, and future states of the earth. Scientific inquiry in this field includes exploration of:
Traditional Earth Science Disciplines Modern science is approaching the study of the earth in an integrated fashion that sees the earth as an interconnected system that is impacted by humankind and, therefore, must include social dimensions. Traditionally, though, the following were the earth science disciplines: Geology – This is the study of the origin and structure of the earth and of the changes it has undergone and is in the process of undergoing. Geologists work from the crust inward. Meteorology – This is the study of the atmosphere, including atmospheric pressure, temperature, clouds, winds, precipitation, etc. It is also concerned with describing and explaining weather. Oceanography – This is the study of the oceans, which includes studying their extent and depth, the physics and chemistry of ocean waters, and the exploitation of their resources. Ecology – This is the study of living organisms in relation to their environment and to other living things. It is the study of the interrelations between the different components of the ecosystem. Geological Eras Geologists divide the history of the earth into units of time called eons, which are divided into eras, then into periods, then into epochs and finally into ages. Dates are approximate of course, and there may be variations of a few million years. (Million years ago is abbreviated as Ma.) Some of the most commonly known time periods are: Hadean Eon – About 4.5 to 3.8 billion years ago Archaean Eon – 3.8 to 2.5 billion years ago Proterozoic Eon – 2.5 billion to 542 Ma Phanerozoic Eon – 542 Ma to the present - Paleozoic Era – 542 Ma to 251 Ma ----- Cambrian Period – 542 to 488 Ma ----- Ordovician Period – 488 to 443 Ma ----- Silurian Period – 443 to 416 Ma ----- Devonian Period – 416 to 359 Ma ----- Carboniferous Period – 359 to 290 Ma ----- Permian Period – 290 to 252 Ma - Mesozoic Era – 252 to 65 Ma ----- Triassic Period – 252 to 200 Ma ----- Jurassic Period – 200 to 150 Ma ----- Cretaceous Period – 150 to 65 Ma - Cenozoic Era – 65 Ma to the present ----- Paleogene Period – 65 to 28 Ma ----- Neogene Period – 28 to 2 Ma ----- Quaternary Period – about 2 Ma to the present Development of Life on Earth According to Time Periods The evolution of life on earth is believed to have occurred as follows: Igneous rocks formed. (Hadean Eon) The continents formed. (Archaean Eon) The first multi-cellular creatures such as hydras, jellyfish, and sponges appeared about 600 Ma. Flatworms, roundworms, and segmented worms appeared about 550 Ma. Moss, arthropods, octopus, and eels appeared. (Cambrian Period) Mushrooms, fungi, and other primitive plants appeared; sea animals began to use calcium to build bones and shells. (Ordovician Period) Fish with jaws appeared. (Silurian Period) Fish developed lungs and legs (frogs) and went on land; ferns appeared. (Devonian period) Reptiles developed the ability to lay eggs on land and pine trees appeared. (Carboniferous Period) Dinosaurs dominated the land during the Triassic and Jurassic Periods. Flying insects, birds, and the first flowering plants appeared; dinosaurs died out. (Cretaceous Period) Mammals evolved and dominated; grasses became widespread. (50 Ma) Hominids appeared more than 2 Ma. Hydrosphere and Hydrologic Cycle The hydrosphere is anything on earth that is related to water, whether it is in the air, on land, or in a plant or animal system. A water molecule consists of only two atoms of hydrogen and one of oxygen, yet it is what makes life possible. Unlike the other planets, earth is able to sustain life because its temperature allows water to be in its liquid state most of the time. Water vapor and ice are of no use to living organisms. The hydrologic cycle is the journey water takes as it assumes different forms. Liquid surface water evaporates to form the gaseous state of a cloud, and then becomes liquid again in the form of rain. This process takes about 10 days if water becomes a cloud. Water at the bottom of the ocean or in a glacier is not likely to change form, even over periods of thousands of years. Aquifers An aquifer is an underground water reservoir formed from groundwater that has infiltrated from the surface by passing through the soil and permeable rock layers (the zone of aeration) to a zone of saturation where the rocks are impermeable. There are two types of aquifers. In one, the water is under pressure (confined) as the supply builds up between layers of impermeable rocks and has to move back towards the surface, resulting in a spring or artesian well. The second type of aquifer is called 'unconfined' because it has room to expand and contract, and the water has to be pumped out. The highest level of the aquifer is called the water table. If water is pumped out of the aquifer such that the water table dips in a specific