Earth Science

Question 0

Explain Earth’s structure

Answer 0

1. The outermost layer of the Earth is the crust, which consists of the continents and the ocean floors.

Continental crust is typically about 22–43 miles (35–70 km) thick, while oceanic crust is thinner, typically only about 3–6 miles (5–10 km) thick.

The silicate rocks granite and basalt are the most common rocks in the Earth’s crust.

2. The next layer is the mantle, composed mainly of hot, mushy silicates.

It is about 1,800 miles (2,900 km) thick. Large convective cells in the mantle circulate heat and drive plate tectonics.

3. The Earth has a fluid, iron-rich outer core and a solid inner core, which is probably mostly made of iron with some nickel.

The temperature inside the Earth is thought to rise by about 45–54°F (25–30°C) for each kilometer of depth. Some of that heat is left over from the planet’s formation, but most comes from the radioactive decay of unstable elements.

Scientists deduce the Earth’s deep internal structure by measuring how seismic waves from earthquakes propagate through it.

Question 1

Give brief account of earth history

Answer 1

1. The Earth formed around 4.56 billion years ago, when matter gradually clumped together in a swirling disk of gas and dust around the Sun.
2. The young Earth was hot enough for heavy metals inside to melt and sink into the planet’s core, creating a separate core and mantle.
3. About 4.53 billion years ago, a Mars-size body is thought to have crashed into the Earth, creating the Moon.
4. The Earth’s history is divided into four eons, starting with the
5. a) Hadean, which lasted until 3.8 billion years ago. Toward the end of the Hadean, Earth was pummeled by meteorites during the “late heavy bombardment.” Water-bearing comets also pelted the Earth’s surface, delivering water to form oceans.

Life arose on Earth soon after the late heavy bombardment, and photosynthesis by primitive plants began enriching the atmosphere with oxygen around 3 billion years ago.

4.b) During the current Phanerozoic eon, covering the last 542 million years, the continents gradually merged into a single landmass called Pangaea, then later split to form the familiar continents today.

Question 2

Explain Geomagnatism

Answer 2

1. Geomagnetism refers to the Earth’s magnetic field, which is similar to that of a bar magnet.
2. a) The magnetic north and south poles are close to the geographic poles, but the magnetic poles wander by up to about 25 miles (40 km) each year.
3. The northern and southern lights (“aurorae”) are eerie glows that occur near the magnetic poles when energetic particles from the Sun excite atmospheric molecules.
4. The dynamo theory suggests that Earth’s magnetic field sustains itself via a feedback mechanism.

The field induces electric currents in the metallic liquid outer core, while convection currents and the Earth’s rotation organize these currents into spirals aligned from north to south.

These currents induce a magnetic field that reinforces the original field, creating a self-sustaining dynamo.

4. Magnetic fields preserved in ancient lava flows show that the Earth’s magnetic field flips over every few hundred thousand years or so, with the north pole moving to the south pole, and vice versa. There is no consensus on why this happens.

Question 3

Explain Earth’s shape

Answer 3

1.The Earth’s shape is a flattened sphere because it bulges out at the equator slightly due to its rotation.

Its average diameter is 7,918 miles (12,742 km), but the polar diameter is about 0.3 percent less than the equatorial diameter.

2. The coordinate system for Earth’s surface uses lines of latitude and longitude. Longitude lines run north to south, while latitude lines form circles that get smaller toward the poles.

By convention, the “prime meridian” that passes through Greenwich in London marks zero longitude, while zero latitude falls on the equator.

The positions of any point on Earth’s surface can then be described in degrees north or south and east or west. New York, for instance, is at 41° North, 73° West.

3. Surveyors and engineers often use the concept of the geoid, a hypothetical Earth surface that represents the mean sea level. It is useful because it represents the horizontal everywhere, and gravity acts perpendicular to it. Water will not flow in an aqueduct, for instance, if its pipes are perfectly aligned along the geoid.

Question 4

Explain Seasons

Answer 4

1. Earth’s orbit is almost circular, with its distance from the Sun varying by only about 3 percent over the course of a year. This means that the solar energy received on Earth changes by about 6 percent. However, this is not the cause of the seasons—hot summers and cold winters are due to the 23.5° tilt of the Earth’s rotation axis.
2. The tilt makes more sunlight fall on the northern hemisphere than the southern hemisphere during the northern summer, the peak occurring on the summer solstice on June 20/21.

More solar energy falls on the southern hemisphere in December, peaking at the solstice on December 21/22.

Sunlight is equal in both hemispheres at the vernal or spring equinox (March 20/21) and the autumnal equinox (September 22/23).

3. Earth’s large axial tilt also means that any regions inside the Arctic and Antarctic circles, at latitudes of more than 66° North or South, will experience a period of permanent sunlight in summer and permanent darkness in winter.

Question 5

Explain plate tectonics

Answer 5

1. Plate tectonics describes the movement of the Earth’s lithosphere, consisting of its rigid crust and upper mantle.
2. This is the driving force behind continental drift, which saw a single vast supercontinent called Pangaea break up roughly 250 million years ago, fragmenting to form the familiar modern continents such as Africa and Europe.
3. The lithosphere divides into several major tectonic plates that move on the mobile mantle underneath. Dense old lithosphere sinks into the deep mantle at “subduction zones,” while new crust is formed by volcanic eruptions at midocean ridges.
4. The speed of tectonic plates is typically very slow—roughly as fast as your fingernails grow.

Where tectonic plates collide, mountain ranges can form, while divergent faults occur when plates move apart. “Transform boundaries” form where plates are sliding past each other.

