Depending upon the shape, volume and rigidity, matter can be
classified into three states, viz. solid, liquid and gas.
a)
Solid: A solid is that form of matter which has
definite mass, shape and volume. Solids are generally hard and righd. Some
common examples are sugar, common salt, a piece of iron, book, etc.
b)
Lifquid: A lifquid is that from of matter which
has definite mass and volume but no definite shape. Liquids take up the shape
of the container in which they are placed. Moreover, liquids have a tendency to
flow. Some common examples of liquids are milk. Water, alcohol. Mercury, etc.
c)
Gas: A gas is that form of matter which has
definite mass but no definite shape and volume., It can assume the shape of the
container due to its mobile nature. It fills the whole of the container in
which it is placed.
Apart from the three states of matter discussed
above, there can be other states of matter as well. Plasma, for example, is a
state of matter containing gaseous ions and occurs only at very high
temperatures. This state is called fourth state of matter. Discussions of
plasma state is beyond the scope of this book.
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Life is a unique and complex phenomenon that distinguishes
the living organisms from non-living things or inanimate things. The origin of
life in the universe is one of the most complicated problems for the
biologists. The problem of creation resolves itself into two aspects: the
origin of the forms of life and origin of life itself. Different biologists
have proposed different theories concerning the origin of life. The major theories
accounting for the origin of life are:
