question: Why is the pressure at the center of the earth higher than on the surface?
comment: Pressure is stuff pushing on you. If you stand on a chair vs hold a chair above your head there is a big different in amount of stuff pushing down on you (one chairs worth). At the center of the earth there is one earths worth of stuff pushing down on you.
passages: Section::::Mechanism.
  
  Atmospheric pressure is caused by the gravitational attraction of the planet on the atmospheric gases above the surface, and is a function of the mass of the planet, the radius of the surface, and the amount and composition of the gases and their vertical distribution in the atmosphere. It is modified by the planetary rotation and local effects such as wind velocity, density variations due to temperature and variations in composition.
  
  Section::::Mean sea-level pressure.
   Section::::Physical properties.:Pressure and gravity.
  
  The pressure in the Earth's inner core is slightly higher than it is at the boundary between the outer and inner cores: it ranges from about .
  
  The acceleration of gravity at the surface of the inner core can be computed to be 4.3 m/s; which is less than half the value at the surface of the Earth (about 10 m/s).
  
  Section::::Physical properties.:Density and mass.
   BULLET::::- Ahead of embedded shortwave troughs, which have smaller wavelengths.
  
  Diverging winds aloft ahead of these troughs cause atmospheric lift within the troposphere below, which lowers surface pressures as upward motion partially counteracts the force of gravity.
   CoP and center of gravity (CoG) are both related to balance in that they are dependent on the position of the body with respect to the supporting surface. Center of gravity is subject to change based on posture. Center of pressure is the location on the supporting surface where the resultant vertical force vector would act if it could be considered to have a single point of application.
   The typical atmospheric pressure at the top of Olympus Mons is 72 pascals, about 12% of the average Martian surface pressure of 600 pascals. Both are exceedingly low by terrestrial standards; by comparison, the atmospheric pressure at the summit of Mount Everest is 32,000 pascals, or about 32% of Earth's sea level pressure. Even so, high-altitude orographic clouds frequently drift over the Olympus Mons summit, and airborne Martian dust is still present. Although the average Martian surface atmospheric pressure is less than one percent of Earth's, the much lower gravity of Mars increases the atmosphere's scale height; in other words, Mars's atmosphere is expansive and does not drop off in density with height as sharply as Earth's.
   "Surface pressure" is the atmospheric pressure at a location on Earth's surface (terrain and oceans). It is directly proportional to the mass of air over that location.
  
  For numerical reasons, atmospheric models such as general circulation models (GCMs) usually predict the nondimensional "logarithm of surface pressure".
   Section::::Hydrostatic example (dam).
  
  Since the forces of water on a dam are hydrostatic forces, they vary linearly with depth. The total force on the dam is then the integral of the pressure multiplied by the width of the dam as a function of the depth. The center of pressure is located at the centroid of the triangular shaped pressure field formula_1 from the top of the water line. The hydrostatic force and tipping moment on the dam about some point can be computed from the total force and center of pressure location relative to the point of interest.
   High-pressure area
  
  A high-pressure area, high, or anticyclone, is a region where the atmospheric pressure at the surface of the planet is greater than its surrounding environment.
  
  Winds within high-pressure areas flow outward from the higher pressure areas near their centers towards the lower pressure areas further from their centers. Gravity adds to the forces causing this general movement, because the higher pressure compresses the column of air near the center of the area into greater density – and so greater weight compared to lower pressure, lower density, and lower weight of the air outside the center.
   At low altitudes above sea level, the pressure decreases by about for every 100 metres. For higher altitudes within the troposphere, the following equation (the barometric formula) relates atmospheric pressure "p" to altitude "h":
  
  formula_1
  
  where the constant parameters are as described below:
  
  Section::::Local variation.
  
  Atmospheric pressure varies widely on Earth, and these changes are important in studying weather and climate. See pressure system for the effects of air pressure variations on weather.
   where is the gravitational constant and is the total mass enclosed within radius . If the Earth had a constant density , the mass would be and the dependence of gravity on depth would be
  
  If the density decreased linearly with increasing radius from a density at the center to at the surface, then , and the dependence would be
  
  The actual depth dependence of density and gravity, inferred from seismic travel times (see Adams–Williamson equation), is shown in the graphs below.
  
  Section::::Variation in magnitude.:Local topography and geology.
   Section::::Importance.
   Pressure on Earth varies with the altitude of the surface; so air pressure on mountains is usually lower than air pressure at sea level. Pressure varies smoothly from the Earth's surface to the top of the mesosphere. Although the pressure changes with the weather, NASA has averaged the conditions for all parts of the earth year-round. As altitude increases, atmospheric pressure decreases. One can calculate the atmospheric pressure at a given altitude. Temperature and humidity also affect the atmospheric pressure, and it is necessary to know these to compute an accurate figure. The graph at right was developed for a temperature of 15 °C and a relative humidity of 0%.
   experienced by a body within the Earth is proportional to the
  
  ratio of the distance from the center formula_3 to the Earth's radius formula_4.
  