5. Earthquakes and volcanoes usually coincide with plate boundaries, although volcanism can also occur at “hotspots” within plate interiors, which overlie hot mantle plumes.

Question 6

Explain faults

Answer 6

1. fault is a fracture or discontinuity in rocky terrain where two masses of rock have moved relative to each other.

Some faults are tiny, but others are part of vast fault systems criss-crossing the Earth at the boundaries of major tectonic plates.

2. The sudden movement of faults causes earthquakes.

Faults that have horizontal movement are called strike-slip faults,

while those with primarily vertical movement are called dip-slip faults.

A divergent fault is one where two plates gradually move apart, sometimes creating midocean ridges as underlying magma wells up through cracks in the oceanic crust and cools.

Tectonic plates collide at convergent faults. Sometimes, this makes oceanic crust slide beneath the other plate, forming a subduction zone.

The collision of two continental plates can drive up huge mountain ranges like the Himalayas.

A transform fault is one where tectonic plates slide past each other horizontally. A classic example is the San Andreas Fault in California, which has triggered several major quakes.

Question 7

Explain Earthquake

Answer 7

1. Earthquakes occur when a sudden release of energy in the Earth’s crust shakes the ground by generating seismic waves.
2. They happen because tectonic plates don’t glide over each other smoothly without friction. Instead, their roughness makes them lock together, allowing stresses and strains to build up until they lurch sharply.
3. Divergent faults pulling apart trigger “normal” earthquakes, convergent plates cause “thrust” earthquakes, and transform faults, where plates slide past each other, cause “strike-slip” quakes.
4. Traditionally, the power of earthquakes has been measured on the Richter scale, and quakes with magnitudes above nine devastate areas thousands of miles across.
5. When an earthquake occurs under the sea, the seabed sometimes moves enough to trigger tsunamis, giant waves that can devastate coastal regions.
6. An earthquake in December 2004 off the coast of Sumatra, Indonesia, caused the worst tsunamis in recorded history, killing more than 2,30,000 people in fourteen countries.

Question 8

Explain Volcanos

Answer 8

1. Volcanoes form when hot molten rock, or magma, wells up through the Earth’s crust due to heating from the mantle beneath.
2. They’re often found along boundaries where tectonic plates converge or diverge—for instance, along the Mid-Atlantic Ridge where plates are pulling apart.
3. Volcanoes also occur at “hotspots” far from plate boundaries, where the crust overlies a hot mantle plume.
4. Eruptions at an undersea hotspot formed all of the Hawaiian islands, for instance.
5. Volcanoes often form conical mountains that spew lava, ash, and gases from a collapsed crater, or caldera, at the top, but others have rugged peaks formed by lava domes.
6. Pyroclastic flows of searing hot gas, ash, and rock often speed away from an erupting vent at up to 90 mph (150 km/h), hugging the ground.
7. Volcanoes also eject volcanic “bombs,” blobs of molten rock up to several miles wide, which cool and crust over before hitting the ground.
8. The most deadly eruption in recorded history was that of Indonesia’s Mount Tambora in 1815, which killed at least seventy-one thousand people.

Question 9

Explain rock types

Answer 9

1. geologists classify rocks into three main groups: igneous,
   sedimentary, and
   metamorphic.

1.a) Igneous rocks form when hot molten rock, or magma, rises through the Earth’s crust, then cools and solidifies.

When magma slowly cools deep underground, large crystals grow inside it, creating coarse-grained rock such as granite, while rapid cooling at the surface creates fine-grained rock such as basalt.

1.b) Sedimentary rocks form on the Earth’s surface. They are layered accumulations of sediments, including rock fragments, minerals, and animal and plant material.

One example is sandstone, which forms when sand settles out of water, then becomes compacted by overlying deposits.

Sedimentary rocks probably make up only about 5 percent of the Earth’s crust, forming a thin veneer over igneous and metamorphic rocks.

1.c) Metamorphic rocks were once sedimentary or igneous rocks, but their densities increased and their compositions changed when they were pulled deep down into the Earth’s crust and subjected to high pressures and temperatures.

Question 10

Explain the rock cycle

Answer 10

1. The rock cycle describes the endless natural recycling processes that rocks undergo on the restless Earth, continually changing over millions of years due to processes such as erosion and tectonic plate motions.

The rock cycle is particularly active where tectonic plates meet.

2. The cycle begins with magma, fluid or mushy hot rock beneath the Earth’s surface, which cools and crystallizes to form igneous rocks.
3. These rocks can return to their roots as magma by “subduction,” being dragged back down through the crust to melt again.
4. Alternatively, burial of igneous rocks can compress and heat them to form metamorphic rock.
5. At the Earth’s surface, rocks are weathered and eroded into fragments and grains. Rivers and streams sweep these particles away and deposit them in lakes and seas, beginning the process of sedimentation that creates sedimentary rock.
6. Continental crust recycles very slowly, and Earth’s current continental crust is typically about 2 billion years old, while the oldest oceanic crust is only about 200 million years old.

Question 11

Explain fossils

Answer 11

1. Fossils are the remains of animals, plants, and other living organisms that have been preserved for thousands of years inside sediments, which have gradually replaced their tissues with minerals.
2. Fossilization can preserve the remains of animals or plants that are buried soon after they die. For instance, the soft parts of a dead fish might rot away while its skeleton becomes buried in muddy or sandy sediments, retaining its structure as the sediments are compacted into stone.
3. Minerals gradually replace the skeleton by filling voids left as the skeleton slowly dissolves. Millions of years later, this skeleton “copy” can become exposed through mountain or cliff uplift and erosion.
4. Like living organisms, fossils can range from microscopic single cells to gigantic dinosaurs and trees.
5. Fossils may also preserve the marks left by animals in sediments, such as footprints of our early human ancestors.
6. The oldest known fossils are stromatolites, fossilized colonies of microbes that date back for 3.4 billion years or more.

Question 12

Explain topography

Answer 12

1. In geography, topography is the study and mapping of Earth’s surface shape and features in three dimensions.
2. Topographic maps, or relief maps, record the height of terrain using contour lines, with each contour line tracking land of equal height. So mountains appear as concentric loops, the steepest slopes indicated by the most tightly packed contours.
3. Detailed information about terrain and surface features is essential for planning and executing any major projects in civil engineering or land reclamation, for instance.
4. Photogrammetry is a traditional technique for locating 3D coordinates of points on the ground by comparing two or more aerial photos taken from different angles.
5. Digital data for precise relief maps of the Earth’s surface come from satellite radar mapping of the land,

while sonar surveys from ships can measure the terrain on the ocean floors.

Airborne “lidar” (Light Detection and Ranging) systems can also map the detailed heights of forest canopies and glaciers, for instance, by measuring reflected visible laser light.

Question 13

Explain Continents

Answer 13

1. The continents are the seven biggest landmasses on Earth: Asia, Africa, North America, South America, Antarctica, Europe, and Australia.
2. They make up just over 29 percent of the Earth’s surface.
3. Oceans or seas separate most of the continents, except for Europe and Asia, which are often considered to be a single continent called Eurasia.
4. Close to 40 percent of the Earth’s total land surface is used for crops and livestock pasture, while roughly a quarter is mountainous.
5. Forests cover about a third of the land. In the tropics, most forests are lush tropical rainforest, with annual rainfall above about 6 ft (1.8 m).

Deserts are dry areas with less than 10 in (25 cm) of rainfall each year, making vegetation sparse or almost nonexistent.

Hot and cold deserts take up about one-fifth of the Earth’s land surface.

Temperate regions with relatively mild climates lie between the permanently hot tropics and the polar regions, while vegetation-poor tundra with permanently frozen subsoil dominates the ice-free land at high northern latitudes.

Question 14

Explain Oceans

Answer 14

1. The oceans are vast bodies of salt water that cover almost 71 percent of the Earth’s surface.
2. They are usually divided into five major oceans: the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Southern Ocean, and the Arctic Ocean.
3. Nearly half of all oceans, by area, are more than 9,800 ft (3 km) deep.

The deepest point overall is in the Mariana Trench in the Pacific south of Japan, which reaches down about 36,000 ft (11 km).

4. Two oceanographers, Don Walsh and Jacques Piccard, reached the bottom of the Mariana Trench in a small submersible in 1960—a feat no one else has achieved since.
5. Ocean currents act like giant conveyor belts to transfer heat from the tropics to the poles. Cold deep water rises and warms in the central Pacific and the Indian Ocean before heading to high latitudes where it sinks and cools.

An important ocean current system stretching from the southeast United States to northwest Europe incorporates the Gulf Stream and the North Atlantic Drift, and helps keep northwest Europe’s climate relatively warm.

Question 15

Explain surface water

Answer 15

1. About 97 percent of all water on Earth is in the salty oceans,

while only about 2.5 percent is fresh water. Most of that is tied up in the ice caps or lies underground.

In fact, only about 0.3 percent of Earth’s fresh water is in rivers and lakes, the sources of most water we use in everyday life.

2. When the Sun heats water in the oceans, it evaporates as water vapor that rises and condenses into clouds, before falling down as precipitation including rain and snow.
3. Water can be stored for thousands of years in the ice caps and glaciers, which contain about 70 percent of Earth’s fresh water.
4. Rainwater runs off land into rivers that flow to the oceans or into largely freshwater lakes.

There are many types of lakes, including “oxbow lakes” that form when the force of flowing water gradually exaggerates a meandering curve until it cuts off from the main river channel.

Lake Superior on the US–Canada border is often regarded as the largest freshwater lake by area, covering 31,820 square miles (82,400 square km).

Question 16

Explain Atmospheric chemistry and structure

Answer 16

1. The atmosphere is the shroud of gases around the Earth, held in place by gravity. It plays a vital role in making our planet hospitable to life, providing air to breathe and preventing large temperature swings between night and day.
2. The atmosphere is mainly composed of nitrogen (78 percent) and oxygen (21 percent), but its composition changes with height.
3. The lowest layer, the troposphere, is the densest and contains roughly 80 percent of the atmosphere’s mass.

The next layer is the stratosphere, and this contains the ozone (O3) layer, which absorbs most of the ultraviolet light from the Sun that would otherwise be harmful to life.

The outermost atmospheric layer is the thin exosphere, composed mainly of hydrogen and helium.

4. The Earth’s atmosphere looks blue because it scatters blue sunlight better than red sunlight, sending blue light photons in every direction.
5. Sunrises and sunsets appear red because the Sun is on the horizon, so its light passes on a long path through the atmosphere and more blue light is removed.

Question 17

Explain Atmospheric circulation

Answer 17

1. The atmospheric circulation is the large-scale movement of air that distributes heat across Earth’s surface.
2. It is dominated by Hadley cells, huge convection loops described by British lawyer and scientist George Hadley in the early 1700s.

Hadley cell circulation begins with moist, hot air at the equator rising and moving poleward, then descending at latitudes of about 30° North and South.

