My Science School

A crater is formed when a small space body such as an asteroid or a meteor collides with the surface of a planet or a moon. The Earth and the Moon both have many craters but the chances of Earth being hit by a space body is far more than the Moon due to its large size. However, despite its size, the moon has thousands of craters while we know of only 180 on Earth. Why?

Both Earth and Moon have been hit many, many times by small space bodies throughout their existence. However, the Earth has processes that can erase almost all evidence of a crater, unlike the Moon. The three processes are:

Erosion

The Earth has water (rain, floods), plants (break up earthen materials) and weather (wind, etc.) which can act together and erode over a period of time erosion can break a crater down to almost nothing.

The Moon on the other hand has no erosion because it has no atmosphere. This means it has no wind, no water and definitely no plants that can erode its surface and remove marks off its surface.

Tectonics

Tectonics are processes that cause Earth’s surface to form new rocks and get rid of old ones due to their shifting around over millions of years. Because of this, Earth’s surface is recycled many times throughout its existence, leaving it with very few rocks that are as old as those on the Moon. Since the Moon has not had tectonics for billions of years, it has a lot of time to stay put.

Volcanism

Volcanic flows on Earth can cover up impact craters. This is also the way may impact craters get covered in other parts of the solar system. While the Moon had large volcanic flows in the past that covered up most of its craters, it hasn’t had volcanism in nearly three billion years!

 

Picture Credit : Google

It is, indeed. What we are seeing is merely a trick of the eye or an optical illusion.

In physics, this is referred to as total internal reflection. The complete reflection of a ray of light within a medium (say water or glass) from the surrounding surfaces back into the medium is defined as total internal reflection. If the angle of incidence is greater than a certain angle, referred to as critical angle, then total reflection occurs.

An everyday example

What we see is an example of total internal reflection, happening when a swimmer dives into the swimming pool. The picture, taken near the shallow end of the swimming pool, shows a broad bubble where the swimmer has just dived in, which would also mark the water surface. While the lower portion of her reflection distorted because of the dive, the rest of the water surface is calm and hence the remaining portion of her body and the tiled bottom of the pool can be seen in the reflection at the top of the picture.

Try to notice this is the next time you take a look at a fish tank standing beside it and bending to have your eyes below the water level.

 

Picture Credit : Google

Apart from planets, stars and moons, there are several small solar system bodies such as asteroids and comets in space. These are usually speeding through space. Sometimes, a larger body such as a planet or a moon can come in their way. When this happens, these extremely fast spacebodies crash into the surface of the larger space body and create a depression called impact crater.

For an object to be able to create an impact crater, it needs to be travelling at a speed of many thousand kilometres per hour. No matter how hard or tough the surface of a planet or the moon is, when a superfast object collides with it, it will definitely leave an impact by vaporizing the area and creating enormous shockwaves through the ground, which can melt and recrystallise rock.

The size and shape of a crater depends on factors such as mass, density and velocity of the impacting object, and the geology and velocity of the impacting object, and the geology of the surface it strikes. Many planets and moons in our solar system have impact craters.

Two of the famous impact craters on Earth are:

Meteor Crater

Also known as the Barringer Crater in Arizona, the U.S., this is the first crater formed by an extraterrestrial impact to be identified. It formed nearly 50,000 years ago from a meteorite that may have been up to about 150 feet wide travelling at more than 45,000 kmph.

Vredefort crater

Situated in South Africa, this is the largest-known impact crater on Earth. It is nearly 300 km in diameter and over two billion years old. However, due to erosion over time, it is difficult to see the crater. What remains today are geological structures at its centre known as the Vredefort Dome or Vredefort impact structure.

 

Picture Credit : Google

A small amount of scandium in an alloy makes it much stronger and reduces its weight. For this reason, scandium-aluminium alloys are used to make very strong and very expensive sports equipment, including bicycle frames and baseball bats.

A little bit of scandium is also used in mercury vapour lamps to produce a bright white light that is similar to daylight.