  This is because underground at distance formula_3 from the center is like
  
  being on the surface of a planet of radius formula_3, within a hollow sphere
  
  which contributes nothing.
  
  On the surface, formula_8, so the gravitational acceleration is formula_9. Hence, the gravitational acceleration at formula_3 is
  
  Section::::Mathematical derivation.:Diametric path to antipodes.
  
  In the case of a straight line through the center of the Earth, the
   Section::::Connection to wind.
   The average atmospheric pressure at sea level is defined by the International Standard Atmosphere as . This is sometimes referred to as a unit of standard atmospheres (atm). Total atmospheric mass is 5.1480×10 kg (1.135×10 lb), about 2.5% less than would be inferred from the average sea level pressure and Earth's area of 51007.2 megahectares, this portion being displaced by Earth's mountainous terrain. Atmospheric pressure is the total weight of the air above unit area at the point where the pressure is measured. Thus air pressure varies with location and weather.
   Not all deformations originate within the Earth. The gravity of the Moon and Sun cause the Earth's surface at a given point to undulate by tenths of meters over a nearly 12-hour period (see Earth tide).
  
  Section::::Introduction.:Radius and local conditions.
  
  Given local and transient influences on surface height, the values defined below are based on a "general purpose" model, refined as globally precisely as possible within of reference ellipsoid height, and to within of mean sea level (neglecting geoid height).
   Section::::Pressure and temperature structure.:Pressure.
  
  The pressure of the atmosphere is maximum at sea level and decreases with altitude. This is because the atmosphere is very nearly in hydrostatic equilibrium so that the pressure is equal to the weight of air above a given point. The change in pressure with altitude can be equated to the density with the hydrostatic equation
  
  where:
  
  Since temperature in principle also depends on altitude, one needs a second equation to determine the pressure as a function of altitude as discussed in the next section.
  
  Section::::Pressure and temperature structure.:Temperature.
   Pure water boils at at earth's standard atmospheric pressure. The boiling point is the temperature at which the vapor pressure is equal to the atmospheric pressure around the water. Because of this, the boiling point of water is lower at lower pressure and higher at higher pressure. Cooking at high elevations, therefore, requires adjustments to recipes or pressure cooking. A rough approximation of elevation can be obtained by measuring the temperature at which water boils; in the mid-19th century, this method was used by explorers.
  
  Section::::Measurement and maps.
   As a consequence, for example, within a shell of uniform thickness and density there is "no net" gravitational acceleration anywhere within the hollow sphere.
   Pressure (P), mass (m), and the acceleration due to gravity (g), are related by P = F/A = (m*g)/A, where A is surface area. Atmospheric pressure is thus proportional to the weight per unit area of the atmospheric mass above that location.
  
  Section::::Altitude variation.
   The atmospheric pressure at Earth's sea level averages , with a scale height of about . A dry atmosphere is composed of 78.084% nitrogen, 20.946% oxygen, 0.934% argon, and trace amounts of carbon dioxide and other gaseous molecules. Water vapor content varies between 0.01% and 4% but averages about 1%. The height of the troposphere varies with latitude, ranging between at the poles to at the equator, with some variation resulting from weather and seasonal factors.
   Atmospheric pressure pressing on the surface of a liquid must be taken into account when trying to discover the "total" pressure acting on a liquid. The total pressure of a liquid, then, is "ρgh" plus the pressure of the atmosphere. When this distinction is important, the term "total pressure" is used. Otherwise, discussions of liquid pressure refer to pressure without regard to the normally ever-present atmospheric pressure.
   At about 28 miles (45 km, 150 thousand feet ) Earth altitude the pressure starts to be equivalent to Mars surface pressure. However, the major component of Mars air, CO gas, is denser than Earth air for a given pressure. Perhaps more significantly there is no land at this altitude on earth. The highest point on earth is the summit of Mount Everest at about 5.5 miles (8.8 km, 29 thousand feet), where the pressure is about fifty times greater than on the surface of Mars. The correct atmospheric pressure can be created by a vacuum chamber. NASA's Space Power Facility was used to test the airbag landing systems for the Mars Pathfinder and the Mars Exploration Rovers, Spirit and Opportunity, under simulated Mars atmospheric conditions.
   Section::::Process.
  
  The static pressure of air is the pressure in a free-flowing air stream and is depicted by isobars in weather maps. Differences in static pressure arise from global and microclimate thermal phenomena and create the air flow we call wind. Dynamic pressure is the pressure exerted when the wind comes into contact with an object such as a hill or a building and it is described by the following equation:
  
  where (using SI units):
   Section::::Mechanism.
  