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1. 2. The atmosphere, hydrosphere, lithosphere, mantle and the core are the five parts that make up the
earth.
The atmosphere, the first part, is a gaseous envelope that surrounds the solid body of the planet. It
has a thickness of more than 1100 kilometers; however, about half its mass is concentrated in the
lower 5.6 kilometers.
The hydrosphere, the second part, is the layer of water that, in the form of the oceans, covers
approximately 70.8 per cent of the surface of the earth. Although it chiefly consists of the oceans,
technically it includes all water surfaces in the world, including inland seas, lakes, rivers, and
underground waters. The average depth of the oceans is 12,447 feet, more than five times the
average height of the continents. The mass of the oceans is approximately 1.35 quintillion metric tons,
which is the equivalent of 1/4400 of the total mass of the earth.
The third, fourth and the fifth layers, that is the lithosphere, mantle and the core, are largely solid.
The lithosphere, consisting mainly of the cold, rigid, rocky crust of the earth, extends to depths of 100
kilometers. The rocks of the lithosphere have an average density of 2.7 and are almost entirely made
up of 11 elements, which together account for about 99.5 per cent of its mass. The most abundant is
oxygen, which accounts for about 46.60 percent of the total. Other elements include silicon,
aluminium, iron, calcium, sodium, potassium, magnesium, titanium, hydrogen and phosphorus. In
addition, eleven other elements are present in trace amounts of 0.1 to 0.02 per cent.
The lithosphere comprises of two shells, the crust and the upper mantle. These are divided into a
dozen or so rigid tectonic plates. The crust itself is divided into two parts. The upper crust is referred
to as Sial and the lower crust is known as Sima. The upper crust, which comprises of the continents, is
made up of igneous and sedimentary rocks whose average chemical composition is similar to that of
granite and whose density is about 2.7. The simatic or lower crust, which forms the floors of the ocean
basins, is made of darker, heavier igneous rocks such as gabbro and basalt.
The mantle and core are the heavy interior of the earth, making up most of the earth’s mass. The
mantle extends from the base of the crust to a depth of about 2900 kilometers.
The upper mantle is separated from the crust above by a seismic discontinuity, called the Mohorovicic
discontinuity, or simply, Moho. A weak zone, known as the asthenosphere, separates it from the lower
mantle below. The upper mantle is composed of iron and magnesium silicates, as typified by the
mineral olivine. The lower part may consist of a mixture of oxides of magnesium, silicon, and iron.
Researchers say that the core has an outer shell which is about 2225 kilometers thick. Studies have
shown that its outer surface has depressions and peaks, the latter forming where warm material rises.
In contrast, the inner core, which has a radius of about 1275 kilometers, is solid. Both core layers are
said to consist largely of iron, with a small percentage of nickel and other elements. The temperatures
in the inner core may be as high as 6650°C or 12,000°F.

2. 1. In physics and systems theory, the superposition principle [1], also known as superposition
property, states that, for all linear systems, the net response at a given place and time caused by two or
more stimuli is the sum of the responses which would have been caused by each stimulus individually. So
that if input A produces response X and input B produces response Y then input (A + B) produces
response (X + Y).
Mathematically, for a linear system, F, defined by F(x) = y, where x is some sort of stimulus (input)
and y is some sort of response (output), the superposition (i.e., sum) of stimuli yields a superposition of
the respective responses:
The principle of faunal succession, also known as the law of faunal succession, is based on the
observation that sedimentary rock strata contain fossilized flora and fauna, and that these fossils succeed
each other vertically in a specific, reliable order that can be identified over wide horizontal distances. A
fossilized Neanderthal bone will never be found in the same stratum as a fossilized Megalosaurus, for
example, because neanderthals and megalosauruses lived during different geological periods, separated
by many millions of years. This allows for strata to be identified and dated by the fossils found within.
This principle, which received its name from the English geologist William Smith, is of great importance in
[1]
determining the relative age of rocks and strata.