2.3 Biogeochemical Cycles of the Green World (Planet Earth)
35
patterns. The water cycle plays a crucial role in the sustenance of life on Earth and
has six major steps:
• Step 1: Evaporation
• Step 2: Condensation
• Step 3: Sublimation
• Step 4: Precipitation
• Step 5: Transpiration
• Step 6: Runoff
• Step 7: Infiltration
2.3.1.1 Step 1: Evaporation
Water can be found in plants, lakes, oceans, soil, and swamps. Heat from the sun
excites the water molecules causing them to spread out. Evaporation is mainly
defined as the loss of density and causes water to form water vapor clouds in the air
(Barry and Chorley 2009). Water evaporation usually happens when water reaches
its boiling point, which is about 100 ◦ C. Contrarily, in places where humidity and
air pressure are lower, less heat energy is required for evaporating water due to the
lower pressure holding the water molecules. Water evaporating from oceans is nonsalty as the salt is too heavy for it to rise along with the vapor. This is the reason
water found in lakes and rivers is not salty. Ice and snow can become water vapor
without necessarily turning into water. The process is referred to as “sublimation”
and is attributed to dry winds and low humidity. Sublimation happens typically at
mountain peaks where there is low air pressure, thus implying that less energy is
required for sublimating the ice into vapor. Mountain Everest is among the highest
peaks on the planet with the necessary components for sublimation.
What is the role of evaporation in availing water in water bodies? Is it a
positive or negative thing?
2.3.1.2 Step 2: Condensation
Water vapor that rises into the atmosphere cools when it meets the cooler air found
higher in the sky. Consequently, the vapor becomes a cloud that winds and moving
air currents push around the world. The water vapor starts condensing on the surface
of tiny particles that have escaped during the evaporation process. The tiny droplets
begin falling into each other and merge to produce a larger droplet. Gravity pulls
down a droplet that is large enough at a rate that is more than the force in the cloud,
resulting in rainfall or precipitation (Barry and Chorley 2009). In case precipitation
happens within conditions that are specifically cold or with low air pressure, such
water droplets can usually crystallize and freeze, making a waterfall in the form of
solid ice or snow.
35
patterns. The water cycle plays a crucial role in the sustenance of life on Earth and
has six major steps:
• Step 1: Evaporation
• Step 2: Condensation
• Step 3: Sublimation
• Step 4: Precipitation
• Step 5: Transpiration
• Step 6: Runoff
• Step 7: Infiltration
2.3.1.1 Step 1: Evaporation
Water can be found in plants, lakes, oceans, soil, and swamps. Heat from the sun
excites the water molecules causing them to spread out. Evaporation is mainly
defined as the loss of density and causes water to form water vapor clouds in the air
(Barry and Chorley 2009). Water evaporation usually happens when water reaches
its boiling point, which is about 100 ◦ C. Contrarily, in places where humidity and
air pressure are lower, less heat energy is required for evaporating water due to the
lower pressure holding the water molecules. Water evaporating from oceans is nonsalty as the salt is too heavy for it to rise along with the vapor. This is the reason
water found in lakes and rivers is not salty. Ice and snow can become water vapor
without necessarily turning into water. The process is referred to as “sublimation”
and is attributed to dry winds and low humidity. Sublimation happens typically at
mountain peaks where there is low air pressure, thus implying that less energy is
required for sublimating the ice into vapor. Mountain Everest is among the highest
peaks on the planet with the necessary components for sublimation.
What is the role of evaporation in availing water in water bodies? Is it a
positive or negative thing?
2.3.1.2 Step 2: Condensation
Water vapor that rises into the atmosphere cools when it meets the cooler air found
higher in the sky. Consequently, the vapor becomes a cloud that winds and moving
air currents push around the world. The water vapor starts condensing on the surface
of tiny particles that have escaped during the evaporation process. The tiny droplets
begin falling into each other and merge to produce a larger droplet. Gravity pulls
down a droplet that is large enough at a rate that is more than the force in the cloud,
resulting in rainfall or precipitation (Barry and Chorley 2009). In case precipitation
happens within conditions that are specifically cold or with low air pressure, such
water droplets can usually crystallize and freeze, making a waterfall in the form of
solid ice or snow.