Some of the descending air travels across the surface back toward the equator, creating the trade winds that also veer toward the west due to the Earth’s rotation.

3. The polar cells are high-latitude convection loops at more than 60° North and South.
4. Ferrel cells, first proposed by nineteenth-century American meteorologist William Ferrel, are convection cells that operate at mid-latitudes but rotate in the opposite direction to polar cells and form westerlies due to the Earth’s rotation.
5. The jet streams—mainly the polar jets and subtropical jets—are high-altitude flows of fast-moving air that form at the boundaries between the cells and rotate toward the east.

Question 18

Explain weather fronts

Answer 18

1. In meteorology, weather fronts are boundaries separating masses of air with different density, temperature, and humidity.
2. Their approach signals the onset of a change in weather. For instance, when a cold front moves under a mass of warm moist air, the warm air rises and the moisture can condense into heavy rainclouds.
3. Cold fronts move faster than warm fronts and produce more sudden changes in weather because cold air is denser than warm air, and replaces it rapidly.
4. On weather maps, cold fronts are shown as lines of blue triangles pointing in the direction of travel.
5. Light rainfall often signals the approach of a warm front, depicted as a line with red semicircles.
6. An occluded front forms when a cold front overtakes a warm front.
7. A stationary front is effectively a stalemate between two fronts, neither strong enough to replace the other. It tends to hang around in the same place for a long time, often delivering rainy weather for several days.

Question 19

Explain clouds

Answer 19

1. A cloud is an opaque mass of water drops or ice crystals suspended in the atmosphere.
2. Clouds form because sunlight warms the Earth’s surface and evaporates water. Moist, warm surface air rises to higher altitudes where the water vapor condenses onto tiny particles like dust or salt, forming liquid droplets or ice crystals if it is cold enough.
3. Eventually, these become too large to be supported by upward air currents and fall as precipitation.
4. Cumulus clouds are puffy, dense clouds that sometimes look like cotton balls. They grow upward and can develop into giant cumulonimbus clouds that trigger thunderstorms.
5. Cirrus clouds are thin, wispy clouds blown by high winds into long streamers. They form at high altitudes above 20,000 ft (6 km), and usually accompany pleasant weather.
6. Clouds with the prefix “alto” are middle-level clouds, while stratus clouds are uniform grayish ones that often cover the entire sky.
7. All weather-related cloud types form in the troposphere, the lowest major layer of Earth’s atmosphere.

Question 20

Explain precipitation

Answer 20

1. Precipitation is any kind of water falling out of clouds, including rain, snow, sleet, and hail.
2. It happens when air turbulence inside clouds makes small water droplets or ice particles collide, producing larger ones. When they become too large to be supported by upward air currents, they fall to the ground.

(An exception is virga, light precipitation that evaporates before it hits the ground.)

3. Raindrops grow up to about 0.4 in (10 mm) across, the largest ones flattened into pancake shapes by oncoming airflow. Snowflakes can reach several centimeters wide.

Hailstones grow as they repeatedly rise and fall inside a cloud by moving in and out of an updraft, and can reach more than 8 in (20 cm) wide, big, and heavy enough to cause fatal injuries.

Question 21

Explain Haze, Mist, and Fog

Answer 21

1. Haze:
   - This is caused by smoke and dust particles in industrial areas or may be due to refraction of light in air of different densities in the lower atmosphere.
   - The term is usually used in connection with the REDUCTION OF VISIBILITY in regions of LOW HUMIDITY, less than 75%.
   - When visibility is less than 2km, haze is present.
2. Mist:
   - The condensation of water vapour in the air causes small droplets of water to float about forming clouds at ground level called mist
   - It reduces visibility to about 1km.
   - Unlike haze mist occurs in WET AIR, when relative humidity is over 75%.

Fog:

• Ordinary fog is due to WATER CONDENSATION ON DUST PARTICLES like smoke on house and factories.
• It only occurs in the LOWER STRATA of the atmosphere as a sort of dense GROUND CLOUD.
• The visibility in fog is even less than 1km.
• In industrial areas, like those of the Black Country and Northern England, very thick SMOKY FOG is formed, called SMOG. The visibility may be reduced to 200m.
• Fogs that occur on hills are called HILL FOGS. Very common in in morning, even in tropics, and disperse when the sun rises.
• In temperate land, when days are hot and nights are clear and still, fog may also result from cooling of land surface by radiation. The lower layers are chilled and water vapour in the atmosphere condenses to form RADIATION FOG or LAND FOG.
• When cooling surface is over the sea or when a damp air stream is brought into contact with a cold current as of Newfoundland, SEA FOG in formed. It varies in depth and thickness.

Generally speaking fogs are more common on sea than lands, and are most prevalent over coastal areas. The dry interiors experience haze or mist. Dense fogs are more likely to occur in the high and middle latitudes rather than the tropics.

Question 22

Explain Storms and Tornados

Answer 22

1. A storm is any disturbance in the atmosphere that causes severe weather. Storms arise when rising hot air creates a center of low pressure surrounded by high-pressure regions, leading to strong winds and the formation of storm clouds such as cumulonimbus clouds.
2. Thunderstorms occur in warm regions when humidity is high. Moist, warm air becomes unstable and rapidly rises, while cold air forms strong downdrafts beneath. Falling water drops and ice particles shear negative electric charge off rising ones, causing “charge separation” in the clouds that discharges in lightning strikes, heard as thunder claps.
3. Tropical cyclones occur at low latitudes when air rotates around a center of low pressure, fueled by heat released when moist air rises and condenses.

