The greenhouse effect

The greenhouse effect is the rise in temperature that the Earth experiences because certain gases in the atmosphere (water vapor, carbon dioxide, nitrous oxide, and methane, for example) trap energy from the sun. Without these gases, heat would escape back into space and Earth’s average temperature would be about 60ºF colder. Because of how they warm our world, these gases are referred to as greenhouse gases.

Have you ever seen a greenhouse? Most greenhouses look like a small glass house. Greenhouses are used to grow plants, especially in the winter. Greenhouses work by trapping heat from the sun. The glass panels of the greenhouse let in light but keep heat from escaping. This causes the greenhouse to heat up, much like the inside of a car parked in sunlight, and keeps the plants warm enough to live in the winter.
The Earth’s atmosphere is all around us. It is the air that we breathe. Greenhouse gases in the atmosphere behave much like the glass panes in a greenhouse. Sunlight enters the Earth's atmosphere, passing through the blanket of greenhouse gases. As it reaches the Earth's surface, land, water, and biosphere absorb the sunlight’s energy. Once absorbed, this energy is sent back into the atmosphere. Some of the energy passes back into space, but much of it remains trapped in the atmosphere by the greenhouse gases, causing our world to heat up.

The greenhouse effect is important. Without the greenhouse effect, the Earth would not be warm enough for humans to live. But if the greenhouse effect becomes stronger, it could make the Earth warmer than usual. Even a little extra warming may cause problems for humans, plants, and animals.

Further information in http://epa.gov/climatechange/kids/greenhouse.html

http://envis.tropmet.res.in/kidscorner/greenhouse.htm

Watch the video:

 

The water cycle

The Water Cycle (also known as the hydrologic cycle) is the journey water takes as it circulates from the land to the sky and back again.

The Sun's heat provides energy to evaporate water from the Earth's surface (oceans, lakes, etc.). Plants also lose water to the air (this is called transpiration). The water vapor eventually condenses, forming tiny droplets in clouds. When the clouds meet cool air over land, precipitation (rain, sleet, or snow) is triggered, and water returns to the land (or sea). Some of the precipitation soaks into the ground. Some of the underground water is trapped between rock or clay layers; this is called groundwater. But most of the water flows downhill as runoff (above ground or underground), eventually returning to the seas as slightly salty water.

To sum up:

There are six important processes that make up the water cycle.

1.      Condensation - the opposite of evaporation. Condensation occurs when a gas is changed into a liquid.

2.      Infiltration - Infiltration is an important process where rain water soaks into the ground, through the soil and underlying rock layers.

3.      Runoff - Much of the water that returns to Earth as precipitation runs off the surface of the land, and flows down hill into streams, rivers, ponds and lakes.

4.      Evaporation - the process where a liquid, in this case water, changes from its liquid state to a gaseous state.

5.      Precipitation - When the temperature and atmospheric pressure are right, the small droplets of water in clouds form larger droplets and precipitation occurs. The raindrops fall to Earth. 

6.      Transpiration - As plants absorb water from the soil, the water moves from the roots through the stems to the leaves. Once the water reaches the leaves, some of it evaporates from the leaves, adding to the amount of water vapor in the air. This process of evaporation through plant leaves is called transpiration.

More information in: http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Watercycle.shtml

Do the gap filling in: http://education.jlab.org/reading/water_cycle.html