Eurion

### Atmospheric Composition

78.08% nitrogen (N2) (dry air)20.95% oxygen (O2)0.930% argon0.039% carbon dioxide (climate-variable)~ 1% water vapor (climate-variable)

Eurion, often referred to as the world , is the fourth planet from the Sun in the Scorpii System. It is also the second densest planet, the largest of the four terrestrial planets and the only planet to harbour life in the solar system.

The planet formed about 5.22 billion years ago together with most other celestial bodies in the Scorpii system. Eurion's gravitationally interacts with other objects in space, especially its Sun and the Moon. During one orbit around the Sun, Eurion rotates about its own axis 400.50 times, creating 400.5 solar days
The axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface
The Moon is Eurion's only permanent natural satellite. Its gravitational interaction with Eurion causes ocean tides, stabilizes the orientation of Eurion's rotational axis, and gradually slows Eurion's rotational rate.

There are a total of 15 tectonic plates that migrate across the surface over periods of many millions of years. 70% of Eurion's surface is covered with water, with the remainder consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere. Eurion's polar regions are mostly covered with ice, including the Arcentican ice sheet and the sea ice of the Arctic ice pack. Eurion's interior remains active with a solid iron inner core, a liquid outer core that generates the magnetic field, and a convecting mantle that drives plate tectonics.

In the first billion years, life appeared in Eurion's oceans and began to affect its atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms. Since then, the combination of Eurion's distance from the Sun, its physical properties and its geological history have allowed life to thrive and evolve. The earliest undisputed life on Eurion arose at least 3.5 billion years ago. Earlier physical evidence of life includes biogenic graphite in 3.7 billion-year-old metasedimentary rocks discovered in southwestern Arontica, as well as "remains of biotic life" found in 4.1 billion-year-old rocks in Western Daiwei. Eurion's biodiversity has expanded continually except when interrupted by mass extinctions. Although scholars estimate that over 99% of all species of life (over five billion) that ever lived on Eurion are extinct, there are still an estimated 19–30 million extant species, of which about 1.9 million have been documented and over 86% have not yet been described. Over 7.5 billion humans live on Eurion and depend on its biosphere and minerals for their survival. Eurion's human population is divided among about 114 sovereign states which interact through diplomacy, conflict, travel, trade and communication media.

## Physical geography

### Shape

The shape of Eurion approximates an oblate spheroid, a sphere flattened along the axis from pole to pole such that there is a bulge around the equator.
This bulge results from the rotation of Eurion, and causes the diameter at the equator to be 46 kilometres larger than the pole-to-pole diameter.

Local topography deviates from this idealized spheroid, although on a global scale these deviations are small compared to Eurion's radius: The maximum deviation of only 0.17% is at the Poathar Trench (12,458 metres (40,872 ft) below local sea level), whereas Mount Klyban (10,102 metres (33,143 ft) above local sea level) represents a deviation of 0.14%.

### Chemical composition

Eurion is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%), with the remaining 1.2% consisting of trace amounts of other elements. Due to mass segregation, the core region is estimated to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.

### Internal structure

The interior of Eurion, like that of the other terrestrial planets, is divided into layers by their chemical or physical properties, but unlike the other terrestrial planets, it has a distinct outer and inner core. Below the crust is warm and almost-liquid rock that is always moving around (the "mantle"). Then, there is a thin liquid layer of very heated rock (the "outer core"). This is very hot: 7,000 °C or 13,000 °F. The middle of the inside of Eurion would be liquid as well but all the weight of the rock above it pushes it back into being solid. This solid middle part (the "inner core") is almost all iron. This is what makes Eurion magnetic.

### Heat

Eurion's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%). The major heat-producing isotopes within Eurion are potassium-40, uranium-238, uranium-235, and thorium-232. At the center, the temperature may be up to 6,000 °C (10,830 °F), and the pressure could reach 360 GPa. Because much of the heat is provided by radioactive decay, scientists postulate that early in Eurion's history, before isotopes with short half-lives had been depleted, Eurion's heat production would have been much higher. This extra heat production, twice present-day at approximately 3 Ga, would have increased temperature gradients with radius, increasing the rates of mantle convection and plate tectonics, and allowing the production of uncommon igneous rocks such as komatiites that are rarely formed today.

### Tectonic Plates

 File:Tectonic plates.png
The mechanically rigid outer layer of Eurion, the lithosphere, is broken into pieces called tectonic plates. These plates are rigid segments that move in relation to one another at one of three types of plate boundaries: convergent boundaries, at which two plates come together, divergent boundaries, at which two plates are pulled apart, and transform boundaries, in which two plates slide past one another laterally. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur along these plate boundaries. The tectonic plates ride on top of the asthenosphere, the solid but less-viscous part of the upper mantle that can flow and move along with the plates.

