ORIGIN OF EARTH

ORIGIN OF EARTH

             Earth is one of the 9 planets (8 excluding Pluto) orbiting the SUN in the Solar System.

           The Universe is composed of several Galaxies. Our solar system is part of Milky way galaxy which is disk shaped with about 1, 00,000 million stars of varying sizes. Our solar system consists of 9 planets and 31 satellites, a belt of asteroids

THEORIES

•      NEBULAR HYPOTHESIS

•      PLANETESIMAL HYPOTHESIS

NEBULAR HYPOTHESIS

•      Solar system formed through the condensation of a nebula which once encircled the Sun

•      The outer planets formed first, followed by Mars, the Earth, Venus, and Mercury. This hypothesis suggests a sequential origin from outermost planet to innermost.

•      As per this hypothesis, Mars evolved earlier than the Earth. This hypothesis is widely accepted to explain origin of different planets

PLANETESIMAL HYPOTHESIS

•      A catastrophic hypothesis, proposed by Thomas Chamberlin and Forest Moulton (1905), in which the planets of the Solar System are seen to arise from an encounter between the Sun and another star.

•      In this scenario, the gravity of the passing star tears a succession of bolts from the solar surface.

•      Bolts coming from the side nearer the star are thrown out to distances comparable with those of the giant planets, while those from the far side of the Sun are ejected less violently to the distances of the terrestrial planets.

 

Table 1.Radius, distance from sun and revolution period

S.No	Planet	Radius (km)	Distance from sun(m.k)	Revolution period (day)
1	Mercury	2439	57.9	88
2	Venus	6052	108.2	245
3	Earth	6378	149.4	365.25
4	Mars	3397	227.9	687
5	Jupiter	71398	778.3	4333
6	Saturn	60000	1427	10743
7	Uranus	23620	2870	30700
8	Neptune	24300	4496.5	60280
9	Pluto	1150	5970	90130

Table 2.Geological Time Scale of Earth – Development of Life

Era	Period	Age (m.Yr)	Organism
Archean	Archean	> 3500	Lifeless
Precambrian	Precambrian	-do-	Soft bodied plant & animals
Palaeozoic	Cambrian	500	Algae and shell bearing molluscus
	Ordovician	400	Molluscus & sea weeds
	Silurian	360	Land plants & breathing land animals
	Devonian	320	True fishes and  ampibians
	Carboniferous	280	Coal forming materials , non flowering plants
	Permian	246	Reptiles
Mesozoic	Triassic	235	Marine life & reptiles
	Jurassic	185	Dinosours
	Cretaceous	139	Many plants & fishes
Cenozoic	Tertiary             Eocine	20	Mammals
	Myocine	29	Mammals
	Pliocine	10	Mammals
	Quartanary
	Plistocine	01	Mammals
	Recent time		Mammals

Table 3.Average composition of Earth’s crust (% by weight)

Non - metallic	Oxygen	O2-	46.60%	74.32%  (3/4th)
	Silica	Si4+	27.72%
Metallic	Aluminium	Al3+	8.13%	1/4th  of the total
	Iron	Fe2+	5.00%
	Calcium	Ca2+	3.63%
	Sodium	Na+	2.83%
	Potassium	K+	2.59%
	Magnesium	Mg+2	2.09%
	Others	-	1.41%

Eight elements are abundant – 98.6%

INTRODUCTION TO SOIL SCIENCE

INTRODUCTION TO SOIL SCIENCE         THE CONCEPT OF SOIL

SOIL – SOUL OF INFINITE LIFE

-J.S. KANWAR

The term soil is derived from the latin word ‘solum’ which means floor.

For a layman, soil is the dirt or debris on the surface of the earth. To a mining engineer the soil is the delaines covering the rocks (or) minerals that he must quays. To a highway engineer the soil may be the material on which a roadbed is to he placed. To an agriculturist soil is a natural medium for plant growth. The farmer makes a living from the soil and he is forced to pay more alteration to its characteristics. To the former the soil is more than useful it is indispensable.

