Properties of Water

the nitrogen cycle

The Nitrogen Cycle

The element Nitrogen also has the ability to cycle globally, because of its presence in the atmosphere. Nitrogen in the atmosphere is only found in the form N2. Only very few creatures can take in nitrogen in this form. Therefore, nitrogen-fixing bacteria in the soil take on the task. The bacteria come in two types: free bacteria and root nodule bacteria. Free bacteria survive on their own in the soil. These bacteria carry out the chemical reaction that changes N2 to ammonium (NH4+), called Nitrogen Fixation. Ammonium and nitrate (NO3-), another form of nitrogen, can be used by most plants and are found in Amino Acids. Nitrates come from nitrifying bacteria in the soil, which take in ammonium to create nitrates (called nitrification). These nitrates, in addition to supplying Amino Acids to plants, return to the atmospheric reservoir through a process called, incidentally, denitrification. Finally we get to root nodule bacteria. These bacteria supply legumes, or pod-producing plants, with nitrogen that they cannot recieve on their own. This is a commensalistic relationship, because the bacteria do not benefit, but the legumes could not possibly survive without them. Another process in the Nitrogen Cycle is the decomposition of animals. As stated before, animals cannot absorb N2 on their own, so they must rely on the plants they eat (or lower level consumers) to get nitrogen. When these animals die, the nitrogen stays within them, as does Carbon, and detritovores transform it into ammonium, thus continuing the cycle.

Abiotic reservoirs: atmosphere, soil
Biotic reservoirs: animals, plants, detritivores, bacteria

The Layers of the Atmosphere

 

The layers of the Atmosphere 

TROPOSPHERE

This is the layer of the atmosphere closest to the Earth's surface, extending up to about 10-15 km above the Earth's surface. It contains 75% of the atmosphere's mass. The troposphere is wider at the equator than at the poles. Temperature and pressure drops as you go higher up the troposphere 

STRATOSPHERE

This layer lies directly above the troposphere and is about 35 km deep. It extends from about 15 to 50 km above the Earth's surface. The lower portion of the stratosphere has a nearly constant temperature with height but in the upper portion the temperature increases with altitude because of absorption of sunlight by ozone. This temperature increase with altitude is the opposite of the situation in the troposphere.

MESOSPHERE

Directly above the stratosphere, extending from 50 to 80 km above the Earth's surface, the mesosphere is a cold layer where the temperature generally decreases with increasing altitude. Here in the mesosphere, the atmosphere is very rarefied nevertheless thick enough to slow down meteors hurtling into the atmosphere, where they burn up, leaving fiery trails in the night sky.

THERMOSPHERE

The thermosphere extends from 80 km above the Earth's surface to outer space. The temperature is hot and may be as high as thousands of degrees as the few molecules that are present in the thermosphere receive extraordinary large amounts of energy from the Sun. However, the thermosphere would actually feel very cold to us because of the probability that these few molecules will hit our skin and transfer enough energy to cause appreciable heat is extremely low.