Defence GK Questions 2026

The crust is the outermost and thinnest layer of the earth and is of two kinds. The continental crust, made largely of lighter granitic rock rich in silica and aluminium, averages about thirty kilometres in thickness and reaches about seventy kilometres under young fold mountains such as the Himalaya.

Plate tectonics, propounded in 1967, holds that the lithosphere is broken into seven major plates and a number of minor ones that move over the plastic asthenosphere.

Near Easter Island in the South Pacific the rise spreads at more than fifteen centimetres a year, the highest rate measured, while the Arctic Ridge in option A has the slowest rate of less than two and a half centimetres a year.

It lies between South America and the Pacific plate and is one of the well known minor plates, along with the Cocos, Arabian, Philippine, Caribbean, Juan de Fuca, Scotia, Caroline and Fuji plates.

Along the San Andreas Fault the Pacific plate and the North American plate slide horizontally past each other.

The Indian plate moved northwards and met the Eurasian plate. Both carry light continental crust, so neither could sink far into the mantle; instead the sediments of the Tethys Sea lying between them were compressed, folded and thrust upwards to form the Himalaya, and the collision is still going on…

After the detailed mapping of the ocean floor during and after the Second World War revealed mid-oceanic ridges, deep trenches and a surprisingly thin cover of sediment, Hess proposed in 1961 that molten material rises along the ridge, forms new ocean floor and pushes the older floor away on both…

When Pangaea began to break about two hundred million years ago, it parted into a northern mass called Laurasia or Angaraland and a southern mass called Gondwanaland, and the long narrow Tethys Sea lay between the two.

Wegener attributed the horizontal movement of the continents to the pole-fleeing force, which arises from the rotation of the earth and the bulge of the equator, and to the tidal force, which arises from the attraction of the moon and the sun.

Wegener held that about two hundred and fifty million years ago all the land of the earth lay together as one mass, Pangaea, and that one enormous ocean, Panthalassa, surrounded it.

Wegener, a German meteorologist and climatologist, put forward the continental drift theory in 1912 and developed it in his book The Origin of Continents and Oceans; he argued that all the continents once formed a single landmass, Pangaea, which broke up about two hundred million years ago.

Sphagnum is a bog moss, a bryophyte, whose dead cells hold many times their own weight of water; in waterlogged and acidic bogs its remains decay only partly and pile up as peat, which is cut, dried and burnt as fuel and is also used in nurseries to keep soil…

An angiosperm shows double fertilisation: of the two male gametes brought by the pollen tube, one fuses with the egg to give a diploid zygote, and the other fuses with the two polar nuclei of the central cell.

The word itself means naked seed: the ovules are not enclosed in an ovary, so after fertilisation the seeds lie exposed on the surface of the scales of a cone and no fruit is formed.

It is the only surviving species of its order, has remained almost unchanged for many millions of years and is known from fossils of the age of the dinosaurs, which is why it is called a living fossil; it is a gymnosperm with fan-shaped leaves, grown widely as an ornamental…

Besides its normal roots, Cycas bears small branched roots that grow upward near the surface and look like coral; these coralloid roots hold cyanobacteria such as Anabaena and Nostoc, which fix atmospheric nitrogen and supply it to the plant.

Brown algae of the class Phaeophyceae contain chlorophyll a and c along with the xanthophyll pigment fucoxanthin, and because fucoxanthin masks the green chlorophyll the plant looks olive green to deep brown; Laminaria, Sargassum, Fucus, Ectocarpus and Dictyota are examples, and many of them bear air bladders that keep the…

The green algae owe their colour to chlorophyll a and chlorophyll b, which are not masked by any other pigment; Chlamydomonas, Volvox, Spirogyra, Ulothrix and Chara belong here, and their stored food is starch.

Agar is obtained chiefly from Gelidium and Gracilaria, members of the Rhodophyceae, and it is used to prepare the solid media on which microbes and plant tissues are grown, as well as in jellies and ice cream.

Ferns and their relatives, such as Selaginella, Lycopodium, Equisetum, Pteris, Adiantum and Marsilea, are the first plants with xylem to conduct water and minerals and phloem to conduct food, and the first with a true root, stem and leaf; for that reason they are also called the vascular cryptogams.