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What is Life? Definition, Life’s Origin and Forms

tree of ife
Dashamlav | 9 September 2020 (अंतिम बदलाव: 10 November 2020)

Life is the property of a physical entity that enables it to perform biological functions such as homeostasis, metabolism and reproduction. Physical entities which poses life are called organisms or living beings. Life also separates living beings from non-living (entities that never have had life) and dead (entities wherein biological functions have stopped). Biology is the branch of science which studies organisms and their functioning.

Life bestows the living organisms with abilities like movement, growth, response to stimuli, adaptation among many others. We do not know how life came into existence for the first time on Earth.  So far, we also do not know what exactly is responsible for giving life and its functions to an organisms. There are several theories in this regard, most of them agree that consciousness is what distinguishes living from non-living things. However, the nature of consciousness is not yet known.

Definition of Life: the condition that distinguishes animals and plants from inorganic matter, including the capacity for growth, reproduction, functional activity, and continual change preceding death.

Definition of Life as per Physics: Thermodynamically, life is an open system which makes use of gradients in its surroundings to create imperfect copies of itself.

Philosophical Definition of Life: Life is the aspect of existence that processes, acts, reacts, evaluates, and evolves through growth.

Functions of Life

Living beings can perform a large number of biological functions that non-living can not. Some of these functions are described below.

1. Reproduction

A living organism is able to make new individual organisms through the biological process of reproduction. It’s almost like making copies of itself. Reproduction can be asexual (one parent is capable of producing new individual) or sexual (two parents participate in producing new individual). Reproduction is necessary for the propagation of life and its forms.

2. Metabolism

Living organisms need energy to live and perform any of the functions. Organisms have the ability to convert chemical elements into organic compounds and decomposing them back into simpler matter and energy. Thus organisms acquire energy from their surroundings and live through their lifespan.

3. Homeostasis

Homeostasis means that the living organisms can adjust their internal environment to attain a constant and stable state. For example, when body temperature rises,  many organisms sweat in order to bring the temperature down to the optimum level.

4. Adaptation

A living organism posses the ability to adapt itself according to its external environment. Those organisms which fail to adapt; their species perishes with time. Adaptation is fundamental to the process of evolution of life. Through evolution, life forms becomes more complex, more resilient and more intelligent.

5. Organization

Cell is the basic unit of life. A cell is the smallest physical entity with life. As life forms evolved, multicellular organisms came about. In such organisms, a large number of cells organize together and act as a single living entity.

6. Growth

Living organisms grow during their lifespan. They grow in size, complexity and they also demonstrate growth in their ability to perform more functions.

tree of ife: origin and evolution of major life forms

Where Does the Life Exists?

The planet Earth is brimming with millions of life forms. From very small to very big; simple to very complex; ancient to relatively new — Earth has all sorts of living organisms. However, Earth is the only place where life has, so far been, found. It is true that we have only scantily explored a minuscule part of our solar system. The universe is unimaginably huge — it contains trillions of stars with innumerable planets. Therefore, the probability of the existence of extraterrestrial life can never be insignificant. We do not know if we will ever be able to find extraterrestrial life, let alone intelligent life, so we must protect our planet and this phenomenally phenomenon called the life.

How did Life Originate on Earth?

Earth was formed about 4.5 billion years ago. For a long time, the planet was too hot for life to rise. It is estimated that life has been there on Earth for at least about 3.5 billion years. Scientists believe that life began on Earth through abiogenesis; i.e. creation of life from non-living matter like organic compounds. Then over these billions of years, life evolved as it took millions of increasingly more advanced forms. It is estimated that 99% of all the species that ever lived on Earth are now extinct. We find some information about some of those extinct life forms only from their fossils.

Initially the life started in Earth’s oceans. The Tiktaalik fossils discovered in northern Canada, gives us information on how organisms living in the oceans adapted and moved out on land.

Some researchers also believe that the organic compounds necessary for life’s initiation came to the Earth when on an asteroid which had struck the planet.

Oldest Life on Earth

In December 2017, a report mentioned that some 3.46 billion years old rocks found in Australia used to harbor microorganisms. This is the oldest direct evidence of life on Earth.

  • Dinosaurs evolved about 240 million years ago
  • Mammals came into existence about 200 million years ago
  • Flowers originated 180 million years ago
  • Modern humans (Homo sapiens) came into existence about 0.2 million (200,000) years ago in the African continent.

ALSO SEE: Life Expectancy and Average Human Lifespan

Forms of Life

Life exists in millions of forms on Earth. There is so much variety in life forms that it becomes difficult to find words to appreciate the nature’s skills. We have unicellular life forms like bacteria and then we have highly advanced multicellular life forms like mammals. There are immobile, autotrophic lives like plants and there are also heterotrophic life forms like animals. From microscopic bacterium to massive whales, life exists in all shapes and sizes.

There is no agreement on whether virus should be considered living or non-living. Virus is one of the most fascinating thing — it, in fact, strengthens the argument that life could indeed originate from non-living matter. A virus is capable of replication but it does not have any other biological functions that we normally associate with life. Thus virus is considered to be the connecting link between living and non-living.

Probably the most advanced form of life on Earth is Homo sapiens — the human beings. We have arrived at our present stage through evolution of life happened over billions of years. Through humans, life exhibits some of its most extraordinary properties which are not present in any other known organism. Humans are capable of critical thinking, making art, music, machines among other capabilities.

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