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13 |
EARTH AS A SYSTEM: ENERGY, MATTER AND LIFE |
- Life on Earth depends on the flow of energy and matter, mainly
driven by the Sun, Earth’s interior heat, and chemical reactions in air, water,
and rocks.
- The Earth system is made up of interacting 'spheres' -
· Geosphere: Solid rocks, soil, landforms (E.g. Deccan
plateau & Thar desert), and the Earth's interior.
· Hydrosphere: Liquid water in the form of surface water like
oceans, rivers, lakes and groundwater.
· Cryosphere: Solid water (ice, snow). E.g. Himalayan
glaciers, snow in Ladakh and polar ice caps.
· Atmosphere: The air surrounding the Earth (cleaner air in
the mountains and forests).
· Biosphere: All living organisms and their habitats (mangroves, forests, farms, plankton, coral reefs
etc.).
- Natural processes, such as heating by solar radiation, air and
water movements, and nutrient cycling connect these spheres in a delicate
balance.
- A disturbance in one sphere can affect others. E.g.
o Less snowfall in winters →
less water in the lake in summers → less water to support growth of grass.
o Warmer Arabian Sea water →
more evaporation → fluctuations
in southwest monsoon → floods
and droughts → disrupt the
hydrosphere.
o High atmospheric temperatures → glacier & polar ice melting in cryosphere → sea-level rise → flooding of low-lying areas and
habitat loss in the biosphere.
UNEVEN HEATING OF THE EARTH
- Solar radiation is the main source of energy. It reaches
the Earth as electromagnetic (EM) waves that travel through a vacuum at
the speed of light (3 × 10⁸ m s⁻¹).
- EM waves range from high
frequency, short wavelength radiation (gamma rays and X-rays)
to low frequency, long wavelength radiation (infrared and radio waves).
- The high frequency EM waves have very high energy. It is harmful
for life.
- The entire range of electromagnetic radiation is called the electromagnetic
spectrum.
Electromagnetic spectrum
- About 99% of solar radiation reaching Earth lies in the ultraviolet
(UV), visible, and infrared (IR) regions of the spectrum, which
shape climate and support life.
- Gamma rays & X-rays are mostly filtered by the upper
atmosphere, while microwaves and radio waves carry very little energy to
significantly warm Earth.
- Visible light provides energy for photosynthesis. It also
partly warms the land and water.
- Infrared radiation warms Earth's surface, which then
re-radiates heat into the atmosphere. Some of this heat is trapped by greenhouse
gases (CO₂, CH₄ & water vapour) keeping Earth warm to support life.
Ready to Go Beyond
·
UV rays (wavelength range 100–400 nm) have higher
energy than visible light.
·
Excess exposure to UV can damage eyes and skin and
increase cancer risk. So, protective glasses and sunscreen are recommended. UV
rays are also used in water purification and fluorescent lights.
- The amount of the solar radiation that reaches the Earth's
surface is called insolation. It is responsible for warming the Earth's
surface and atmosphere.
- The average solar energy received per unit time per unit area
perpendicular to the Sun's rays at the top of the Earth's atmosphere is called
the solar constant.
Its
value is about 1.4 kilowatts/m² (1.4
kW m⁻²) or
1400 joules/s/m²
(1400 J s⁻¹ m⁻²)
- It represents the Sun’s energy reaching Earth before atmospheric
absorption, scattering, or reflection.
- The solar constant helps understand the Earth's energy balance,
climate and weather patterns.
- Some solar energy is absorbed and scattered by gases, clouds,
and dust before reaching Earth’s surface. Hence, maximum insolation is lower
than the solar constant and is about 1 kW m⁻² under clear sky.
- India’s geographical location is in the tropical and
sub-tropical regions. So, it receives abundant sunlight making solar insolation
important for the southwest monsoon, climate, agriculture and harnessing solar
energy.
Bridging Science and
Society
· Anna Mani,
India's atmospheric scientist, mapped solar insolation across India in the
1950s. She later published Solar Radiation Over India (1981) creating
the country's first insolation atlas.