The concept of soil has been changing with the accumulation of more data and knowledge. Whitney (1892) developed the concept of soil as a nutrient bin, ie, they hold all the nutrient required for the plant growth. Geologists considered soil to be the product of rock
weathering.

Ruffin (1968)s considered soil as a mixture of earth’s uppermost mantle of weathered

rock and organic matter.

According to hilgend (1992), “Soil is more or less a loose and friable material இன் which plants by means of their roots finds nourishment as well as other condition of growth.

Soil Is a Natural Body

The concept of soil as a natural body originated from its ability to produce and sustain

crop.

Justies von liebig (1840) in his famous publication “Chemistry applied to Agriculture

and physiology” put forward the theory mat plants assimilate mineral nutrients from soils. He is called as father of agricultural chemistry.

The fundamental principles of soil science were first laid down by V.V.Dokuchaev(father of soil science) and his students in VSSR in 1879. According to them, soils are தி surface mineral and organic formations, always more or less coloured by humans. According
to them soils are formed by weathering of rocks and minerals.

Soil Is a Three Dimensional BodySoil should be recognized as three dimensional body having length, breadth anddepth. For a through study of soils, the study surface soil will not be sufficient. We have todig a pit (soil profile) and studying the physical, chemical and biological characteristics.

Scope of Soil Science

Soil Science has six well defined and developed disciplines. Scope of soil Science is reflected through these disciplines.

Soil Science : The science dealing with soil as a natural resource on the surface of the earth, including Pedology (soil genesis, classification and mapping) and the physical, chemical and biological and fertility properties of soil and these properties in relation to their management for crop production .

1. Soil fertility: Nutrient supplying properties of soil

2. Soil chemistry: Chemical constituents, chemical properties and the chemical reactions

3. Soil physics: Involves the study of physical properties

4. Soil microbiology: deals with micro organisms, its population, classification, its role in transformations

5. Soil conservation: Dealing with protection of soil against physical loss by erosion or against chemical deterioration i.e excessive loss of nutrients either natural or artificial means.

6. Pedology: Dealing with the genesis, survey and classification

Soil – Definitions

Joffe (1936): Soil is a natural body of mineral and organic constituents differentiated into horizons usually unconsolidated, of variable depth which differs among themselves as well as from the underlying parent material in morphology, physical makeup, chemical properties and composition and biological characteristics.

SSSA (1970): (i) The unconsolidated mineral matter on the surface of the earth that has been subjected to and influenced by genetic and environmental factors of parent material, climate (including moisture and temperature effects), macro and microorganisms and topography, all affecting over a period of time and producing a product, that is “SOIL” that differs from the material from which it is derived in many, physical, chemical, biological and morphological properties and characteristics.

(ii) The unconsolidated mineral material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.

V.V.Dokuchaev(1900): "Soils are applied solely to those superficial or nearly superficial horizons of rocks, that have been more or less modified naturally by the interaction of water, air and various kinds of organisms, either living or dead; this being reflected in a certain manner in the composition, structure and colour of such formations. Where this conditions are absent, there are no natural soils, but either artificial mixtures or rock”

Buckman and Brady: “Soil may be defined as ”A dynamic natural body on the surface of the earth in which plants grow, composed of mineral and organic materials and living forms”.

Approaches of Soil Study

Two Concepts: One treats soil as a natural body, weathered and synthesized product in nature while other treats soil as a medium for plant growth.

Pedological Approach: The origin of the soil, its classification and its description are examined in Pedology. (from Greek word pedon, means soil or earth). Pedology is the study of soil as a natural body and does not focus on the soil’s immediate practical use. A pedologist studies, examines and classifies soil as they occur in their natural environment.

Edaphological Approach: Edophology (from Greek word edaphos, means soil or ground) is the study of soil from the stand point of higher plants. Edaphologists consider the various properties of soil in relation to plant production. They are practical and have the production of food and fibre as their ultimate goal. They must determine the reasons for variation in the productivity of soils and find means for improvement.