Major Understandings:

1.1a Earth's Sun is an average-sized star. The Sun is more than a million times greater

in volume than Earth.

1.1b Other stars are like the Sun but are so far away that they look like points of light.

Distances between stars are vast compared to distances within our solar system.

1.1c The Sun and the planets that revolve around it are the major bodies in the solar system.

Other members include comets, moons, and asteroids. Earth's orbit is nearly circular.

1.1d Gravity is the force that keeps planets in orbit around the Sun and the Moon in

orbit around the Earth.

1.1e Most objects in the solar system have a regular and predictable motion. These

motions explain such phenomena as a day, a year, phases of the Moon, eclipses, tides,

meteor showers, and comets.

1.1f The latitude/longitude coordinate system and our system of time are based on

celestial observations.

1.1g Moons are seen by reflected light. Our Moon orbits Earth, while Earth orbits the

Sun. The Moon's phases as observed from Earth are the result of seeing different portions

of the lighted area of the Moon's surface. The phases repeat in a cyclic pattern in

about one month.

1.1h The apparent motions of the Sun, Moon, planets, and stars across the sky can be

explained by Earth's rotation and revolution. Earth's rotation causes the length of one

day to be approximately 24 hours. This rotation also causes the Sun and Moon to appear

to rise along the eastern horizon and to set along the western horizon. Earth's revolution

around the Sun defines the length of the year as 365 1/4 days.

1.1i The tilt of Earth's axis of rotation and the revolution of Earth around the Sun cause

seasons on Earth. The length of daylight varies depending on latitude and season.

1.1j The shape of Earth, the other planets, and stars is nearly spherical.

Major Understandings:

2.1a Nearly all the atmosphere is confined to a thin shell surrounding Earth. The atmosphere

is a mixture of gases, including nitrogen and oxygen with small amounts of water

vapor, carbon dioxide, and other trace gases. The atmosphere is stratified into layers,

each having distinct properties. Nearly all weather occurs in the lowest layer of the

atmosphere.

2.1b As altitude increases, air pressure decreases.

2.1c The rock at Earth's surface forms a nearly continuous shell around Earth called the

lithosphere.

2.1d The majority of the lithosphere is covered by a relatively thin layer of water called

the hydrosphere.

2.1e Rocks are composed of minerals. Only a few rock-forming minerals make up most

of the rocks of Earth. Minerals are identified on the basis of physical properties such as

streak, hardness, and reaction to acid.

2.1f Fossils are usually found in sedimentary rocks. Fossils can be used to study past

climates and environments.

2.1g The dynamic processes that wear away Earth's surface include weathering and

erosion.

2.1h The process of weathering breaks down rocks to form sediment. Soil consists of

sediment, organic material, water, and air.

2.1i Erosion is the transport of sediment. Gravity is the driving force behind erosion.

Gravity can act directly or through agents such as moving water, wind, and glaciers.

2.1j Water circulates through the atmosphere, lithosphere, and hydrosphere in what is

known as the water cycle.

Major Understandings:

2.2a The interior of Earth is hot. Heat flow and movement of material within Earth

cause sections of Earth's crust to move. This may result in earthquakes, volcanic

eruption, and the creation of mountains and ocean basins.

2.2b Analysis of earthquake wave data (vibrational disturbances) leads to the conclusion

that there are layers within Earth. These layers in the crust, mantle, outer core, and

inner core have distinct properties.

2.2c Folded, tilted, faulted, and displaced rock layers suggest past crustal movement.

2.2d Continents fitting together like puzzle parts and fossil correlations provided initial

evidence that continents were once together.

2.2e The Theory of Plate Tectonics explains how the solid lithosphere consists of a

series of plates that float on the partially molten section of the mantle. Convection

cells within the mantle may be the driving force for the movement of the plates.

2.2f Plates may collide, move apart, or slide past one another. Most volcanic activity

and mountain building occur at the boundaries of these plates, often resulting in earthquakes.

2.2g Rocks are classified according to their method of formation. The three classes of

rocks are sedimentary, metamorphic, and igneous. Most rocks show characteristics that

give clues to their formation conditions.

2.2h The rock cycle model shows how types of rock or rock material may be transformed

from one type of rock to another.

2.2i Weather describes the conditions of the atmosphere at a given location for a short

period of time.

2.2j Climate is the characteristic weather that prevails from season to season and year

to year.

2.2k The uneven heating of Earth's surface is the cause of weather.

2.2l Air masses form when air remains nearly stationary over a large section of Earth's

surface and takes on the conditions of temperature and humidity from that location.

Weather conditions at a location are determined primarily by temperature, humidity,

and pressure of air masses over that location.

2.2m Most local weather condition changes are caused by movement of air masses.

2.2n The movement of air masses is determined by prevailing winds and upper air currents.

2.2o Fronts are boundaries between air masses. Precipitation is likely to occur at these

boundaries.

2.2p High-pressure systems generally bring fair weather. Low-pressure systems usually

bring cloudy, unstable conditions. The general movement of highs and lows is from

west to east across the United States.

2.2q Hazardous weather conditions include thunderstorms, tornadoes, hurricanes, ice

storms, and blizzards. Humans can prepare for and respond to these conditions if given

sufficient warning.

2.2r Substances enter the atmosphere naturally and from human activity. Some of these

substances include dust from volcanic eruptions and greenhouse gases such as carbon

dioxide, methane, and water vapor. These substances can affect weather, climate, and

living things.