· Her
pioneering measurements showed India’s vast solar energy potential. Today,
large-scale solar power deployment is helping build a resilient, sustainable,
and solar-powered energy future.
Example: How much
solar energy will be received by a 1 m² area in one hour, if the insolation on
the surface of the Earth were 1 kW m⁻²?
Answer:
E = Intensity × area ×
time
E = 1 × 1000 J s⁻¹ m⁻² ×
1 m² × 3600 s
E = 3600000 J = 3.6 ×
10⁶ J
(This energy is enough
to melt 5 kg of ice and heat the resulting water to 100 °C. It is also equal to
one unit of household electricity).
Think as a Scientist
·
Even a fraction of the Thar Desert, if covered
with solar panels, could supply the country’s electricity demand.
Interaction of solar radiation on
the Earth's surface
- Dark surfaces absorb more sunlight and heat up quickly. E.g., dark
coloured roads and clothes.
- Light coloured surfaces reflect more sunlight and remain cooler.
So, dark coloured clothes feel hotter than white ones in summer.
- The fraction of solar radiation reflected by a surface is called
its albedo (=whiteness in Latin).
- High albedo surfaces stay cool because they reflect more light. Low
albedo surfaces heat up more quickly as they reflect less and absorb more
light.
Reflection of solar radiation by surfaces of materials
|
S.
No. |
Materials |
Albedo |
|
1. |
Snow |
0.80 - 0.90 |
|
2. |
Ice |
0.50 - 0.70 |
|
3. |
Crushed rock |
0.25 - 0.30 |
|
4. |
Light
coloured soil |
0.25 – 0.45 |
|
5. |
Black soil |
0.05 – 0.15 |
|
6. |
Ocean water |
0.05 – 0.10 |
- Snow and ice have high albedo and reflect much of the incoming
solar radiation. That’s why polar regions are very cold. Black soil and ocean
water have low albedo, absorb more solar radiation, and remain warmer.
- All objects radiate heat. Concrete houses re-radiate stored heat
at night, making them hot in summer. Traditional mud and wooden houses stay
cooler due to less re-radiation.
Solar radiation and warming of the Earth
Threads of Curiosity
· Cities are
warmer than nearby rural areas, especially during summer and at night. Buildings
and roads made of steel, concrete, brick and asphalt absorb solar radiation and
retain heat. The re-radiation of this heat warms cities. This increases energy
demand for air conditioning. This is called Urban Heat Island Effect.
· Rural areas
and forests stay cooler because vegetation provides shade and transpiration.
Latitude and Earth's shape
- Because Earth is spherical, the Sun’s rays strike different
latitudes at different angles.
- The Sun’s radiation is concentrated over a smaller area near the
equator but spread over a larger area near the poles. Hence, equatorial regions
remain warm, while polar regions stay colder. This uneven heating creates
temperature differences between equator and poles.
- Earth's spherical shape and tilted axis cause seasons and
changing day length during its revolution around the Sun. Thus, solar radiation
and heating is unevenly distributed across the globe, driving global winds and
ocean currents.
Role of the atmosphere
- The atmosphere is the layer of air surrounding Earth. It
is held in place by gravity.
- It consists of nitrogen (78%), oxygen (21%), small amounts of
argon, CO2, water vapour, etc.
- The atmosphere has a layered structure that helps explain key
weather patterns.
Layers of the Earth’s atmosphere
- Troposphere (average height 12 km): Here, nearly, all
weather phenomena occur. It is heated from the Earth's surface. Temperature
decreases with height (~6.5°C/km). As the warm air rises, it drives winds and
storms. The troposphere is highest above the equator and lowest above the poles.
- Stratosphere (12–50 km): Here, the ozone layer
absorbs UV rays, causing temperature to rise with height. This reduces vertical
air mixing, keeping the layer stable and weather confined to the troposphere.
- Above the stratosphere are the mesosphere, thermosphere
and exosphere. They play only a minor role in regulating climate.
- Outer space begins at about 100 km above Earth.
