Earth's Water

In the first lesson, students build on their knowledge of Earth’s systems by focusing on the phenomena interacting in Earth’s hydrosphere and the distribution of water around the planet. They use that knowledge to analyze how fresh water moves and becomes salty.

• Earth has water and that water is found in different reservoirs around the planet, including the ocean, rivers, lakes, groundwater, glaciers, and the atmosphere. 
• All water found on Earth forms a system called the hydrosphere because it is made up of interacting parts, including frozen ice of glaciers and ice caps, water vapor in the atmosphere, salt water of the oceans, and fresh water in various reservoirs such as lakes and rivers. 
• Water is cycled throughout the planet because of heat from the sun. 
• The movement of water on the planet connects all of Earth’s systems because it interacts with and influences all of the systems (hydrosphere, atmosphere, biosphere, and geosphere). 
• Oceans become salty because of interactions between different Earth systems. 
• Most of the water on Earth is found in the oceans. Oceans cover 71 percent of Earth’s surface and contain almost 97 percent of the world’s total water. 
  
  

• Why are oceans important to understand when talking about water on Earth?
• How is ocean water different from other water on Earth?
• What is the proportion of freshwater on Earth and where it is found?
• How does the cycling of water between states cause Earth’s atmosphere to interact with the hydrosphere?
• How does the water cycle demonstrate that air is matter because it is made up of particles too small to be seen?
• How can chemical weathering on Earth’s surface be caused by interactions among the hydrosphere, the atmosphere, and the geosphere?
  
  

Misconception: The equator is warmer than the poles because it is closer to the sun.

Fact: The equator is warmer because it receives the most direct sunlight while the poles receive indirect sunlight.

Misconception: Science and engineering are completely separate from each other.

Fact: Science and engineering are connected. Engineers use knowledge gained from scientists to design technologies that solve problems. Scientists can then use those technologies to ask deeper questions.

Conservation :  the weighing of human needs against the needs of the environment to create a sustainable way for humans to live off of natural resources

Environmental Threat :  anything that can cause harm to the environment (e.g., pollution, deforestation, invasive species, overhunting, and climate change)

Evaporation :  the process of liquid water changing into water vapor, its gas state

Ocean Currents :  paths of flowing ocean water that push warm and cold water to different parts of the planet

Precipitation :  the process of water falling back to Earth in the form of rain, snow, sleet, or hail

Proportion :  the relationship between things, as to size, quantity, or number

Runoff :  occurs when water, along with the substances carried in it, flow from the surface of an area of land, a building or structure

Water Cycle : the circulation of water through the hydrosphere from Earth’s surface to the atmosphere and back

Weather :  the conditions of the atmosphere (temperature, humidity, wind speed, air pressure, and precipitation) in a particular place at a particular time

Message in a Bottle

In August 2015, scientists in England received a surprise in the mail. It was a postcard that had spent the last 109 years in a bottle, traveling the world’s oceans. This postcard is the oldest message in a bottle that has ever been found.

The postcard had a note written on it. It promised a shilling to anyone who returned it to the Marine Biological Association of the UK. A shilling is a former British coin.

The postcard in the bottle was sent out because scientists wanted to understand where ocean water moved around the planet. For centuries, people have dropped messages in bottles to study the movements of ocean currents. Ocean currents are the paths of flowing ocean water that push warm and cold water to different parts of the planet.

Ocean currents are constantly moving water around the planet. The movement of ocean currents is complex. It is affected by Earth’s rotation on its axis, how much salt the water holds, the temperature of the water, land formations on the ocean floor, and wind

Because of this, ocean currents involve interactions of different Earth systems: the hydrosphere (all of the water on Earth), the geosphere (Earth’s landforms, including rocks and soil), and the atmosphere (the mixture of gasses, dust, water vapor, and other molecules above Earth’s crust).

The postcard in the bottle was found on a beach in Germany. It was one of 1,000 bottles released in the North Sea between 1904 and 1906. Slightly more than half of the bottles were returned to the scientists. The rest were believed to be lost at sea.

It has been so long since the bottles were put into the ocean that the United Kingdom no longer makes shillings. The Marine Biological Association had to find a shilling on eBay after they received the postcard in 2015.

Scientists continue to study ocean currents today. However, they now use different technologies. For example, scientists sometimes attach tiny electronic tags on fish that track where they have been.

Oceans on Earth

Earth is a water planet. Oceans cover about 71 percent of Earth’s surface. There are five oceans on Earth: the Arctic Ocean, the Atlantic Ocean, the Indian Ocean, the Pacific Ocean, and the Southern Ocean. However, water flows between these oceans because they are not actually separated. Instead, they form one massive body of water. This is why scientists have used messages in bottles. The currents carry the bottles on their journey around the planet.

Oceans get very deep. The average depth of the ocean is 3,688 meters (12,100 feet). In fact, the planet’s longest mountain range runs through the middle of the ocean. It is called the Mid-Oceanic Ridge, and it is found at a divergent tectonic plate boundary. This mountain range covers 65,000 km (40,389 miles). The average depth to the top of the ridge is 2,500 meters (8,202 feet).

The Water Cycle

With enough energy from the sun, liquid water on Earth’s surface evaporates into the atmosphere. Evaporation is the process of liquid water changing into water vapor, its gas state. As the water vapor moves higher in the atmosphere, it loses heat. Eventually it will condense. When it condenses, it changes from a gas back into liquid water. Precipitation is water falling back to Earth’s surface in the form of rain, snow, sleet, or hail.

Some of the water that doesn’t immediately evaporate back into the atmosphere will collect into lakes, pools, and other water sources. Some water will seep underground. Water that doesn’t seep into the ground or get absorbed by plants and animals flows downhill because of gravity. Any area of land where all of the water that falls in it drains into a common outlet is called a watershed.

Plants absorb some water through their roots and release it through their leaves as water vapor back to the atmosphere. The process by which water moves through plants from roots to their leaves and into the atmosphere is called transpiration.

The circulation of water from a collection to the atmosphere and back to the surface is called the water cycle.

For the hands-on activity in this lesson, students explore the distribution of freshwater and saltwater on Earth and figure out how to use the water distribution model and salt water model they create to explain the phenomena of system interactions that result in fresh water entering salty oceans.