Earth's Water

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.