area, that area is called a cone of depression. Biosphere Biosphere is the term used by physical geographers to describe the living world of trees, bugs, and animals. It refers to any place where life exists on earth, and is the intersection of the hydrosphere, the atmosphere, the land, and the energy that comes from space. The biosphere includes the upper areas of the atmosphere where birds and insects can travel, areas deep inside caves, and hydrothermal vents at the bottom of the ocean. Factors that affect the biosphere include: The distance and tilt between the earth and the sun – This produces temperatures that are conducive to life and causes the seasons. Climate, daily weather, and erosion – These change the land and the organisms on and in it. Earthquakes, tornadoes, volcanoes, tsunamis, and other natural phenomena – These all change the land. Chemical erosion – This changes the composition of rocks and organic materials. Biological erosion – This is bacteria and single-celled organisms breaking down organic and inorganic materials. Ecological System and Biome
An ecological system, or ecosystem, is the community of all the living organisms in a specific area interacting with non-living factors such as temperature, sunlight, atmospheric pressure, weather patterns, wind, types of nutrients, etc. An ecosystem's development depends on the energy that passes in and out of it. The boundaries of an ecosystem depend on the use of the term, whether it refers to an ecosystem under a rock or in a valley, pond, or ocean. A biome is a general ecosystem type defined by the plants and animals that live there and the local climate patterns. Examples include tropical rainforests or savannas, deserts, grasslands, deciduous forests, tundra, woodlands, and ice caps. There can be more than one type of biome within a larger climate zone. The transition area between two biomes is an ecotone, which may have characteristics of both biomes. Erosion Erosion is the process that breaks down matter, whether it is a rock that is broken into pebbles or mountains that are rained on until they become hills. Erosion always happens in a downhill direction. The erosion of land by weather or breaking waves is called denudation. Mass wasting is the movement of masses of dirt and rock from one place to another. This can occur in two ways: mechanical (such as breaking a rock with a hammer) or chemical (such as pouring acid on a rock to dissolve it). If the material changes color, it indicates that a break down was chemical in nature. Whatever is broken down must go somewhere, so erosion eventually builds something up. For example, an eroded mountain ends up in a river that carries the sediment towards the ocean, where it builds up and creates a wetland or delta at the mouth of the river. Climates Scientists have determined the following different types of climates: Polar (ice caps) Polar (tundra) Subtropical (dry summer) Subtropical (dry winter) Subtropical (humid) Subtropical (marine west coast) Subtropical (Mediterranean) Subtropical (wet) Tropical (monsoon) Tropical (savannah/grasslands) Tropical (wet) Several factors make up and affect climates. These include: Temperature Atmospheric pressure The number of clouds and the amount of dust or smog Humidity Winds The moistest and warmest of all the climates is that of the tropical rainforest. It has daily convection thunderstorms caused by the surface daytime heat and the high humidity, which combine to form thunderclouds. Layers of the Earth The earth has several distinct layers, each with its own properties: Crust – This is the outermost layer of the earth that is comprised of the continents and the ocean basins. It has a variable thickness (35-70 km in the continents and 5-10 km in the ocean basins) and is composed mostly of alumino-silicates. Mantle – This is about 2900 km thick, and is made up mostly of ferro-magnesium silicates. It is divided into an upper and lower mantle. Most of the internal heat of the earth is located in the mantle. Large convective cells circulate heat, and may cause plate tectonic movement. Core – This is separated into the liquid outer core and the solid inner core. The outer core is 2300 km thick (composed mostly of nickel-iron alloy), and the inner core (almost entirely iron) is 12 km thick. The earth's magnetic field is thought to be controlled by the liquid outer core. Composition of Earth's Atmosphere The earth's atmosphere is 79% nitrogen, 20% oxygen, and 1% other gases. The oxygen was originally produced almost entirely by algae-type plants. The atmosphere has four layers: Troposphere – This is the layer closest to the earth where all weather takes place. It is the region that contains rising and falling packets of air. Air pressure at sea level is 0.1 atmospheres, but the top of the troposphere is about 10% of that amount. Stratosphere – In this layer, air flow is mainly