Different types of landscapes such as plains, wide valleys, gorges, dunes, rounded hills, and rugged ridges are formed largely by the forces of water, wind, and moving ice, which nibble, sharpen, and polish the surface of the Earth. Experts call this process ‘erosion’. These forces are much stronger than they appear. For instance, flowing water can move whole blocks of rock. The largest bits of rock thus eroded later become sand, which may be fine or coarse in texture and red, white, or grey in colour. Human beings also contribute to the constant changes taking place on the face of landscapes.
Universe, cosmos, and space mean the same - the space all around us and what it contains as far as we can see and think. We do not know whether the space is endless or is finite. If there were a border, what would be behind it? The astronomers are still dealing with the question of the origin of the universe and its end. An important factor to support the Big Bang theory of the origin of the universe is the ‘cosmic background radiation’, which was discovered in 1964. We still wonder whether there are intelligent civilizations somewhere in space - and are looking for them.
Unlike climate, weather depends on the seasons and can also change anytime. Meteorologists predict in the evening how the weather will be the next day. The weather is driven by the sun, which heats up the ground and the water surfaces. Evaporated water creates clouds from which thunderstorms build up, and the ensuing bursts of thunder and lightning make us flinch. Every time a cyclone hits the tropical regions, lashing rain sends people running for cover.
There have been many ice ages in the entire history of the Earth. During these cold phases, the average temperature of the Earth dropped 5°C below the normal level and the Polar Regions were completely covered with ice. The last big cold period, known as ‘ice age’, ended around 10,000 years ago, with the thawing of the large glaciers that were several kilometres thick. It is not yet clear what causes an ice age. Researchers believe that the sudden change in the Earth’s climate may be a result of some sort of a disturbance in the orbit of the Earth or a reduction in the heat of the sun reaching the Earth. Another theory suggests that, prior to the ice age; the continents might have changed positions and blocked or reduced the flow of warm currents from the equator to the poles, and thus allowed ice sheets to form in the region.
Hot or cold ocean currents affect the climate of the landmasses along their course. The Agulhas current, for instance, long prevented Portuguese sailors from reaching India. Ocean currents also affect temperatures all across the world. The current that brings warm water up the North Atlantic Ocean to the north-west European shores stops ice from forming near the coasts and blocking ships from entering and exiting ports. In northern Canada, cold ocean currents freeze the soil all through the year. The cold Benguela current that runs off the coast of Namibia has created one of the driest deserts of the world - the Namib Desert. This current does not allow the sea water to evaporate, and thus prevents the formation of clouds in the local sky.
The trade wind is a wind that blows throughout the year in the tropics, a broad belt around the equator. In the northern hemisphere, it blows from the northeast to the equator, and in the southern hemisphere, it blows from the southeast to the equator. The sun, being directly overhead, is very strong and heats up the air in the equatorial region. The warm air automatically rises up, reducing the atmospheric pressure and allowing the surrounding air to flow in towards the equator. This flow of air is called the ‘trade wind’.
While the weather changes every day and a hot and humid day can be followed by a rainy one, the climate of a region remains the same for a long time. Thus, the summer season at the North Sea is generally cooler than in Freiburg and the winter season is rather cold and damp and not as snowy as in the Alps. The climate is driven by the sun, which heats up the air and gives rise to winds such as the trade wind. The oceans and the ocean currents also affect world climate, an instance of which can be seen in the way things turn topsy-turvy due to occurrence of ‘El Nino’. The climate also undergoes long-term changes.
The icebergs in the North Atlantic are large pieces of ice that have broken off from the glaciers of Greenland. Since frozen water is lighter than liquid water, the broken pieces float as icebergs on the sea. They are pointy and often interspersed with debris. In contrast, the icebergs in the South Atlantic are mostly flat. They are broken pieces of the flat sea ice, which surrounds the Antarctic. Icebergs can float for thousands of kilometres before they melt. Only one-ninth of an iceberg stays above the water. If the part above the water is 100 m high, then the part below is 800 m deep.