Major tropical cyclones are often called hurricanes or typhoons depending on location.

Tornadoes are violent, funnel-shaped wind storms that suck up debris and can persist for more than an hour. They are most common in the central United States, in an area dubbed Tornado Alley.

Question 23

Explain Lightning and Sprites

Answer 23

1. Lightning occurs during thunderstorms when electric charge separates inside clouds. As a thunderstorm brews, water droplets in rapidly rising warm air transfer electric charge to falling droplets and ice particles, making the base of a cloud negatively charged relative to the cloud tops. Lightning happens when the resulting electric field becomes powerful enough to discharge through the cloud or to the ground.

Cloud-to-ground lightning starts when a channel of charge, usually negative, zigzags downward in a forked pattern to the ground and connects with a “streamer” of positive charge reaching up. This creates a path for a lightning bolt that heats the air, triggering pressure waves that we hear as thunder.

2. The atmosphere also hosts high-altitude electrical discharges called sprites—usually red luminous glows that sometimes have bluish downward tendrils—and elves—red glows each lasting less than 0.001 seconds.

Many people have reported seeing hovering, glowing spheres of “ball lighting” at ground level, but the origin of this effect is a mystery.

Question 24

Explain Climate

Answer 24

1. The Earth’s climate describes regional average weather patterns, including factors such as typical temperature, humidity, wind, and rainfall at different times of the year.

A host of factors influence these patterns, including latitude, altitude, and the location of a landmass relative to an ocean.

2. The most commonly used climate classification system is the Köppen system, published by German climatologist Wladimir Köppen in 1884.

This assigns all regions to five main climate categories. These broad categories have twenty-eight subcategories in total.

Question 25

Explain the Koppen climate system

Answer 25

1. Air temperature and precipitation data have formed the basis for several climate classifications. One of the most important of these is the Köppen climate system, devised in 1918 by Dr. Vladimir Köppen of the University of Graz in Austria.
2. For several decades, this system, with various later revisions, was the most widely used climate classification among geographers. Köppen was both a climatologist and plant geographer, so that his main interest lay in finding climate boundaries that coincided approximately with boundaries between major vegetation types.
3. Under the Köppen system, each climate is defined according to assigned values of temperature and precipitation, computed in terms of annual or monthly values.
4. Any given station can be assigned to its particular climate group and subgroup solely on the basis of the records of temperature and precipitation at that place.
5. Note that mean annual temperature refers to the average of 12 monthly temperatures for the year. Mean annual precipitation refers to the average of the entire year’s precipitation as observed over many years.
6. The Köppen system features a shorthand code of letters designating major climate groups, subgroups within the major groups, and further subdivisions to distinguish particular seasonal characteristics of temperature and precipitation.

Question 26

Explain major climate group according to Koppen climate system

Answer 26

Five major climate groups are designated by capital letters as follows:

1. A Tropical rainy climates:

The average temperature of every month is above 18°C (64.4°F). These climates have no winter season. Annual rainfall is large and exceeds annual evaporation.

2. B Dry climates:

Evaporation exceeds precipitation on the average throughout the year. There is no water surplus; hence, no permanent streams originate in B climate zones.

3. C Mild, humid (mesothermal) climates:

The coldest month has an average temperature of under 18°C (64.4°F), but above –3°C (26.6°F); at least one month has an average temperature above 10°C (50°F). The C climates thus have both a summer and a winter.

4. D Snowy-forest (microthermal) climates:

The coldest month has an average temperature of under −3°C (26.6°F). The average temperature of the warmest month is above 10°C (50°F). (Forest is not gen- erally found where the warmest month is colder than 10°C (50°F).)

5. E Polar climates:

The average temperature of the warmest month is below 10°C (50°F). These climates have no true summer.

Note that four of these five groups (A, C, D, and E) are defined by temperature averages, whereas one (B) is defined by precipitation-to-evaporation ratios.

Groups A, C, and D have sufficient heat and precipitation for the growth of forest and woodland vegetation.

Question 27

Explain the sub groups of climate classification under Koppen system

Answer 27

Subgroups within the five major groups are designated by a second letter according to the following code:

1. S Semiarid (steppe) W Arid (desert):

(The capital letters S and W are applied only to the dry B climates.)

f Moist, adequate precipitation in all months, no dry season. This modifier is applied to A, C, and D groups.

w Dry season in the winter of the respective hemi- sphere (low-Sun season).

s Dry season in the summer of the respective hemi- sphere (high-Sun season).

m Rainforest climate, despite short, dry season in monsoon type of precipitation cycle. Applies only to A climates.

From combinations of the two letter groups, 12 distinct climates emerge:

A Tropical rainforest climate:
The rainfall of the driest month is 6 cm (2.4 in.) or more.

Am Monsoon variety of Af:
The rainfall of the driest month is less than 6 cm (2.4 in.). The dry season is strongly developed.

Aw Tropical savanna climate:
At least one month has rainfall less than 6 cm (2.4 in.). The dry season is strongly developed.

BS Steppe climate:
A semiarid climate characterized by grasslands, it occupies an intermediate position between the desert climate (BW) and the more humid climates of the A, C, and D groups.

BW Desert climate:
Desert has an arid climate with annual precipitation of usually less than 40 cm (15.7 in.).

C Mild humid climate with no dry season:
Precipitation of the driest month averages more than 3 cm (1.2 in.).

Cw Mild humid climate with a dry winter:
The wettest month of summer has at least 10 times the precipitation of the driest month of winter. (Alternative definition: 70 percent or more of the mean annual pre- cipitation falls in the warmer six months.)

