The word 'Environment' is derived from the French word 'Environner' which means to encircle, around or surround. The biologist Jacob Van Uerkal (1864-1944) introduced the term environment in ecology. As given by Environment Protection Act 1986, Environment is the sum total of land, water, air, interrelationships among themselves and also with the human beings and other living organisms. 

A) Definitions of Environment : 

1. Douglas and Holland(1947):  Environment is a word which describing the aggregate, all of the extrinsic (external) forces influences and conditions which affect the life, nature, behaviour and the growth, development and maturation of living organisms.

2. Woodworth and Marques(1948): Environment covers all the outside factors that have acted on the individual since he began life.

3. Boring : According to Boring "A person's environment consists of the sum total of the stimulation which he receives from his conception until his death".

B) Principles of Environmental Science:

1. Interdisciplinary Approach: Environmental science draws on knowledge from various scientific disciplines, including biology, chemistry, physics, geology, ecology, and sociology, to study the environment comprehensively.

2. Sustainability: The principle of sustainability emphasises meeting the needs of the present without compromising the ability of future generations to meet their own needs. Environmental science seeks to promote sustainable practices that conserve natural resources and protect ecosystems. 
3. Conservation: Environmental science advocates for the conservation of biodiversity, natural habitats, and ecosystem services to maintain ecological balance and promote long-term environmental health.
4. Pollution Prevention: Environmental science focuses on identifying sources of pollution, minimizing waste generation, and implementing strategies to prevent pollution and protect air, water, and soil quality.
5. Environmental Justice: Environmental science addresses environmental inequalities and advocates for equitable access to clean air, water, and land for all communities, regardless of socioeconomic status or geographic location.

C) Scope of Environmental Science:

1. Environmental Issues: Environmental science investigates a wide range of environmental issues, including climate change, deforestation, pollution, habitat loss, biodiversity loss, resource depletion, and waste management.

2. Sustainable Development: Environmental science plays a crucial role in promoting sustainable development practices that balance economic growth with environmental protection and social equity.

3. Conservation Biology: Environmental science includes the study of conservation biology, which focuses on preserving biodiversity, protecting endangered species, and restoring degraded ecosystems.

4. Environmental Policy: Environmental science informs environmental policy-making by providing scientific data and analysis to support evidence-based decision-making on environmental issues at local, national, and global levels.

5. Environmental Education: Environmental science contributes to environmental education initiatives that raise awareness about environmental issues, promote eco-friendly behaviour, and empower individuals to take action to protect the environment.

Components of Environment:

Atmosphere: The protective blanket of gases surrounding the earth: 

1. It sustains life on the earth, it saves it from the hostile environment of outer space, 
2. it absorbs most of the cosmic rays from outer space and a major portion of the electromagnetic radiation from the sun and
3. it transmits only here ultraviolet, visible, near infrared radiation (300 to 2500 nm) and radio waves. (0.14 to 40m) while filtering out tissue-damaging ultraviolet waves below about 300 nm.

The atmosphere is composed of nitrogen and oxygen. Besides, argon, carbon dioxide, and trace gases.

Hydrosphere: The Hydrosphere comprises all types of water resources oceans, seas, lakes, rivers, streams, reservoir, polar ice caps, glaciers, and groundwater. 

1. Nature 97% of the earth's water supply is in the oceans,
2. About 2% of the water resources is locked in the polar icecaps and glaciers.
3. Only about 1% is available as fresh surface water-rivers, lakes streams, and groundwater fit to be used for human consumption and other uses.

Lithosphere: The word lithosphere originated from a Greek word mean "rocky" + "sphere” i.e. the solid outmost shield of the rocky planet. The Earth is an oblate spheroid. It is composed of a number of different layers.

1. The Core which is around 7000 kilometres in diameter (3500 kilometres in radius) and is situated at the Earth's centre.
2. The Mantle which environs the core and has a thickness of 2900 kilometres.
3. The Crust floats on top of the mantle and is composed of basalt rich oceanic crust and granitic rich continental crust. 

Biosphere: Indicates the realm of living organisms and their interactions with environment, viz atmosphere, hydrosphere and lithosphere.

In summary, environmental science is a multidisciplinary field that addresses environmental challenges through scientific research, policy development, conservation efforts, and education to promote sustainable practices and safeguard the health of the planet and its inhabitants.