Scandium is a silvery-white metal, which develops a slightly yellowish or pinkish hue when exposed to air. Scandium was discovered by Lars Fredrik Nilson, a Scandinavian in 1876. He found it in the minerals euxenite and gadolinite, which had not yet been found anywhere except in Scandinavia. Apparently, there is much more scandium on the sun and many other stars than here on Earth.

Titanium possesses many desirable qualities that make it a sought-after metal. It is extremely elastic, lightweight, corrosion-resistant and nonmagnetic. Titanium is as strong as steel, but much lighter. It is twice as strong as aluminium. It is nearly as resistant to corrosion as platinum.

            Titanium is used to make money clips used to hold bank notes and even credit cards. The alloys of titanium are used principally in the aerospace industry, where lightness of weight, strength and ability to withstand extremes of temperature are important.

Titanium is used to make alloys with aluminium, molybdenum, manganese, iron, and other metals. Titanium has excellent resistance to sea water, and is used to manufacture the parts of ships that are exposed to saltwater. Titanium paint is extensively used in solar observatories where heat causes poor viewing conditions.

Manganese resembles iron in its appearance, but it is harder than iron and brittle. It is an important component of steel. In fact, 95 per cent of the manganese produced in the world each year is used to make steel! It is also used to form many important alloys.

Apart from making steel, manganese is used to prepare oxygen and chlorine. It is also used to dry black paints. A compound of manganese is used as an additive in unleaded gasoline to reduce engine knocking. Oxides of manganese are used to neutralize the greenish tint of glasses. It was also used in the original type of dry cell battery.

Compounds of manganese were used to colour ceramics and glass since a long time. The brown colour of ceramics is usually the work of manganese. Manganese is occasionally used to make coins as well.

Tungsten is widely used to make the filaments of electric bulbs. But, tungsten is not the only metal that conducts electricity well. There are other metals like gold and silver that are also good conductors of electricity. Then why is tungsten preferred?

Tungsten is not only a good conductor; it also has a very high melting point. In fact, tungsten has the highest melting point, and lowest vapour pressure of all metals. Because of this, the filaments made of tungsten glow more brightly and produce more light without melting, than if they were made of say, silver or copper.

The high melting point of tungsten makes it the ideal metal for making electrical heating coils, cathode ray tubes found in television sets, computer monitors, X-ray tubes and microwave ovens. It is also used to make switches for very high voltage lines.

Cadmium occurs naturally in the Earth’s crust. However, cadmium is a poison and is known to cause cancer and even birth defects. One of the major uses of cadmium is to make rechargeable nickel cadmium batteries. Though there was a steep rise in the use of these batteries over the past few decades, it is being gradually phased out.

Cadmium is used to make specialist alloys. Compounds of cadmium are used to colour paints and ceramic. It is also used as stabilizers that prevent plastics from becoming brittle, and for television and computer screens.

Cadmium is also used as coatings to protect metals such as iron and steel. Metal parts coated with cadmium slide over each other easily; therefore, some parts of cars and aircraft are cadmium coated.

Picture Credit : Google

Remember sacrificial protection that we talked about earlier? That is not the only way to protect iron from corrosion. Zinc, a bluish-white, lustrous metal is also used for protecting iron. Want to know how?

Coating thin layers of zinc on iron or steel can prevent corrosion. This method is known as galvanization. Iron or steel objects are either dipped in molten zinc or electroplated with zinc. Zinc is a reasonable conductor of electricity, and burns in air at high red heat.

The zinc corrodes forming a layer of zinc oxide on the surface of iron which stops air and water reaching the surface of the iron and this is how it prevents rusting. The iron or steel remains rust free while the zinc itself rusts away.

Picture Credit : Google

Emperor Napoleon III had his finest dinner spoons made of aluminium. Why would an emperor make his finest cutlery with a metal as cheap as aluminium? Let us see.

Aluminium is the most abundant metal on the Earth’s crust; it makes up 7 per cent to 8 per cent of the Earth’s crust. But, aluminium is always found in combination with other elements and never found free in nature. Because of this, aluminium was not known to the world for a very long time.

Aluminium became a sensation in the early 19th century when Hans Christian Oersted, a Danish chemist produced the metal in tiny amounts. However, it was very expensive to produce, and therefore considered a luxury item, affordable only by very rich people like emperors!