Cs Mild humid climate with a dry summer:
Precipitation of the driest month of summer is less than 3 cm (1.2 in.). Precipitation is at least three times as much as the driest month of summer. (Alternative defi- nition: 70 percent or more of the mean annual precipi- tation falls in the six months of winter.)

Df Snowy-forest climate with a moist winter No dry season.

Dw Snowy-forest climate with a dry winter

ET Tundra climate
The mean temperature of the warmest month is above 0°C (32°F) but below 10°C (50°F).

EF Perpetual frost climate
In this ice sheet climate, the mean monthly tempera- tures of all months are below 0°C (32°F).

To denote further variations in climate, Köppen added a third letter to the code group. The meanings are as follows:

a With hot summer; warmest month is over 22°C (71.6°F); C and D climates.
b With warm summer; warmest month is below 22°C (71.6°F); C and D climates.

c With cool, short summer; less than four months are over 10°C (50°F); C and D climates.

d With very cold winter; coldest month is below –38°C (–36.4°F); D climates only.

h Dry-hot; mean annual temperature is over 18°C (64.4°F); B climates only.

k Dry-cold; mean annual temperature is under 18°C (64.4°F); B climates only.

As an example of a complete Köppen climate code, BWk refers to a cool desert climate, and Dfc refers to a cold, snowy-forest climate with a cool, short summer.

*** The boundaries for above types and formulas for its determination are given in Figure S7.4. (Introducing Physical Geography, Alan Strahler)

Question 28

Explain Global climate change

Answer 28

1. Many factors have altered the Earth’s climate over time, including tiny periodic variations in its orbit and the orientation of its spin axis.
2. Throughout much of Earth’s history, global average temperatures were more than 9°F (5°C) warmer than today and the poles were ice free. At other times, the world has been plunged into ice ages.
3. Climate change has also occurred in recent times. Between the mid-1500s and the mid-1800s, a period dubbed the “Little Ice Age,” average temperatures were roughly 1.8°F (1°C) cooler than today.
4. One possible reason is that atmospheric ash from volcanic eruptions cooled the planet by blocking sunlight.
5. Average temperatures increased by 1–1.6°F (0.6–0.9°C) during the twentieth century. Most scientists believe this is due to human activity, especially burning fossil fuels. This releases greenhouse gases, which trap some solar energy that would otherwise escape into space.
6. Temperatures could climb by several degrees during the twenty-first century, causing catastrophic sea-level rise and triggering frequent droughts and storms.

Question 29

Explain Ice ages

Answer 29

1. In ancient history, the Earth’s poles were sometimes ice free, but during ice ages, cool climates allowed vast ice sheets to grow over the continents.
2. There are many natural causes for this continuous climate change, including tiny changes in the tilt of Earth’s spin axis and movements of the continents.
3. Evidence for ice ages comes from geological features such as valleys carved by creeping glaciers as well as deep-drilled polar ice cores, which contain bubbles of ancient air that preserve temperature information.
4. The fossil record shows many organisms spread to warmer regions during cold periods.
5. There have been at least five major ice ages so far. The earliest well-established one occurred 2.5 to 2.1 billion years ago, while a cold period 850 to 630 million years ago may have seen “Snowball Earth” conditions with ice reaching the equator.
6. The current “Quaternary glaciation” began 2.58 million years ago. The Earth is now in an interglacial period, a relatively warm period within an ice age, while the last especially cold glacial period ended roughly ten thousand years ago.

Question 30

Explain Climate Engineering

Answer 30

1. Climate engineering describes proposed attempts to mitigate global warming on Earth caused by our use of fossil fuels. Each year, fossil fuel consumption releases billions of tons of carbon dioxide, a greenhouse gas.
2. Some climate engineering proposals would reduce the amount of greenhouse gases in the atmosphere directly—for instance,
   - by using industrial plants to mop up the gas, liquefy it, and then pump it underground or into the ocean floor.
   - Another idea is to add iron to the oceans, stimulating the growth of ocean phytoplankton that use iron as a nutrient and absorb carbon dioxide as they grow.
   - Another possible approach is to cool the Earth by cutting down the amount of solar energy reaching the atmosphere. Mirrors on spacecraft could reflect sunlight away, or aircraft could seed the atmosphere with aerosol particles that block out light.

These ideas are all in an early research phase—they remain largely unproven as solutions to global warming and could ultimately do more harm than good.

Question 31

What is Ramsar Convention on wetlands

Answer 31

1. The Ramsar Convention (formally, the Convention on Wetlands of International Importance, especially as Waterfowl Habitat) is an international treaty for the conservation and sustainable utilization of wetlands
   i. e., to stem the progressive encroachment on and loss of wetlands now and in the future, recognizing the fundamental ecological functions of wetlands and their economic, cultural, scientific, and recreational value.
2. It is named after the city of Ramsar in Iran, where the Convention was signed in 1971. There are 168 contracting parties.
3. India became part in 1982 and has 26 sites are deemed to be of “International Importance” under the Ramsar convention.

