Download EARTH`S CYCLES Our planet is constantly changing. Natural cycles

EARTH’S CYCLES
Our planet is constantly changing. Natural cycles balance and regulate Earth and its atmosphere. Human
activities can cause changes to these natural cycles.
Life on Earth is well adapted to our planet’s cycles. In our solar system, Earth is the only planet with air to
breathe, liquid water to drink, and temperatures that are just right for life as we know it. Because our
existence depends on our planet and its climate, we need to understand how what we do affects the Earth.
Scientists try to figure out how our planet works by studying Earth’s cycles. Changes to Earth’s cycles can
cause changes in the climates of our planet. The more we know about these cycles, the more we will
understand how humans are affecting them and how that might change the planet.
The Energy Balance
Earth gets all its energy from the Sun and loses
energy into space If more energy is lost into
space than is received from the Sun, the planet
gets cooler. If it loses less energy than it receives,
the planet will warm up.
Have you noticed that it is often cooler when
there are clouds in the sky? Some types of clouds
act like giant sun umbrellas, shading the Earth
and reflecting the sunlight that hits them. Other
types of clouds act like a jacket, holding the heat
in and preventing it from leaving the atmosphere.
Today, most clouds act more like a sun umbrella
and help keep our climate cool. However, this
could change if global warming affects the type of
clouds, their thickness, and how much water or ice they contain.
While it might be quite warm in the countryside on a summer day, it can get unbearably hot in a nearby city!
That’s because the buildings and pavement in cities absorb oodles of sunlight, much more than the
countryside. These cities are called “heat islands.” The countryside is also cooled by water evaporating from
lakes and given off by the plants in forests and fields. Cities have fewer plants and bodies of water and so are
not cooled very much by evaporation.
The Water Cycle
Water plays many different roles on the
Earth. Some is at the poles in ice caps,
and some is in the snow and glaciers at
the tops of high mountains. Some is in
lakes and streams, and some is
underground. Some is vapor in the
atmosphere. But most of the water on
Earth is in the oceans.
Water is always on the move! The Sun’s
energy causes water to evaporate from
oceans and lakes into the atmosphere.
Plants and animals also release water
vapor into the atmosphere as they
breathe. When the atmosphere cools,
water vapor condenses; making clouds
that might produce rain or snow. Water
has been recycled in its different forms as ice, liquid, or vapor --for more than 3.5 billion years.
The Active Atmosphere
Has Earth’s atmosphere ruffled your hair, blown your
homework down the street, or turned your umbrella
inside out? The atmosphere, a thin blanket of gases that
surrounds Earth, transports heat and water and filters out
deadly ultraviolet radiation. Whether it is just a gentle
breeze or a hurricane-force gale, Earth’s atmosphere is
constantly on the move.
When the atmosphere moves, it evens out differences in
temperature between the chilly poles and the warm
equator. Warm air from the equator moves toward the
poles and cold air from the poles moves toward the
equator. This circulation of air is disrupted a bit by the
Earth’s rotation. This makes counterclockwise winds
around hurricanes, winter storms, tornadoes, and other
low-pressure areas north of the equator and clockwise
south of the equator.
The Ocean in Motion
The ocean water is in motion because of
differences in temperature and saltiness.
Water that is warmed at the sea surface near
the equator moves toward the chilly poles.
Cold, salty currents flow into the deepest parts
of the sea.
Oceans can hold a large amount of heat energy
– much more than the atmosphere. In the past
few decades, Earth’s oceans have become
warmer. Even as far as 2 miles (3.2 kilometers)
below the surface of the sea, the ocean water
has been warmed. Scientists estimate the
oceans may have absorbed up to half of the
energy trapped by greenhouse gases over the
last century.
The Carbon Cycle
All living things are made of carbon.
Carbon is also a part of the ocean, air, and
even rocks. Because the Earth is a dynamic
place, carbon does not stay still. It is on the
move!
In the atmosphere, carbon is attached to
some oxygen in a gas called carbon
dioxide.
Plants use carbon dioxide and sunlight to
make their own food and grow. The carbon
becomes part of the plant. Plants that die
and are buried may turn into fossil fuels
made of carbon like coal and oil over
millions of years. When humans burn fossil
fuels, most of the carbon quickly enters
the atmosphere as carbon dioxide.
Carbon dioxide is a greenhouse gas and
traps heat in the atmosphere. Without it and other greenhouse gases, Earth would be a frozen world. But
humans have burned so much fuel that there is about 30% more carbon dioxide in the air today than there
was about 150 years ago, and Earth is becoming a warmer place. In fact, ice cores show us that there is now
more carbon dioxide in the atmosphere than there has been in the last 420,000 years.
The Nitrogen Cycle
Take a deep breath. Most of what you just
inhaled is nitrogen. In fact, 80% of the air in
our atmosphere is made of nitrogen. Your
body does not use the nitrogen that you
inhale with each breath. But, like all living
things, your body needs nitrogen. Your body
gets the nitrogen it needs to grow from food.
Most plants get the nitrogen they need from
soil. Many farmers use fertilizers to add
nitrogen to the soil to help plants grow larger
and faster. Both nitrogen fertilizers and
forest fires add huge amounts of nitrogen
into the soil and nearby lakes and rivers.
Water full of nitrogen causes plants and algae
to grow very fast and then die all at once
when there are too many for the
environment to support.
The Rock Cycle
Over many thousands of years, energy from
the Sun moves the wind and water at the
Earth’s surface with enough force to break
rocks apart into sand and other types of
sediment. When sediment is buried and
cemented together, it becomes a
sedimentary rock such as sandstone or
shale.
If rocks are buried very deeply, they are in
an environment that is very hot and has high
pressure. The crystals and texture of the
rocks change as they turn into metamorphic
rocks like marble or slate. If, deep
underground, rocks are put under too much
pressure and temperatures that are too hot,
they will melt, forming molten rock called magma. Sometimes magma cools and forms igneous rock deep
underground. Other times magma flows to the Earth’s surface and erupts from a volcano.
Rocks can affect the atmosphere! Erupting volcanoes send tiny particles of ash and gases into the atmosphere.
Tiny particles of ash help make raindrops in the atmosphere as water condenses around them. The gases
released from volcanoes can become sulfuric acid droplets that screen out sunlight. Large volcanic eruptions
can even reduce Earth’s temperature for months or several years.