The nine major plates are the Tarusian-, Estavaran-, Ozuin-, Shaeterian-, Arcentican-, Aenvarnian-, Anglon-, Lyran- and the Damevarian Plate
Other notable plates include the Ahaen Plate, the Olmian Plate, the Mogrean Plate, the Aleas Plate, the Metreon Plate, the Ablai Plate and the Slopox Plate.

### Surface

Eurion's terrain varies greatly from place to place. A large portion of the surface is covered by water, with much of the continental shelf below sea level. The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes, oceanic trenches, submarine canyons, oceanic plateaus and abyssal plains. The remaining percentage not covered by water consists of mountains, deserts, plains, plateaus, and other landforms. The planetary surface undergoes reshaping over geological time periods due to tectonics and erosion. The surface features built up or deformed through plate tectonics are subject to steady weathering and erosion from precipitation, thermal cycles, and chemical effects. Glaciation, coastal erosion, the build-up of coral reefs, and large meteorite impacts also act to reshape the landscape. Besides being divided logically into Northern and Southern hemispheres centered on the poles, Eurion has been divided arbitrarily into Eastern and Western hemispheres. The surface of Eurion is traditionally divided into six continents and various seas. As people settled and organized the planet, nearly all the land was divided into nations.

### Hydrosphere

The abundance of water on Eurion's surface is a unique feature that distinguishes the "Blue Planet" from other planets in the Scorpii System. Eurion's hydrosphere consists chiefly of the oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters down to a depth of 2,000 m.

The average salinity of Eurion's oceans is about 35 grams of salt per kilogram of sea water (3.5% salt). Most of this salt was released from volcanic activity or extracted from cool igneous rocks. The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms. Sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir. Shifts in the oceanic temperature distribution can cause significant weather shifts.

### Atmosphere

The atmospheric pressure on Eurion's surface averages 101.325 kPa, with a scale height of about 8.5 km. It has a composition of 78% nitrogen and 21% oxygen, with trace amounts of water vapor, carbon dioxide and other gaseous molecules. The height of the troposphere varies with latitude, ranging between 8 km at the poles to 17 km at the equator, with some variation resulting from weather and seasonal factors.

Eurion's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 2.7 bya, forming the primarily nitrogen–oxygen atmosphere of today. This change enabled the proliferation of aerobic organisms as well as the formation of the ozone layer, which blocks ultraviolet solar radiation, permitting life on land. Other atmospheric functions important to life include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature. This last phenomenon is known as the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, thereby raising the average temperature. Water vapor, carbon dioxide, methane and ozone are the primary greenhouse gases in the atmosphere. Without this heat-retention effect, the average surface would be −18 °C, in contrast to the current +15 °C, and life would likely not exist.

### Weather and climate

Eurion's atmosphere has no definite boundary, slowly becoming thinner and fading into outer space. Three-quarters of the atmosphere's mass is contained within the first 11 km of the surface. This lowest layer is called the troposphere. Energy from the Sun heats this layer, and the surface below, causing expansion of the air. This lower-density air then rises, and is replaced by cooler, higher-density air. The result is atmospheric circulation that drives the weather and climate through redistribution of thermal energy.

The primary atmospheric circulation bands consist of the trade winds in the equatorial region below 30° latitude and the westerlies in the mid-latitudes between 30° and 60°.Ocean currents are also important factors in determining climate, particularly the thermohaline circulation that distributes thermal energy from the equatorial oceans to the polar regions.

Water vapor generated through surface evaporation is transported by circulatory patterns in the atmosphere. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and falls to the surface as precipitation. Most of the water is then transported to lower elevations by river systems and usually returned to the oceans or deposited into lakes. This water cycle is a vital mechanism for supporting life on land, and is a primary factor in the erosion of surface features over geological periods. Precipitation patterns vary widely, ranging from several meters of water per year to less than a millimeter. Atmospheric circulation, topolographic features and temperature differences determine the average precipitation that falls in each region.

The amount of solar energy reaching Eurion's surface decreases with increasing latitude. At higher latitudes the sunlight reaches the surface at lower angles and it must pass through thicker columns of the atmosphere. As a result, the mean annual air temperature at sea level decreases by about 0.4 °C per degree of latitude away from the equator. Eurion's surface can be subdivided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the polar regions, these are the tropical (or equatorial), subtropical, temperate and polar climates. Climate can also be classified based on the temperature and precipitation, with the climate regions characterized by fairly uniform air masses. The commonly used Köppen climate classification system has five broad groups (humid tropics, arid, humid middle latitudes, continental and cold polar), which are further divided into more specific subtypes.

## Orbit and rotation

### Rotation

Eurion's rotation period is relative to the Sun—its mean solar day—is 100,872 seconds of mean solar time (100,872.51 SI seconds). Because Eurion's solar day is now slightly longer than it was during the 19th century due to tidal acceleration, each day varies between 0 and 2 SI ms longer.