Key atmospheric layers
|
Layer |
Altitudes |
Features |
|
Troposphere |
0-12 km |
Weather
formation; temperature decreases with height |
|
Stratosphere |
12-50 km |
Ozone layer
absorbs UV; temperature increases with height |
Meet a Scientist
· K. R. Ramanathan, India's atmospheric scientist, climbed to 18,000 feet in
the Himalayas in 1934 to measure ozone levels and found them lower than
expected.
·
His work helped explain how UV absorption varies with
altitude and pollution.
·
He later led early monsoon forecasting efforts.
- The atmosphere plays two crucial roles in protecting life on
Earth.
o It partly absorbs incoming solar radiation. The ozone layer
blocks the harmful UV rays. Clouds and gases absorb some sunlight before it
reaches Earth surface.
o It traps outgoing heat. The Earth absorbs sunlight and
re-radiates it as infrared (heat). Greenhouse gases absorb this heat,
preventing it from escaping into space. Without the atmosphere, the Earth would
be too cold for life to survive.
- Excess CO₂ from human activities enhances the greenhouse
effect, causing global warming. It makes the Earth uninhabitable.
- Although Mercury is closer to the Sun, Venus is hotter due to
its atmosphere and extreme greenhouse effect.
- Natural processes constantly change the atmosphere, affecting
weather, climate, and energy. Interaction of atmosphere with solar radiation
and cosmic rays also influences communication systems. Thus, atmosphere makes
the Earth a unique planet.
Threads of Curiosity
·
Ozone layer protects life by absorbing UV radiation.
·
In the late 20th century, chlorofluorocarbons
(CFCs) from refrigerators and aerosols caused severe ozone loss over
Antarctica, known as the ozone hole.
·
The Montreal Protocol reduced CFC use, and the
ozone layer is now slowly recovering.
UNEVEN HEATING CAUSES WIND AND OCEAN CURRENTS
- Wind is the movement of air from high-pressure region to
low-pressure region.
- The pressure difference is due to the uneven heating of the
Earth's surface by the Sun.
- Uneven heating of land and water also creates land and sea
breezes.
Local winds
- Uneven heating of the Earth's surface also produces local winds,
such as valley and mountain breezes.
- In mountainous regions, the slopes and the valley floor do not
heat up and cool down at the same rate.
- During the day, mountain slopes heat up faster than the valley
floor. The warm air above the slopes rises, creating a low-pressure area.
Cooler, high-pressure air from the valley then moves up the slope to replace it.
This is called a valley breeze.
- After sunset, mountain slopes cool down faster, while the valley
floor remains relatively warmer. This cooler, denser air over the slopes flows
down into the valley. This is called a mountain breeze.
- Such daily local wind changes happen in hilly regions like
Shimla, Dehradun, and other Himalayan valleys.
- These regulate temperature and moisture, supporting agriculture
and daily life.
- Thus, uneven heating of Earth forms an important part of the
Earth's atmospheric circulation.
Planetary winds
- Uneven heating between the equator and poles creates high and
low-pressure belts. This massive pressure difference moves air over long
distances, forming planetary winds.
- Near the equator, intense heat causes warm air to rise, forming
an equatorial low-pressure belt. This air moves towards the poles, cools
down, becomes denser and sinks around 30° N and S latitudes, creating sub-tropical
high-pressure belts. Air then flows along the surface from these
high-pressure areas back to the equator, completing the cycle.
- Not all sinking air returns to the equator. A part of it moves
towards the poles and rises again around 60° N and S latitudes where it meets
the cold air from the polar regions. It creates sub-polar low-pressure belts.
- Meanwhile, extreme cold at the poles (90° N and S) causes dense
air to sink, forming polar high-pressure belts. Air then flows from
these poles toward the sub-polar belts, completing another circulation cycle.
Wind
circulation between equatorial low-pressure belt and sub-tropical high-pressure
belt
- Earth's rotation deflects planetary winds from straight paths
into curved paths. As they move from high to low pressure, winds deflect to the
right in the Northern Hemisphere and to the left in Southern
Hemisphere.
The distribution of pressure belts and planetary winds
Ocean currents
- Ocean currents are the continuous movement of large
masses of ocean water. These are also driven by planetary winds and pressure
differences.
