(a) "Evidences from palaeomagnetism and sea floor spreading have validated that continents and ocean basins have never been…

(a) Palaeomagnetism and sea floor spreading as evidence of mobile continents

Wegener's drift lacked a mechanism, and two lines of evidence from the 1950s and 1960s supplied it.

(i) Palaeomagnetism. Iron-rich minerals such as magnetite in cooling lava record the direction of the Earth's field at the time, once they pass below the Curie point. Rocks of different ages on one continent point to different pole positions, which plot as an apparent polar wandering path. Since the pole cannot be in two places, the curves of Europe and North America, which are separate but come together when the Atlantic is closed, show that the continents moved. The same rocks also give their palaeolatitudes, such as India's northward passage from the southern hemisphere.

(ii) Sea floor spreading. Harry Hess proposed that new basaltic crust forms at mid-ocean ridges by upwelling magma and moves away on both sides, to be consumed at trenches. Vine, Matthews and Morley showed that the crust records reversals of the field, so symmetrical stripes of normal and reversed polarity lie parallel to the ridge.

(iii) Supporting data. Ocean drilling shows the basalt growing older, and the sediment thicker, away from the ridge, and no ocean floor is older than about 180 million years. Spreading rates range from 2 to 5 cm a year along the Mid-Atlantic Ridge to over 15 cm a year on the East Pacific Rise.

Together they show that ocean basins open and close, and that continents have never been stationary.

(b) Anticyclones: characteristics and weather

An anticyclone is a system of high pressure with closed isobars, weak gradients and winds spiralling outward, clockwise in the Northern Hemisphere and anticlockwise in the Southern.

(i) Characteristics. Air subsides from aloft and warms by compression, so humidity falls and cloud dissolves. Winds are light and there is usually a calm centre. The systems are large and slow, and they form in two ways: dynamically, in the subtropical belts from the descending Hadley cell, and thermally, over cold continents such as the Siberian High and the Canadian High.

(ii) Weather. Skies are clear, dry and stable. In summer this brings heat waves and drought, as in a blocking high over Europe. In winter the clear nights cool the ground by radiation, producing temperature inversions, frost, radiation fog and smog, as over the Indo-Gangetic plain in December and January.

(c) Generation of ocean currents and effects on coastal climates in the Pacific

Currents arise from several causes:

(i) Planetary winds. The trades and westerlies push surface water by frictional drag, and the Coriolis force deflects it, producing gyres.

(ii) Density differences. Water that is colder or saltier sinks and spreads, while warmer water rises and flows to replace it.

(iii) Land and bottom relief. Continents deflect the flow and form western boundary currents, while the ocean floor steers them. Tides and differences in sea level also contribute.

Effects in the Pacific.

(i) Kuroshio. This warm current along Japan raises temperature and rainfall, and feeds typhoons. The cold Oyashio meets it near Japan and gives fog and rich fisheries.

(ii) California Current. The cold current keeps the US west coast cool and dry, with summer fog and Mediterranean aridity.

(iii) Peru (Humboldt) Current. It brings cold, nutrient-rich upwelling, rich anchovy fisheries, and the extreme dryness of the Atacama.

(iv) East Australian Current and ENSO. The warm East Australian Current adds moisture to eastern Australia. In El Niño years the Peru Current weakens, warm water replaces it, and heavy rain falls on the normally arid Peruvian coast while Australia and India often see drought.