GEF

Unit 4   |  The Global Ecosystem 92 2. In the hydrosphere, carbon is dissolved in water. The oceans are the largest reservoir of carbon on the planet. Marine organisms such as clams and snails use calcium to make shells. After these organisms die, the calcium carbon- ate in their shells eventually settles to the ocean floor and becomes limestone rock, part of the lithosphere. 3. Carbon moves into the biosphere through plants both on land and in the oceans in the form of phytoplankton . Plants absorb carbon from the atmosphere or water during photosynthesis , the process of creating energy from CO 2 , water, and sunlight. When plants die, they become buried in layers of soil and clay over time, and turn into part of the lithosphere. Over millions of years, heat and pressure of the Earth’s crust transforms the carbon from these organisms into oil and coal deposits known as fossil fuels. 4. Humans drill and mine for fossil fuels, and use them to make electricity and to power cars and machinery, releas- ing CO 2 to the atmosphere once again. 4.3  The Water Cycle and the Nitrogen Cycle The water cycle, or hydrological cycle, also illustrates the inter- dependence of Earth systems and human activity. 1. The hydrosphere system includes how water moves on our planet. Water is found in liquid form in lakes, rivers, groundwater, and oceans. Water that has contact with air is evaporated through the energy of sunlight and wind, changing water from liquid into water vapor. 2. Water vapor becomes a part of the atmosphere system. These water vapor molecules condense to form clouds. When conditions are right, water falls as precipitation in the form of rain, snow, sleet, or hail. PHYTOPLANKTON Tiny photosynthesizing organisms that inhabit the upper layers of the ocean where sunlight is able to penetrate; they are integral to the carbon and oxygen cycles of planet Earth. PHOTOSYNTHESIS The production of car- bohydrates from carbon dioxide and hydrogen in the chlorophyll-containing tis- sues of plants in the presence of light.