List of sites in India:

1 Ashtamudi Wetland, Kerala

2 Bhitarkanika Mangroves, Orissa

3 Bhoj Wetland, Madhya Pradesh

4 Chandra Taal, Himachal Pradesh

5 Chilika Lake, Orissa

6 Deepor Beel, Assam

7 East Calcutta Wetlands , West Bengal

8 Harike Wetland, Punjab

9 Hokersar Wetland, Jammu and Kashmir

10 Kanjli Wetland, Punjab

11 Keoladeo National Park, Rajasthan

12 Kolleru Lake Andhra Pradesh

13 Loktak Lake, Manipur

14 Nalsarovar Bird Sanctuary, Gujarat

15 Point Calimere Wildlife and Bird Sanctuary, Tamil Nadu

16 Pong Dam Lake Himachal Pradesh

17 Renuka Wetland Himachal Pradesh

18 Ropar, Punjab

19 Rudrasagar Lak, Tripura

20 Sambhar Lake, Rajasthan

21 Sasthamkotta Lake, Kerala

22 Surinsar-Mansar Lakes, Jammu and Kashmir

23 Tsomoriri, Jammu and Kashmir

[*120 Largest of the high altitude lakes in the Trans-Himalayan biogeographic region, the lake is oligotrophic with alkaline water.]

24 Upper Ganga River (Brijghat to Narora Stretch), Uttar Pradesh

25 Vembanad-Kol Wetland, Kerala

26 Wular Lake, Jammu and Kashmir

Question 32

Explain Bio-Geography

Answer 32

1. Biogeography focuses on the distribution of plants and animals—the biota—over the Earth.
2. It identifies and describes the processes that influence plant and animal distribution patterns.
3. Ecological biogeography looks at how the distribution patterns of organisms are affected by the environment.
4. Historical biogeography focuses on how spatial distribution patterns of organisms arise over time and space.

Question 33

Explain Food web

Answer 33

1. Energy is transferred through an ecosystem in steps, making up a food chain or a food web.
2. a) At the bottom of the chain are the PRIMARY PRODUCERS, which absorb sunlight and use the light energy to convert carbon dioxide and water into carbohydrates (long chains of sugar molecules) and eventually into other bio-chemical molecules, by PHOTOSYNTHESIS.
3. b) The primary producers support the CONSUMERS—organisms that ingest other organisms as their food source.

1.c) Finally, DECOMPOSERS feed on decaying organic matter, from all levels of the web.
Decomposers are largely microscopic organisms (microorganisms) and bacteria.

2. The food web is really an ENERGY FLOW SYSTEM, tracing the path of solar energy through the ecosystem.
3. a) Solar energy is absorbed by the primary producers and stored in the chemical products of photosynthesis.
4. b) As these organisms are eaten and digested by consumers, chemical energy is released. This chemical energy is used to power new biochemical reactions, which again produce stored chemical energy in the consumers’ bodies.
5. Energy is lost at each level in the food web through RESPIRATION. You can think of this lost energy as fuel burned to keep the organism operating.
6. In general, only 10 to 50 percent of the energy stored in organic matter at one level can be passed up the chain to the next level. Normally, there are about four levels of consumers.
7. The number of individuals of any species present in an ecosystem depends on the resources available to support them. If these resources provide a steady supply of energy, the population size will normally stay steady.

But resources can vary with time, for example, in an annual cycle. In those cases, the population size of a species depending on these resources may fluctuate in a corresponding cycle.

Question 34

Explain Photosynthesis and Respiration

Answer 34

1. Photosynthesis is the process in which plants combine water, carbon dioxide, and solar energy to form carbohydrate.
2. a) The rate of net photosynthesis depends on the intensity of light energy available, up to a limit.

Most green plants only need about 10 to 30 percent of full summer sunlight for maximum net photosynthesis.

Once the intensity of light is high enough for maximum net photosynthesis, the duration of daylight becomes an important factor in determining the rate at which the products of photosynthesis build up in plant tissues.

The rate of photosynthesis also increases as air temperature increases, up to a limit.

2. Respiration is the reverse process, in which carbohydrate is oxidized in living tissues to yield the energy that sustains life.
3. Day length, air and soil temperature, and water availability are the most important climatic factors that control net primary productivity.

Question 35

Explain Carbon Cycle

Answer 35

The carbon cycle is a BIOGEOCHEMICAL CYCLE in which CARBON FLOWS among STORAGE POOLS in the ATMOSPHERE, OCEAN, and on the LAND.

Human activity has affected the carbon cycle, causing carbon dioxide concentrations in the atmospheric storage pool to increase.

1. We’ve seen how energy from the Sun flows through ecosystems, passing from one part of the food chain to the next. Ultimately, that energy is radiated to space and lost from the biosphere.
2. Matter also moves through ecosystems, but because GRAVITY keeps surface material earth- bound, MATTER CAN’T BE LOST in the GLOBAL ECOSYSTEM.
3. As molecules are formed and re-formed by chemical and biochemical reactions within an ecosystem, the atoms that compose them are not changed or lost. In this way, matter is conserved, and atoms and molecules are used and reused, or cycled, within ecosystems.
4. Atoms and molecules move through ecosystems under the influence of both physical and biological processes.

We call the pathways that a particular type of matter takes through the Earth’s ecosystem a bio-geo-chemical cycle (sometimes referred to as a material cycle or nutrient cycle).

5. Any area or location of concentration of a material is a pool. There are two types of pools:

ACTIVE POOLS, where materials are in forms and places easily accessible to life processes, and

STORAGE POOLS, where materials are more or less inaccessible to life.

6. A system of pathways of material flows connects the various active and storage pools within the cycle. Path-ways can involve the movement of material in all three states of matter—gas, liquid, and solid.

For example, carbon moves freely in the atmosphere as carbon dioxide gas and freely in water as dissolved CO2 and as carbonate ion.

It also takes the form of a solid in deposits of limestone and dolomite (calcium and magnesium carbonate).

