Structure of the Earth

The interior structure of the Earth is layered in spherical shells, like an onion. These layers can be defined by either their chemical or their rheological properties. Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. Scientific understanding of the internal structure of the Earth is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanoes or volcanic activity, analysis of the seismic waves that pass through the Earth, measurements of the gravitational and magnetic fields of the Earth, and experiments with crystalline solids at pressures and temperatures characteristic of the Earth's deep interior.

Mass

The force exerted by Earth's gravity can be used to calculate its mass, and by estimating the volume of the Earth, its average density can be calculated. Astronomers can also calculate Earth's mass from its orbit and effects on nearby planetary bodies.

Down

Down may refer to:

Music

Songs

Earth

Earth /ˈɜːrθ/ (also the world, in Greek: Γαῖα Gaia, or in Latin: Terra) is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to harbor life.

According to evidence from radiometric dating and other sources, Earth was formed about 4.54 billion years ago. Earth gravitationally interacts with other objects in space, especially the Sun and the Moon. During one orbit around the Sun, Earth rotates about its own axis 366.26 times, creating 365.26 solar days or one sidereal year. Earth's axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). The Moon is Earth's only permanent natural satellite. Its gravitational interaction with Earth causes ocean tides, stabilizes the orientation of Earth's rotational axis, and gradually slows Earth's rotational rate.

Core

Core may refer to:

Computers and technology

To the Earth

To the Earth is a light gun shooter for the Nintendo Entertainment System. It was released on November 1989 in North America and in Europe on February 23, 1990. It uses the NES Zapper to destroy ships and gain powerups. The game requires quick reflexes and good aiming due to the enemy space crafts being very agile and quite difficult to shoot.

Gameplay

The object of the game is to destroy incoming enemy spacecraft, bombs, missiles, asteroids, etc. without destroying friendly vessels. Due to the very quick speeds of the enemy ships and asteroids, the game is considered to be one of the most challenging Zapper games for the NES. The shield of the spacecraft players are in command of constantly goes down each time they shoot at an enemy and miss. Players also can use a powerful bomb to destroy everything on screen, shoot a comet power-up that grants temporary protection from a limited number of hits, as well as a shield-repairing item dropped off by a friendly spacecraft. Game bosses are fought at the end of each level as the player moves through the Solar system. When the player reaches the Earth level, the player must battle and destroy the final boss, who is an alien named Nemesis. The goal is to retrieve vials of medicine and deliver them to the Earth while preventing Nemesis from passing through the planet's atmosphere.