The document describes the four major spheres that make up Earth: the hydrosphere (water portion), atmosphere (gaseous envelope of air), geosphere (layer under the atmosphere and oceans composed of the core, mantle, and crust), and biosphere (all life on Earth within the solid Earth, hydrosphere, and atmosphere). It also defines the three main parts of the solid Earth as the core, mantle, and crust, and identifies plate tectonics as the model that explains the positions of continents and the occurrence of volcanoes and earthquakes.

1. A view of Earth 1.2

2. Hydrosphere The water portion of Earth; one of the traditional subdivisions of Earth’s physical environment.

3. Atmosphere The gaseous portion of the planet; the planet’s envelop of air; one of the traditional subdivisions of Earth’s physical environment.

4. Geosphere Layer of Earth under both the atmosphere and the oceans; it is composed of the core, the mantle, and the crust.

5. Biosphere All life on Earth; the parts of the solid Earth, hydrosphere, and atmosphere in which living organisms can be found.

6. Core The innermost layer of Earth, located beneath the mantle; the core is divided into an outer core and an inner core.

7. Mantle The 2890-Kilometer-thick layer of Earth located below the crust.

8. Crust Thin, rocky outer layer of Earth.

9. Key Concept What are the four major spheres into which Earth is divided? Earth can be thought of as consisting of four major sphere: the hydrosphere, atmosphere, geosphere, and biosphere.

10. Key Concept What defines the three main parts of the solid Earth? Because the geosphere is not uniform, it is divided into three main parts based on differences in composition- the core, the mantle, and the crust.

11. Key Concept Which model explains the position of continents and the occurrence of volcanoes and earthquakes? The theory that finally emerged, called plates tectonics, provided geologists with a model to explain how earthquakes and volcanic eruptions occur and how continents move.