7. Ecologists have studied and documented biogeochemical cycles for many elements, including carbon, oxygen, nitrogen, sulfur, and phosphorus. Of these, the carbon cycle is probably the most important. That’s because all life is composed of carbon compounds of one form or another and human activities are modifying the carbon cycle in significant ways.

Question 36

Explain Nitrogen Cycle

Answer 36

1. The nitrogen cycle is another important biogeochemical cycle. NITROGEN MAKES 78% ATMOSPHERE by volume, so the atmosphere is a vast storage pool in this cycle.
2. Nitrogen as N2 in the atmosphere CAN’T BE ASSIMILATED DIRECTLY BY PLANTS OR ANIMALS. But certain MICROORGANISMS, including some soil bacteria and blue-green algae, can change N2 into useful forms in a process called NITROGEN FIXATION.

Legumes—such as clover, alfalfa, soybeans, peas, beans, and peanuts—are also able to fix nitrogen, with help from bacteria.

They have a symbiotic relationship with bacteria of the genus Rhizobium, which is associated with some 190 species of trees and shrubs.

The bacteria infect these plants’ root cells and supply nitrogen to the plant through nitrogen fixation, while the plants supply nutrients and organic compounds needed by the bacteria.

Crops of legumes are often planted in seasonal rotation with other food crops to ensure an adequate nitrogen supply in the soil.

3. Other soil bacteria convert nitrogen from usable forms back to N2, in a process called DENITRIFICATION that returns the nitrogen to the atmosphere.

Other processes are AMMONIFICATION, NITRIFICATION, and ASSIMILATION.

4. At the present time, nitrogen fixation far exceeds denitrification, thanks to human activity. We fix nitrogen in the manufacture of nitrogen fertilizers; by oxidizing nitrogen in the combustion of fossil fuels; and through the widespread cultivation of legumes.
5. At present rates, nitrogen fixation from human activity nearly equals all natural biological fixation, and usable nitrogen is accumulating in the Earth’s ecosystems.

Much of this NEWLY FIXED NITROGEN is carried from the soil into rivers and lakes and ultimately to the ocean, causing WATER POLLUTION.

The nitrogen stimulates the growth of algae and phytoplankton, which in turn REDUCE QUANTITIES OF DISSOLVED OXYGEN THROUGH RESPIRATION. Oxygen then drops to levels that are too low for many desirable forms of aquatic life.

These problems will be accentuated in years to come because INDUSTRIAL FIXATION of nitrogen in fertilizer manufacture is doubling about every six years at present.

The global impact of such large amounts of nitrogen reaching rivers, lakes, and oceans on the Earth’s global ecosystem remains uncertain.

Question 37

Explain Evolution, Natural Selection and Speciation

Answer 37

1. Sir Charles Darwin, whose monumental biological work, The Origin of Species by Means of Natural Selection, was published in 1859.
2. Through exhaustive studies, Darwin showed that all life possesses variation—the differences that arise between parent and offspring.
3. He proposed that the environment acts on variation in organisms in much the same way that a plant or an animal breeder does, picking out the individuals with qualities that are best suited to their environment. These individuals are more likely to live longer, propagate, and pass on their useful qualities.
4. Darwin termed this survival and reproduction of the fittest natural selection. He saw that, when acted upon by natural selection through time, variation could bring about the formation of new species whose individuals differed greatly from their ancestors.
5. Variation comes from two interacting sources: MUTATION and RECOMBINATION.

MUTATION :

A reproductive cell’s genetic material (DNA, or deoxyribonucleic acid) can mutate when the cell is exposed to heat, ionizing radiation, or certain types of chemical agents. Chemical bonds in the DNA are broken and reassembled.

Most mutations either have no effect or are harmful. But a small proportion of mutations have a positive effect on the individual’s genetic makeup. If that positive effect makes the individual organism more likely to survive and reproduce, then the altered gene is likely to survive as well and be passed on to offspring.

RECOMBINATION:

Recombination describes the process by which an offspring receives two slightly different copies, or ALLELES, of each gene from its parents.

One allele may be dominant and suppress the other, or the two alleles may act simultaneously. Because each individual receives two alleles of each gene, and there are typically tens of thousands of genes in an organism, the possible number of genetic combinations is very
large. Thus, recombination provides a constant source of variation that acts to make every offspring slightly different from the next.

Speciation:

Mutations change the nature of species through time. But just what is a species? For our purposes, we can define a species (plural, species) as a collection of individuals capable of interbreeding to produce fer- tile offspring.

A genus (plural, genera) is a collection of closely related species that share a similar genetic evolutionary history.

Speciation is the process by which species are differentiated and maintained. Actually, speciation is not a single process. It arises from a number of component processes acting together through time.

We’ve already looked at two of these: mutation and natural selection.
A third speciation process is GENETIC DRIFT. Chance mutations that don’t have any particular benefit can still change the genetic composition of a breeding population until it diverges from other populations.

Genetic drift is a weak factor in large populations. But in small populations, such as a colony of a few pioneers in a new habitat, random mutations are more likely to be preserved.

Gene flow is the opposite process. Evolving populations exchange alleles as individuals move among populations, keeping the gene pool uniform.

Speciation often occurs when populations become isolated from one another, so there’s no gene flow between them. This geographic isolation can happen in several ways. For example, geologic forces may uplift a mountain range that separates a population into two dif- ferent subpopulations by a climatic barrier. Or a chance long-distance dispersal may establish a new population far from the main one. These are examples of allopatric speciation.

As genetic drift and natural selection proceed, the populations gradually diverge and eventually lose the ability to interbreed.