About 3000 years ago people believed that the Earth was flat. But people wondered why ships disappeared at the horizon. Sailors too returned from journeys and were proof that ships did not fall off the edge of the Earth. The simplest explanation was: the Earth must be round. The final proof came in the year 1522 after the expedition of Ferdinand Magellan, who was the first to sail around the Earth.
Caves and mines go only up to 1-2 km inside the Earth. Even the deepest wells of the world, such as the one 12 km deep in the Russian Kola Peninsula or the 9-km-deep one in the Upper Palatinate, hardly scratch the Earth’s crust. One can ‘look’ deep inside the Earth in the aftermath of earthquakes or by creating nuclear explosions. The explosions generate sound or seismic waves. They also throw off rock particles. By measuring their intensity and timings, scientists discover the composition of the Earth’s interiors.
Like an onion, the Earth has several layers. The outermost layer, the Earth’s crust, has an average depth of about 40 km. As compared with the diameter of the Earth, which is around 12,700 km, the Earth’s crust is very small. It is primarily made up of solid rocks. Below the crust is the mantle, reaching to a depth of about 2900 km. Due to the heat inside the Earth, the mantle consists of solid and molten rocks. Below the mantle is the core, made up of iron and nickel. The deeper one travels inside the Earth, the hotter it is. The temperature in the core is between 4000 and 5000 degree Celcius.
It has been known for more than 2000 years that the Earth is round, but we were able to actually see this much later only when we flew into space. The knowledge why we do not fall off from the Earth is much more recent. A journey as described by author Jules Verne in his book Journey to the Center of the Earth was, after all, impossible. Only one thing was known: the Earth is made up of soil, rocks, and water. Today, we know that the Earth is also surrounded by an air cover called the atmosphere.
Butterflies protect themselves from predators through the plants to protect themselves from enemies. This has led to the evolution of bright colours in unpalatable butterflies.
Camouflage is another technique that butterflies use to escape from their enemies. Camouflage is the technique of blending with the colour of the surrounding to hide from enemies.
We all might have seen butterflies that look like the leaf of a tree, or a twig in a branch. Such varieties as the oak leaf butterfly and autumn leaf butterfly use this camouflage technique.
Some others have deimat-ic behavior, such as waving their front ends marked with eyespots as if they were snakes.
Butterflies are very good fliers. They have two pairs of large wings covered with scales. Their wings are attached to the thorax. Veins support the wings, and ensure the blood supply.
Butterflies can fly only if their body temperature is above sudden landings. Speed varies among butterfly species. Poisonous varieties are slower than non-poisonous varieties.
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