All living things on Earth are found on or near the solid outer layer of the planet's crust, called the lithosphere. The hydrosphere, a layer of oceans, rivers and lakes, covers 75% of the lithosphere. Compared to the size of the Earth, the lithosphere is only a thin layer, several kilometers deep at most. The layer of air around the Earth is called the atmosphere. The water cycle describes how water travels through the atmosphere, hydrosphere and lithosphere. All living things need water; without the water cycle, life as we know it would not exist.
Living things also need energy to survive. That energy comes from the sun as radiant energy. It falls first on the atmosphere, then on the hydrosphere and lithosphere. But it's not absorbed evenly over the entire Earth's surface, which causes different conditions in the atmosphere at different places. The climate in the Amazon rainforest is very different from the climate at the North Pole. We refer to the areas affected by these varying conditions of the atmosphere as different climate regions.
Climate regions are the result of
A
living things existing only on the lithosphere.
B
the thickness of the lithosphere.
C
how water travels through the atmosphere, hydrosphere and lithosphere.
D
sunlight being absorbed unevenly across the Earth.
D
C
A
C
C
B
All weather takes place in the atmosphere, mostly in its very lowest layer.
Weather is the condition of the atmosphere in one place for a short period of time. To describe the weather, we look at the general conditions of the sky overhead. Is it clear, cloudy or filled with rain? We also measure six qualities of the atmosphere: precipitation, pressure, humidity, temperature, wind and air quality.
Pressure is the force of the air pushing down upon the Earth. Air pressure is measured with a tool called a barometer, so it is also known as barometric pressure. Low pressure usually brings precipitation, while high pressure often brings dry weather. Humidity is the amount of water vapor in the air compared to how much water vapor the air can hold. Temperature is a measure of heat energy. If the temperature is high, there is more energy and we feel warm. If it's low, there's less energy, so we feel cold. Wind is the direction and speed of the air moving around us. The air quality depends on the place from which it moves: it might be humid, cold, or polluted air.
If you hear a weather report say that a low pressure system is coming in, what kind of weather can you expect?
A
wind
B
polluted air
C
precipitation
D
heat
The atmosphere has four layers. The lowest layer, the troposphere, contains 90% of our air. It is where most weather and human activity occurs.
Above the troposphere is the stratosphere, where the air is thin and cold. The only time we visit the stratosphere is in a jet plane. The stratosphere includes a thin layer of a gas called ozone. This ozone layer absorbs ultraviolet radiation from space and protects all living things in the troposphere below.
The mesosphere is above the stratosphere. It is the coldest layer because its air is so thin.
The few remaining air molecules in the thermosphere, the uppermost layer, absorb radiation from the sun, protecting the layers below. Specifically, nitrogen and oxygen atoms absorb this solar radiation and release electrically charged particles called ions. Within the thermosphere, these ions are found in a layer called the ionosphere. Sometimes radio waves bounce off the ionosphere, allowing us to hear radio stations from around the world. Near the Earth's two poles these ions emit beautiful shimmering lights called auroras.
In order from bottom to top, the layers of the atmosphere are
A
troposphere, stratosphere, mesosphere, thermosphere.
B
thermosphere, mesosphere, troposphere, stratosphere.
C
stratosphere, troposphere, mesosphere, thermosphere.
D
mesosphere, stratosphere, thermosphere, troposphere.
An air mass is a large body of air with similar pressure, temperature and humidity conditions. The weather changes when a different air mass moves over us. In some places at some times, air masses move quickly and often, causing the weather to change almost daily. In other places and times, air masses stay in one spot, causing the same weather for weeks or months in a row.
Air masses can be cold or warm, wet or dry based on where they form. They don't mix when they come in contact with each other because the air is always of varying densities. So a warm air mass will move above a cooler air mass, probably causing precipitation and storms. We call the edge of an air mass where it meets another a front or weather front.
Climate is the normal weather for a given place over a long period of time. Climates are based on the kinds of air masses usually found there.
Which of these is a description of a climate?
A
a heavy snowstorm
B
a cold air mass
C
mild summers and warm winters
D
partly cloudy with a chance of rain
Because warm air is lighter, it rises while cold air moves down to take the warm air's place. This circular movement of air is called a convection current. Where the air rises, there's higher air pressure; where it falls, the pressure is low. Since cooling air can't hold as much water vapor as warm air can, the result may be rain, whether as a simple summer thunderstorm or a big hurricane.
A cyclone is a weather system where the air rushes into a low-pressure area, and winds rotate inward in a counterclockwise direction. Cyclones can be very powerful and destructive. A tornado is a very intense, small cyclone. As the very fast winds spiral inward and upward they can pick up large objects like trees, trucks and even rooftops.
The most powerful storms of all are called hurricanes (in Asia they are called typhoons). These huge cyclones can cover hundreds of square miles. Formed over warm tropical oceans, hurricanes can have winds of more than 125 miles per hour. These storms can cause incredible damage due to floods, waves, rain, and wind.
Hurricanes are
A
not created by air masses.
B
formed over arctic oceans.
C
a kind of cyclone.
D
less powerful than tornadoes.