🃏 World physical geography (Geography)

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The Big Bang? — The most popular explanation of the universe’s origin, also called the expanding universe hypothesis; the big bang is generally dated to 13.7 billion years before the present. Edwin Hubble gave evidence in 1920 that the universe is expanding.

The nebular hypothesis? — Put forward by the German philosopher Immanuel Kant and revised by the mathematician Laplace in 1796: the planets formed from a cloud of material around a young, slowly rotating sun.

The crust? — The oceanic crust averages 5 km thick and the continental crust about 30 km — as much as 70 km in the Himalayan region.

The mantle? — Extends from the Moho discontinuity to a depth of 2,900 km. Its upper part, the asthenosphere (‘astheno’ means weak), reaches about 400 km and is the main source of magma.

The core? — Begins at 2,900 km. The outer core is liquid and the inner core solid; mostly nickel and iron, it is sometimes called the nife layer.

The shadow zone? — Earthquake waves are not recorded between 105° and 145° from the epicentre; beyond 105° no S-waves arrive, so the S-wave shadow zone is much larger than the P-wave one.

Continental drift? — Alfred Wegener, a German meteorologist, set out the continental drift theory in 1912. Around 200 million years ago the supercontinent Pangaea began to split, first into Laurasia (north) and Gondwanaland (south).

Sea floor spreading and plates? — Hess proposed sea floor spreading in 1961. Plate tectonics divides the lithosphere into seven major and some minor plates; the Mid-Atlantic Ridge is the best-known divergent boundary.

India’s journey? — India began moving north about 200 million years ago when Pangaea broke, and collided with Asia about 40–50 million years ago, rapidly lifting the Himalayas.

Rivers? — On gentle gradients streams meander over wide floodplains with natural levees and oxbow lakes; meanders cut into hard rock are called incised or entrenched meanders.

Glaciers? — Cirques — deep basins cut by ice at the heads of glacial valleys — are the most common landforms of glaciated mountains.

Wind and limestone? — Barchans are crescent-shaped dunes whose points face downwind. Karst topography takes its name from limestone country in the Balkans by the Adriatic Sea.

Five layers? — Troposphere, stratosphere, mesosphere, thermosphere and exosphere. The stratosphere (to 50 km) holds the ozone layer, which absorbs ultra-violet radiation; the ionosphere (80–400 km) reflects radio waves back to Earth.

The troposphere? — The lowest layer: about 13 km high on average — roughly 8 km near the poles and 18 km at the equator, where strong convection carries heat highest.

Insolation? — Incoming solar radiation. The Earth is nearest the sun (147 million km, perihelion) on 3 January and farthest (152 million km, aphelion) on 4 July.

Heat budget? — What the Earth absorbs it radiates back, so it neither warms up nor cools down overall; the radiation reflected straight back is the Earth’s albedo.

Temperature inversion? — When air near the ground is cooler than the air above; over polar areas it is normal throughout the year.

Coriolis force? — The Earth’s rotation deflects winds — to the right in the northern hemisphere. It is named after the French physicist who described it in 1844.

Three cells? — General circulation runs in three cells: the Hadley cell in the tropics, the Ferrel cell (surface westerlies) in middle latitudes and the polar cell (polar easterlies). Air rises at the ITCZ.

El Nino? — Warm water appearing off the coast of Peru in place of the cool Peruvian current; it is linked to pressure changes over the Pacific called the southern oscillation.

Four kinds of cloud? — Cirrus, cumulus, stratus and nimbus. Cirrus form high up (8,000–12,000 m), thin and feathery; cumulus look like cotton wool.

Three kinds of rain? — By origin, rainfall is convectional, orographic (relief) or cyclonic (frontal). Relative humidity is greater over the oceans and least over the continents.

Koeppen’s classification? — V. Koeppen related values of temperature and precipitation to the distribution of vegetation. His groups: A tropical humid, B dry, C warm temperate, D cold snow-forest and E cold climates.

Global warming? — The rising concentration of greenhouse gases is the most important human effect on climate and is likely to cause global warming.

The ocean floor? — Four divisions: the continental shelf (the shallowest part), the continental slope, the deep sea plain and the oceanic deeps or trenches, some 3–5 km deeper than the floor around them.

Salinity? — The Indian Ocean averages 35 parts per thousand; the Bay of Bengal is less salty (river water) and the Arabian Sea more (high evaporation). The saltiest: Lake Van (330), the Dead Sea (238), the Great Salt Lake (220).

Tides? — Spring tides come when the sun, moon and Earth are in a straight line — twice a month, at full and new moon; neap tides about seven days later. The world’s highest tides are in the Bay of Fundy, Canada (15–16 m).

Warm and cold currents? — Cold currents usually flow along west coasts in low and middle latitudes; warm currents along east coasts in low and middle latitudes.

Three levels? — Biodiversity — the result of 2.5–3.5 billion years of evolution — is seen at three levels: genetic, species and ecosystem. Areas rich in species are called hotspots.

Threatened species? — The IUCN classifies threatened plants and animals into three categories for their conservation.

According to NCERT, the big bang is generally dated to how long before the present? — 13.7 billion years

Who gave evidence in 1920 that the universe is expanding? — Edwin Hubble

Who revised the nebular hypothesis in 1796? — Laplace

What is the mean thickness of the oceanic crust? — 5 km

To what depth does the mantle extend? — 2,900 km

The upper portion of the mantle, the main source of magma, is called the: — Asthenosphere

Which part of the Earth’s core is liquid? — The outer core

The core is sometimes called the ‘nife’ layer because it is mostly made of: — Nickel and iron

Between what distances from the epicentre lies the shadow zone of both P and S waves? — 105° and 145°

Who put forward the continental drift theory in 1912? — Alfred Wegener

Pangaea first broke into which two landmasses? — Laurasia and Gondwanaland

Who proposed the hypothesis of sea floor spreading in 1961? — Hess

Into how many major plates is the Earth’s lithosphere divided? — Seven

Which is the best-known example of a divergent plate boundary? — The Mid-Atlantic Ridge

About when did India collide with Asia, lifting the Himalayas? — 40–50 million years ago

What is the most common landform of glaciated mountains? — Cirque

Crescent-shaped sand dunes with their points facing downwind are called: — Barchans

Karst topography is named after a limestone region in: — The Balkans, by the Adriatic Sea

Which layer of the atmosphere contains the ozone layer? — Stratosphere

What is the average height of the troposphere? — 13 km

Which layer reflects radio waves back to the Earth? — Ionosphere

When is the Earth nearest the sun (perihelion)? — 3 January

Where is temperature inversion normal throughout the year? — Over polar areas

In the northern hemisphere, the Coriolis force deflects winds to the: — Right

The tropical cell of the general circulation is called the: — Hadley cell

The appearance of warm water off the coast of Peru is known as: — El Nino

Thin, feathery clouds formed at 8,000–12,000 m are: — Cirrus

Which of these is NOT one of the three types of rainfall by origin? — Monsoonal

In Koeppen’s scheme, group B stands for: — Dry climates

Which is the shallowest part of the ocean floor? — Continental shelf

What is the average salinity of the Indian Ocean? — 35 parts per thousand

Which of these has the highest salinity, as NCERT lists them? — Lake Van, Turkey

Spring tides occur when: — The sun, moon and Earth are in a straight line

Where do the highest tides in the world occur? — Bay of Fundy, Canada

In low and middle latitudes, cold ocean currents usually flow along the: — West coasts of continents

Areas rich in species diversity are called: — Hotspots of diversity