- Strong planetary winds drag ocean surface water through
friction, setting surface currents in motion.
- Besides winds, water temperature, salinity, Earth's rotation and landmass shapes influence
ocean currents.
o Temperature is varied in equatorial & polar waters.
Warm equatorial waters flow along the surface toward the poles, while colder,
denser waters slowly flow back to the equator through deep ocean levels.
o Ocean salinity also varies by location. Less dense, low-salinity water stays near the surface,
while denser, high-salinity water sinks and moves through deeper levels.
o Earth's rotation deflects moving water masses, forming
large circular currents called gyres. These rotate clockwise in
the Northern Hemisphere and counter-clockwise in the Southern
Hemisphere.
o Continents further modify these paths by blocking and
redirecting the currents.
Global surface ocean
currents showing circulation like gyres
- Ocean currents regulate climate and support life and massive
ecosystem by transporting nutrients.
- They reduce global temperature differences by transporting heat
from the equator to the poles. E.g., the warm North Atlantic Drift, an
extension of the Gulf Stream (an ocean current from the southern part of the
North American east coast across the Atlantic Ocean) flows to the northwestern
Europe keeping ports ice-free during winter even at high latitudes. This moderating
climate supports human activities like trade and commerce.
Gulf
Stream brings warm water from the equator
Pause and Ponder
· How does the cool mountain breeze benefit agriculture
activity, particularly the crops
and soil?
Answer: It maintains moderate
temperatures, reduce excessive evaporation, and preserve soil moisture. This
creates favourable conditions for crop growth and improves agricultural
productivity.
· What happens
to the warm surface of water from the equator as it travels toward the poles?
What impact does this movement have on the area?
Answer: Warm surface water gradually
cools. It transfers heat to the surrounding atmosphere, making nearby coastal
regions warmer and helping to moderate the climate.
India's Scientific
Contributions
· Scientists at
Indian Institute of Tropical Meteorology (IITM), Pune use advanced computer
models to simulate the Indian monsoon by connecting energy flows between the
atmosphere, oceans, land, and ice.
· By using data
from satellites, ocean buoys, and Antarctica, these models improve seasonal
forecasts and help study how global warming affects monsoon rainfall across
India.
BIOGEOCHEMICAL CYCLES
- The cyclic movement of matter and energy between abiotic (non-living)
and biotic (living organisms) components is called biogeochemical
cycle.
- This exchange results in transfer of matter and energy across
Earth's spheres. It also recycles nutrients like carbon, nitrogen, and oxygen.
- This dynamic relationship between ecosystems helps recover from disturbances and maintains
environmental balance.
Water cycle
Water cycle
- It includes evaporation, transpiration, condensation,
precipitation, infiltration and groundwater.
- Water evaporates from water bodies (rivers, lakes, oceans, etc.)
and condenses to form clouds. It returns to the surface as precipitation
(rain, hail or snow) and finally flows back to the ocean. Some water seeps
through soil and rocks.
- Water dissolves minerals from soil and rocks. It also supports
all terrestrial organisms and transports these nutrients to oceans, and support
marine life.
- Climate change affects the water cycle. E.g.,
o Warmer atmosphere holds more moisture, causing heavy rains (like
intensified monsoons) in some areas and droughts elsewhere.
o Melting glaciers add water to rivers, raising sea levels and threatening coastal cities like Mumbai &
Chennai.
o Sudden intense rainfall causes soil-erosion and less
infiltration, reducing groundwater
recharge. It makes agriculture difficult during dry months.
-
Thus, water cycle links the
cryosphere (glaciers), hydrosphere (rivers & oceans), atmosphere
(moisture), geosphere (soil erosion & decreased infiltration), and biosphere (crops & fisheries), all affected by global warming.
Carbon cycle
- Carbon circulates between
atmosphere (CO₂), biosphere (plants & animals), geosphere (carbonate
rocks and fossil fuels- coal & oil), and hydrosphere (dissolved CO₂ and
marine shells).
