There are several biogeochemical cycles. They all work in similar fashion in that the element or compound is released in the air and returned to the ground. The two basic cycles this section will focus on are the water cycle and the carbon cycle.
The water cycle is also known as the hydrologic cycle. It involves the movement of water in all states of matter (solid, liquid and gas) through the atmosphere and back to the Earth. As water from the surface of the ocean and other bodies of water evaporates (becomes a gas), it rises into the atmosphere. Water also evaporates into the atmosphere from the leaves of plants; this process is known as transpiration. This water vapor condenses to form clouds. When the clouds become too heavy, they release precipitation in the form of a solid (snow and ice). As the precipitation falls to the surface of the Earth, it will either stay in solid form or warm up and become a liquid (rain). Some of the water that accumulates on the surface will travel down in the form of snowmelt or surface runoff and return to the ocean via rivers and streams. The rest of the water is absorbed into the Earth’s surface and travels to the water table (a process known as infiltration). The water table serves as a reservoir and can be drawn upon through the digging of wells.
The Water Cycle
Carbon is one of the most common elements on our planet. The carbon cycle helps maintain Earth’s ecosystem. Carbon gas exchange is important in maintaining a breathable atmosphere. Carbon is released through human emissions (manufacturing) and respiration. Respiration results in the release of carbon dioxide waste products into the atmosphere; an animal’s breathing is one example. Respiration release is due to human release as well as release from decomposing plant and animal life. Carbon gathers in the atmosphere and is reabsorbed through plants (land and ocean) and soil.
The Carbon Cycle
Study this example of an ideal Test Day approach to this question about the carbon cycle.
| Question | Analysis |
|---|---|
| Which of the following is a way in which carbon is released into the atmosphere? | Step 1: Think of the ways that carbon is released into the atmosphere. |
| Step 2: It is released through respiration, decomposition, and manufacturing. | |
| Step 3: The correct answer should discuss one of those possibilities. | |
| (A) pine trees engaging in photosynthesis (B) sediment settling in the ocean(C) dead algae decomposing (D) new plants growing in a forest |
Step 4: Based on the prediction above, select answer choice (C). |
Now try one on your own.
The correct answer is (A). Water enters the atmosphere through the process of transpiration and evaporation. Transpiration specifically refers to water movement through plants. Condensation happens when water vapor condenses together to form precipitation, which then falls back the Earth as rain or snow. Seepage is the movement of water through soil.