horizontal. The upper portion has a thin layer of concentrated ozone (a reactive form of oxygen) that is largely responsible for absorbing the sun's ultraviolet rays. Mesosphere – This is the coldest layer. Temperatures drop to -100°C at the top. Thermosphere – This is divided into the lower ionosphere and the higher exosphere. This layer is very thin and has many ionized atoms with a net electrical charge. The aurora and Van Allen Belts are here. This layer also absorbs the most energetic photons from the sun and reflects radio waves, enabling long distance radio communication. Paleontology Paleontology is the study of prehistoric plant and animal life through the analysis of fossil remains. These fossils reveal the ecologies of the past and the path of evolution for both extinct and living organisms. A historical science, paleontology seeks information about the identity, origin, environment, and evolution of past organisms and what they can reveal about the past of the earth as a whole. Paleontology explains causes as opposed to conducting experiments to observe effects. It is related to the fields of biology, geology, and archaeology, and is divided into several sub-disciplines concerned with the types of fossils studied, the process of fossilization, and the ecology and climate of the past. Paleontologists also help identify the composition of the earth's rock layers by the fossils that are found, thus identifying potential sites for oil, mineral, and water extraction. Determining the Order in Which Geologic Events Occurred Using the Rock Record The Law of Superposition logically assumes that the bottom layer of a series of sedimentary layers is the oldest, unless it has been overturned or older rock has been pushed over it. In addition, since igneous intrusions can cut through or flow above other rocks, these other rocks are older. For example, molten rock (lava) flows out over already present, older rocks. Another guideline for the rock record is that rock layers are older than the folds and faults in them because the rocks must exist before they can be folded or faulted. If a rock contains atomic nuclei, reference tables of the half-lives of commonly used radio isotopes can be used to match the decay rate of known substances to the nuclei in a rock, and thereby determine its age. Ages of rocks can also be determined from contact metamorphism, the re-crystallization of pre-existing rocks due to changes in physical and chemical conditions, such as heat, pressure, and chemically active fluids that might be present in lava or polluted waters. Matching Rocks and Geologic Events in One Place with Those of Another Geologists physically follow rock layers from one location to another by a process called 'walking the outcrop.' Geologists walk along the outcropping to see where it goes and what the differences and similarities of the neighboring locations they cross are. Similar rock types or patterns of rock layers that are similar in terms of thickness, color, composition, and fossil remains tell geologists that two locations have a similar geologic history. Fossils are found all over the earth, but are from a relatively small time period in earth's history. Therefore, fossil evidence helps date a rock layer, regardless of where it occurs. Volcanic ash is a good time indicator since ash is deposited quickly over a widespread area. Matching the date of an eruption to the ash allows for a precise identification of time. Similarly, the meteor impact at the intersection of the Cretaceous and Tertiary Periods left a time marker. Wherever the meteor's iridium content is found, geologists are able to date rock layers. Sequencing the Earth's Geologic History from the Fossil and Rock Record Reference tables are used to match specimens and time periods. For example, the fossil record has been divided into time units of the earth's history. Rocks can therefore be dated by the fossils found with them. There are also reference tables for dating plate motions and mountain building events in geologic history. Since humans have been around for a relatively short period of time, fossilized human remains help to affix a date to a location. Some areas have missing geologic layers because of erosion or other factors, but reference tables specific to a region will list what is complete or missing. The theory of uniformitarianism assumes that geologic processes have been the same throughout history. Therefore, the way erosion or volcanic eruptions happen today is the same as the way these events happened millions of years ago because there is no reason for them to have changed. Therefore, knowledge about current events can be applied to the past to make judgments about events in the rock record. Revealing Changes in Earth's History by the Fossil and Rock Records Fossils can show how animal and plant life have changed or remained the same over