By the late 19th century however, scientists developed the technique of obtaining aluminium from aluminium oxide. This increased the availability of the metal and led to the era of inexpensive aluminium.

Nickel has got a unique name; it is the only metal named after a devil. Like cobalt, the word nickel comes from a German word ‘kupfernickel’, meaning ‘Old Nick’s copper’. This term too was used by German miners.

Their efforts to obtain copper from an ore that seemed copper ore did not meet with success. Instead of copper, all they could get was slag. The miners believed the devil or ‘Old Nick’ as they called him, was playing a trick on them and called it kupfernickel. Nickel was eventually discovered from this slag.

Nickel was discovered in 1751. Axel Fredrik Cronstedt of Sweden was attempting to extract copper from the mineral niccolite. To his surprise, he got a silvery-white metal, instead of the copper. He named the new metal nickel. But before all this, an alloy of copper, nickel and zinc was used in China as far back as 235 BC for utensils and other metal ware.

Cobalt-60 is hard, brittle and has a bluish tint. Its properties are similar to that of iron and nickel and remains in solid state in normal conditions.

It can be magnetized just like iron. It is radioactive; its nucleus can break apart and give off radiation. For this reason, it is used in radiotherapy in hospitals. It is also used in some medical devices for the precise treatment of deformities of blood vessels and brain tumours that cannot be operated upon. It is useful in the sterilization of medical equipment too.

Certain food products including spices are often sterilized using cobalt-60. The powerful gamma rays kill bacteria without damaging the product or making it radioactive.

Do you know that radiography is used to detect the flaws of structures and equipment made of metals? This process is known as industrial radiography; cobalt-60 is used for this as well.

Humans have been using compounds of cobalt since at least 1400 BC. We already know that it was used in paints, pottery and glassworks. Different kinds of compounds of cobalt are used as pigment in pottery, glass enamels and paints. This element forms an essential part of Vitamin B12 and is essential in small amounts for proper nutrition.

Cobalt is used to make super alloys. Super alloys are resistant to corrosion or rusting and retain their properties at high temperatures. They are used in jet engine parts and gas turbines. To make super alloys metals like iron, cobalt, or nickel are mixed with small amounts of other metals, such as chromium, tungsten, aluminium, and titanium.

Because of its defined magnetic properties, cobalt is used to make magnets. It is also used to make batteries; lithium cobalt oxide is used to make lithium-ion batteries. It is also used for electroplating because of its attractive appearance.

Platinum is one of the most wanted metals in the world. People go crazy about platinum because it has a wide variety of industrial applications. Platinum jewellery is popular around the world. Most of the catalytic convertors in the world use platinum. In fact, 70 per cent of the world supply of platinum is used to make jewellery and catalytic convertors.

Platinum is used in fuel cells, computers and in the petroleum industry. It is also used for electrical contacts, corrosion resistant apparatus, and in dentistry. Cisplatin, a compound of platinum, is an important anticancer drug.

Nowadays, platinum jewellery is considered fashionable and more prestigious than gold. Platinum is stronger than gold; even the smallest piece of platinum can maintain its shape for a longer period. The strength of platinum makes it ideal for making jewellery. Platinum in jewellery is usually 95 per cent platinum alloyed with copper and other platinum group metals.

Picture Credit : Google

The word cobalt was first used towards the end of the fifteenth century. The German word Kobold means ‘goblin’ or ‘evil spirit’. The miners used this word to describe a mineral that was very difficult to mine and also posed health hazards.

When the mineral was heated, it gave off an offensive gas that caused illness. The gas that affected the miners was arsenic trioxide which is often present with cobalt in nature.

In 1735, a Swedish chemist, Georg Brandt analyzed a dark blue pigment found in copper ore. Brandt demonstrated that the pigment contained a new element, later named cobalt. But cobalt-based blue pigments have been used to make jewellery and paints since a very long time. Remember the cobalt blue colour in your oil paint set? The name comes from this metal.

Cobalt is usually produced by reductive smelting. It is one of only three naturally occurring magnetic metals.

Picture Credit : Google