Correct Answer: Option 1 – 1.4%

The time scale is depicted in its traditional form with oldest at the bottom and youngest at the top - the present day is at the zero mark. (See figure below).

The age of the earth is four thousand, six hundred million years old (4,600 million = 4.6 billion), Cenozoic era represent the 65 million years through today. It is approximately 1.41% of the estimated age of the earth

Correct answer: option (4) Cleavage

In above diagram, mineral shows sharp breakages along the crystal face. That is cleavages of the mineral.

Cleavage – Many minerals will, when broken will display a flat plane of breakage which is parallel to a possible crystal face. Cleavage planes are developed along planes of weakness in the atomic lattice and perfection or otherwise of  the cleavage depends upon the relative strength of the bonds in this plane.

Important points to stress include:

Hardness - Hardness is the property of a mineral to resist abrasion. Some minerals can be scratched easily while others are almost impossible to scratch.

Fracture – The breakage of a mineral in a direction other than that of cleavages in

crystalline mineral and in any direction in other minerals.

Streak – Streak of a mineral is its colour in a finely divided state.

Based on these arguments, the rest of the options are incorrect.

Correct Answer: Option 4 – Very coarse texture

Igneous rocks are formed from the cooling of molten (melted) rocks. Igneous rocks may be extrusive on the earth’s surface or intrusive into the rocks forming the crust of the earth. The molten rock material below the earth is known as magma and when it comes to the earth surface is known as lava.

Pegmatite-

A very coarse-grained intrusive igneous rock having a grain size of 3cm or larger, with crystals occasionally reaching a meter or so in length; very rarely, lengths of some ten meters or so have been recorded.

Above diagram shows, very coarse grained texture. Normally very coarse grained textures are formed due to the slow cooling of magma. To cool very slowly, temperature gradient should be very low. That is difference between temperature of the magma and temperature of the surroundings is low. Magma has high temperature and to form large crystals (coarse grained texture) surrounding temperature should be that much of high. As the temperature below the earth surface is very high, molten rock materials cools slowly, taking ten’s of thousand of years to cool and formed very coarse grained Pegmatite.

Correct Answer: Option 3 – Gneiss

Gneiss is a banded rock formed during high-grade metamorphism. When the grade of metamorphism is very high, foliation is the commonest structure of the crystalline rocks; gneisses and schist of various kinds are the predominant rock types. A gneiss is thus essentially a banded or streaky rock in which the layers of differing mineral composition are relatively thick. Gneissose banding consist of more –or less regular alternations of schistose (Schist) and granulose (Granulite) bands. The schistose layers consist of micas and/or amphiboles. (Pyroxene is a rather rare constituent.) The granulose bands are essentially quartzo-feldspathic and may or may not show a preferred orientation. As the layers become thinner, gneiss grades into schist, in which the layers are extremely thin. Gneisses are generally fairly coarse –grained rocks.

Important points to stress include:

• Slate – Low grade regionally metamorphosed, argillaceous rocks which have developed a well marked cleavage but have suffered little recrystallisation, so that the rock is very fine grained.
• Dunite – An ultra basic, mono-mineralic rock consisting of more or less pure olivine.
• Quartzite –Sandstone when metamorphosed, turns into a massive rock called quartzite in which the original sand grains and the silica cement have recrystallized to new quartz grins.

Based on these arguments, the rest of the options are incorrect.

Correct Answer: Option 4 – Explosive eruption of lava from a volcano

Pumice rocks are extrusive igneous rocks meaning it is formed by volcanic eruptions on the surface and typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. They are generally produced from volcanoes whose lava is of a viscous type (less viscous lava produces the characteristic lava flows).

This igneous rock is light and porous, containing a network of gas bubbles in volcanic glass and minerals. Pumice has an average porosity of 90%, and initially floats on water. Pumice is commonly pale in color, ranging from white, cream, blue or grey, to green-brown or black. Pumice is a common product of explosive eruptions and commonly forms zones in upper parts of silicic lavas. It produced in very large quantities and may accumulate as lumps or as abraded fragments of pumice called shards. .

Based on these arguments, the rest of the options are incorrect.