CBSE Questions for Class 7 Geography Inside Our Earth Quiz 2 - MCQExams.com

Igneous rocks begin the rock cycle, and are therefore called primary rocks. Two major divisions include- volcanic or extrusive rocks that form when magma is ejected from the Earth's crust, and intrusive rocks, which are created below the surface.

Sima is the name for the lower layer of the Earth's crust. This layer is made of rocks rich in magnesium silicate minerals. Typically when the sima comes to the surface it is basalt, so sometimes this layer is called the 'basalt layer' of the crust. The sima layer is also called the basal crust or basal layer because it is the lowest layer of the crust. Because the ocean floors are mainly sima, it is also sometimes called the oceanic crust.

Basalt is a dark-coloured, fine-grained, igneous rock composed mainly of plagioclase and pyroxene minerals. It most commonly forms as an extrusive rock, such as a lava flow, but can also form in small intrusive bodies, such as an igneous dike or a thin sill. It has a composition similar to gabbro. The difference between basalt and gabbro is that basalt is a fine-grained rock while gabbro is a coarse-grained rock.

• A fossil is any preserved remains, impression or trace of any once-living thing (plants, animals etc) from a past geological age. 
• Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood, oil, coal, and DNA remnants. 
• Hence, Remain of plants and animals under the earth are Fossils.
• So, the correct answer is 'Fossils'.