Carbon
cycle
-
Different parts of the
carbon cycle operate at different time scales.
o Fast cycle (days to years): Plants convert CO₂ into
glucose via photosynthesis. Respiration releases CO₂ back into the
atmosphere. Animals consume other organisms. When they die, decomposition
returns CO₂ to the air.
o Slow cycle (millions of years): Buried organic matter
converts into fossil fuels (coal, oil & gas). Burning these fuels releases
carbon back as CO₂ rapidly.
-
The atmosphere and ocean
continuously exchange CO₂. Ocean water absorbs atmospheric CO₂ to form
carbonate & bicarbonate ions. Phytoplankton use them for photosynthesis.
Some marine organisms also use them to form shells. Upon death, organisms sink
to the ocean floor and their organic matter
is stored as carbon.
- Burning fossil fuels and deforestation raised CO₂ by about 35%
since 1960 (315 to 420 ppm (parts per million). While some CO₂ is necessary to
keep the Earth warm enough to sustain life, the balance is critical.
Atmospheric CO₂ concentration (1960 – 2025), the Keeling curve.
The sawtooth pattern shows seasonal dips from yearly plant growth in the
Northern Hemisphere absorbing CO₂
- Excess CO₂ causes greenhouse effect leading to global
warming, melting glaciers and Arctic sea ice, rising sea level and extreme
weather. In India, this leads to intense monsoons and threatens agriculture.
- Though fossil fuels still dominate electricity generation, India
is rapidly increasing renewable energy like solar energy to minimize carbon
emissions.
Pause and Ponder
· The CO₂
dissolved in the ocean is disturbed when the global temperature increases. What
will happen to marine life?
Answer: The amount of CO₂ in the ocean is
disturbed, leading to ocean warming and acidification. It harms organisms (corals,
shellfish, plankton etc.), disrupts marine food chains, and reduce marine
biodiversity.
Threads of Curiosity
· Carbon makes
up ~49% of the dry weight of living organisms. Oceans hold 71% of global
carbon, acting as a major reservoir that regulates atmospheric CO2.
The atmosphere holds only about 1% of total global carbon.
Nitrogen cycle
- Nitrogen is an essential for the synthesis of proteins and
nucleic acids in living organisms.
- The largest reservoir of nitrogen is in atmosphere.
- Nitrogen (N₂) is non-reactive and cannot be directly used by
plants and animals. It must first be converted into soluble compounds that
organisms can absorb.
- The overall movement of nitrogen among air, soil, water, and
organisms is called the nitrogen cycle.
Nitrogen cycle
Steps of nitrogen cycle:
o Nitrogen fixation: In this, Nitrogen-fixing bacteria
like Rhizobium (in legume root nodules) and Azotobacter (in soil)
convert atmospheric N₂ into ammonia (NH₃).
Lightning
also fixes atmospheric nitrogen.
o Nitrification: In this, nitrifying bacteria like Nitrosomonas
convert ammonia into nitrite (NO₂⁻) and Nitrobacter convert nitrite into
nitrate (NO₃⁻).
o Assimilation: Plants assimilate these nitrogen compounds
from the soil. Animals obtain nitrogen by consuming plants or other animals.
o Ammonification: When plants and animals die or produce
waste, decomposers (bacteria & fungi) break the organic matter,
returning ammonia to the soil.
o Denitrification: In this, denitrifying bacteria like
Pseudomonas convert some nitrates back into N₂ gas. This completes the
cycle and maintains a balance of nitrogen in ecosystems.
Ready to Go Beyond
· Lightning
fixes some atmospheric N₂ into nitrogen oxides. Today, most N₂ is fixed
artificially via energy-intensive Haber-Bosch process (1-2% of global
energy) to make ammonia for fertilizers. This 'Bread from Air' enabled India's Green
Revolution. Today, over half the nitrogen atoms in our bodies come from
this process. However, fertilizer overuse degrades soil and water.
Oxygen cycle
- Oxygen is one of Earth's most abundant elements.
- 21% of the atmosphere consists of free oxygen (O₂).
- Oxygen also exists combined in Earth's crust as metal
oxides/minerals and in air as CO₂.