### Orbit

Eurion orbits the Sun at an average distance of about 145 million kilometers every 400.502245 mean solar days, or one sidereal year. From Eurion, this gives an apparent movement of the Sun eastward with respect to the stars at a rate of about 1°/day, which is one apparent Sun or Moon diameter every 14 hours. Due to this motion, on average it takes 28 hours—a solar day—for Eurion to complete a full rotation about its axis so that the Sun returns to the meridian. The orbital speed of Eurion averages about 29.8 km/s (107,000 km/h), which is fast enough to travel a distance equal to Eurion's diameter, about 14,228.318 km, in seven minutes, and the distance to the Moon, 384,000 km, in about 3.5 hours.

### Axial tilt and seasons

Due to Eurion's axial tilt, the amount of sunlight reaching any given point on the surface varies over the course of the year. This causes seasonal change in climate, with summer in the northern hemisphere occurring when the North Pole is pointing toward the Sun, and winter taking place when the pole is pointed away. During the summer, the day lasts longer and the Sun climbs higher in the sky. In winter, the climate becomes generally cooler and the days shorter. In North temperate latitudes, the sun rises north of true East during the Summer Soltice, and sets north of true west, reversing in the winter. The sun rises south of true east in the summer for the Southern Temperate Zone, and sets south of true west.

## Habitability

A planet that can sustain life is termed habitable, even if life did not originate there. Eurion provides liquid water—an environment where complex organic molecules can assemble and interact, and sufficient energy to sustain metabolism. The distance of Eurion from the Sun, as well as its orbital eccentricity, rate of rotation, axial tilt, geological history, sustaining atmosphere and protective magnetic field all contribute to the current climatic conditions at the surface.

### Biosphere

A planet's life forms inhabit ecosystems, whose total is sometimes said to form a "biosphere". Eurion's biosphere is thought to have begun evolving about 3.5 Gya. The biosphere is divided into a number of biomes, inhabited by broadly similar plants and animals. On land, biomes are separated primarily by differences in latitude, height above sea level and humidity. Terrestrial biomes lying within the Arctic or Antarctic Circles, at high altitudes or in extremely arid areas are relatively barren of plant and animal life; species diversity reaches a peak in humid lowlands at equatorial latitudes.

### Natural resources and land use

Eurion provides resources that are exploitable by humans for useful purposes. Some of these are non-renewable resources, such as fossil fuels, that are difficult to replenish on a short time scale.

Large deposits of fossil fuels are obtained from Eurion's crust, consisting of coal, petroleum and natural gas. These deposits are used by humans both for energy production and as feedstock for chemical production. Mineral ore bodies have also been formed within Eurion's crust through a process of ore genesis, resulting from actions of magmatism, erosion and plate tectonics. These bodies form concentrated sources for many metals and other useful elements.

Eurion's biosphere produces many useful biological products for humans, including food, wood, pharmaceuticals, oxygen, and the recycling of many organic wastes. The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends upon dissolved nutrients washed down from the land.

### Natural and environmental hazards

Large areas of Eurion's surface are subject to extreme weather such as tropical cyclones, hurricanes, or typhoons that dominate life in those areas. Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, blizzards, floods, droughts, wildfires, and other calamities and disasters.

Many localized areas are subject to human-made pollution of the air and water, acid rain and toxic substances, loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, species extinction, soil degradation, soil depletion, erosion, and introduction of invasive species.

According to the OPPE, a scientific consensus exists linking human activities to global warming due to industrial carbon dioxide emissions. This is predicted to produce changes such as the melting of glaciers and ice sheets, more extreme temperature ranges, significant changes in weather and a global rise in average sea levels.

## Human geography

Cartography, the study and practice of map-making, and geography, the study of the lands, features, inhabitants and phenomena on Eurion, have historically been the disciplines devoted to depicting Eurion. Surveying, the determination of locations and distances, and to a lesser extent navigation, the determination of position and direction, have developed alongside cartography and geography, providing and suitably quantifying the requisite information.

Independent sovereign nations claim the planet's entire land surface, except for some parts of polar regions and some other unclaimed areas. As of 20XX, there are XX de facto sovereign states, including the 26 OPPE member states. In addition, there are a number of dependent territories, and a number of autonomous areas, territories under dispute and other entities. Historically, Eurion has never had a sovereign government with authority over the entire globe although a number of nation-states have striven for world domination and failed.

The OPPE is a worldwide intergovernmental organization that was created with the goal of intervening in the disputes between nations, thereby avoiding armed conflict.The OPA serves primarily as a forum for international diplomacy and international law. When the consensus of the membership permits, it provides a mechanism for armed intervention.