time. For example, fossils have provided evidence of the existence of dinosaurs even though they no longer roam the earth, and have also been used to prove that certain insects have been around for hundreds of millions of years. Fossils have been used to identify four basic eras: Proterozoic, the age of primitive life; Paleozoic, the age of fishes; Mesozoic, the age of dinosaurs; and Cenozoic, the age of mammals. Most ancient forms of life have disappeared, and there are reference tables that list when this occurred. Fossil records also show the evolution of certain life forms, such as the horse from the eohippus. However, the majority of changes do not involve evolution from simple to complex forms, but rather an increase in the variety of forms. Mountains A mountain is a portion of the earth that has been raised above its surroundings by volcanic action or tectonic plate movement. Mountains are made up of igneous, metamorphic, and sedimentary rocks, and most lie along active plate boundaries. There are two major mountain systems. The Circum-Pacific encircles the entire Pacific Ocean, from New Guinea up across Japan and the Aleutians and down to southern South America. The Alpine-Himalaya stretches from northern Africa across the Alps and to the Himalayas and Indonesia. Orogeny is the term for the process of natural mountain formation. Therefore, physical mountains are orogens. Folded mountains are created through the folding of rock layers when two crustal plates come together. The Alps and Himalayas are folded mountains. The latter was formed by the collision of India with Asia. Fault-block mountains are created from the tension forces of plate movements. These produce faults that vertically displace one section to form a mountain. Dome mountains are created from magma pushing up through the earth's crust. Volcanoes and Volcanic Mountains Volcanoes are classified according to their activity level. An active volcano is in the process of erupting or building to an eruption; a dormant volcano has erupted before and may erupt again someday, but is not currently active; and an extinct volcano has died out volcanically and will not erupt ever again. Active volcanoes endanger plant and animal life, but lava and ash add enriching minerals to the soil. There are three types of volcanic mountains: Shield volcanoes are the largest volcanic mountains because of a repeated, viscous lava flow from small eruptions over a long period of time that cause the mountain to grow. Cinder cone volcanoes, or linear volcanoes, are small in size, but have massive explosions through linear shafts that spread cinders and ash around the vent. This results in a cone-shaped hill. Composite volcanoes get their name from the mix of lava and ash layers that build the mountain. Subdivisions of Rock The three major subdivisions of rock are: Igneous (magmatites) – This type is formed from the cooling of liquid magma. In the process, minerals crystallize and amalgamate. If solidification occurs deep in the earth (plutonic rock), the cooling process is slow. This allows for the formation of large crystals, giving rock a coarse-grained texture (granite). Quickly cooled magma has a glassy texture (obsidian). Metamorphic – Under conditions of high temperature and pressure within the earth's crust, rock material melts and changes structure, transitioning or metamorphosing into a new type of rock with different minerals. If the minerals appear in bands, the rock is foliated. Examples include marble (unfoliated) and slate (foliated). Sedimentary – This is the most common type of rock on earth. It is formed by sedimentation, compaction, and then cementation of many small particles of mineral, animal, or plant material. There are three types of sedimentary rocks: clastic, clay, and sand that came from disintegrated rocks; chemical (rock salt and gypsum), formed by evaporation of aqueous solutions; and biogenic (coal), formed from animal or plant remnants. Glaciers Glaciers start high in the mountains, where snow and ice accumulate inside a cirque (a small semicircular depression). The snow becomes firmly packed into masses of coarse-grained ice that are slowly pulled down a slope by gravity. Glaciers grow with large amounts of snowfall and retreat (diminish) if warm weather melts more ice than can be replaced. Glaciers once covered large areas of both the northern and southern hemispheres with mile-thick ice that carved out valleys, fjords, and other land formations. They also moved plants, animals, and rocks from one area to another. There were two types of glaciers: valley, which produced U-shaped erosion and sharp-peaked mountains; and continental, which moved over and rounded mountain tops and ridges. These glaciers existed during the ice ages, the last of which occurred from 2.5 million years ago to 12,000 years ago.
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