- Organisms use O₂ for respiration and releases CO₂. Combustion
of fuels uses O₂ and releases CO₂.
- Plants restore O₂ via photosynthesis using sunlight, water and
CO₂ to form glucose and release O₂. This balance between consumption
(respiration and combustion) and production (photosynthesis) circulates O₂ across
Earth's spheres, sustaining life.
Oxygen
cycle
Pause and Ponder
· What would
happen to plants and animals on Earth if the biogeochemical cycles were
disrupted and stopped? Explain by giving a few examples.
Answer: If biogeochemical cycles were
disrupted and stopped, essential nutrients would no longer be recycled in
nature. Plants would not get enough nutrients such as carbon, nitrogen, and
phosphorus for growth, leading to reduced plant populations. Animals would be
affected because they depend on plants directly or indirectly for food. E.g.,
o Carbon cycle
stops →
photosynthesis decreases.
o
Nitrogen cycle stops → plants cannot make proteins.
o Water cycle
stops → Disturb
ecosystems.
HUMAN IMPACT ON EARTH'S PROCESSES
- Excess atmospheric CO₂ increases ocean absorption, making
seawater more acidic. This threatens plankton and coral reefs, disrupting
marine ecosystems. However, warmer water reduces the ocean's CO₂ absorption
capacity as a carbon sink.
- Fossil fuel burning and deforestation saturate natural carbon
sinks like forests and oceans.
- In India, fossil fuels still dominate electricity generation,
causing harmful emissions. Excess CO₂ intensifies greenhouse warming,
disrupting carbon cycle.
- Overuse of fertilizers adds excess nitrates to water bodies,
causing widespread growth of algae (algal blooms) that deplete oxygen
and kill fish. This is called eutrophication. It threatens water bodies and
coastal fisheries.
- Deforestation creates multiple effects across air, water,
land and organisms. E.g.,
Clearing forests
decreases photosynthesis and transpiration which decline local rainfall. It
also alters surface albedo. Without tree roots, soil erosion increases. Over
time, habitat destruction causes biodiversity decline as species lose their
homes.
·
If photosynthesis is stopped, what would happen on
the Earth?
Answer:
If photosynthesis stopped plants would no longer produce food or release
oxygen. CO₂ levels would increase while oxygen levels would decrease. Plants
would die first followed by herbivores and then carnivores due to the lack of
food. Eventually the ecosystems would collapse.
- Vehicular emissions react with sunlight to form ground-level
smog. This forms ground-level ozone, which harms health, unlike
stratospheric ozone. These pollutants make city air unhealthy.
Restoring Environmental Balance
· Local actions and global cooperation can restore natural
systems. E.g., Montreal Protocol initiated ozone layer recovery through
global cooperation. However, Kyoto Protocol and Paris Agreement,
aimed at reducing CO₂ emissions, have been less successful.
· Conserving energy, switching to renewable energy resources
(solar/wind), planting trees, saving water, and sustainable farming.
India has planted
billions of trees, expanded solar and renewable energy, and promoted
sustainable farming.
· Individuals can contribute by saving water, food, and energy
resources. It involves reducing waste, reusing, and recycling materials.
Threads of Curiosity
·
Introduced in 2021, Mission LiFE (Lifestyle
for Environment) is an India-led global initiative promoting eco-friendly
living. It views Earth as an interconnected system driven by energy flow and
matter cycling. Mission LiFE focuses on simple, individual habits like saving energy and resources to build a sustainable
future.
Pause and Ponder
· Discuss how
human activities increase the concentration of greenhouse gases in the
atmosphere. What would you do as an individual to reduce the emission of
greenhouse gas?
Answer: Human activities such as burning
fossil fuels, deforestation, industrial processes, and intensive agriculture
increase the concentration of greenhouse gases. These contribute to global
warming.
I
can help reduce greenhouse gas emissions by:
o Using public
transport, cycling, or walking.
o Conserve
electricity.
o Planting and
protecting trees.
o Reducing,
reusing, and recycling waste.
o
Avoiding unnecessary use of fossil fuels.