Origin and Evolution of Life

Flashcards covering the origins of life, chemical evolution steps, major scientific experiments (Urey-Miller), RNA World hypothesis, Darwin's postulates of evolution, and Mutation Theory.

Protobiogenesis

The technical term for the origin of life.

Theory of special creation

The oldest theory of the origin of life, based on religious belief, stating all living organisms were created by a super-natural power.

Cosmozoic theory (Theory of Panspermia)

A theory suggesting life originated on other planets and descended to Earth as spores or micro-organisms called cosmozoa or panspermia.

Theory of spontaneous generation (Abiogenesis)

The theory that life originated from non-living (inanimate) material spontaneously; it was later disproved by Louis Pasteur.

Theory of biogenesis

The theory that living organisms are always produced from pre-existing living forms through reproduction.

Chemical Evolution of Life (Self assembly theory)

The theory developed by Oparin ($1924$) and Haldane ($1929$) stating life originated on Earth through combinations of chemicals over a long period.

Big-Bang theory

Proposed by Georges Lemaitre ($1931$), it explains that the Universe originated about $20$ billion years ago from a single huge titanic explosion.

Nebula

A rotating cloud of hot gases and cosmic dust from which the Earth originated approximately $4.6$ billion years ago.

Reducing atmosphere

The primitive atmosphere of Earth which was devoid of free oxygen and rich in hydrogen, carbon, nitrogen, and sulphur.

Hot dilute soup (Primitive broth)

A term used by Haldane to describe the accumulation of simple organic molecules at the bottom of water bodies that showed no degradation due to the absence of oxygen and enzymes.

Protoproteins

Molecules formed by the polymerisation of amino acids which later formed proteins, considered a landmark in the origin of life.

Protobionts

Prebiotic chemical aggregates having some properties of living systems, formed from nucleic acids along with organic and inorganic molecules.

Coacervates

Colloidal aggregations of hydrophobic proteins and lipids, a term coined by Oparin ($1924$).

Microspheres

Stable protenoids formed from colloidal hydrophilic complexes surrounded by water molecules, described by Sidney Fox.

Eobionts (Protocell)

The first primitive living systems that evolved from colloidal aggregations of coacervates or microspheres.

Spark-discharge apparatus

The glass apparatus used in Urey and Miller's experiment to provide physical evidence for the chemical evolution of life.

Urey and Miller Gas Ratio

The specific proportion of methane, ammonia, and hydrogen ($1:2:2$) pumped into the glass chamber during their experiment.

Ribozymes

Catalytic RNA molecules that act as biocatalysts, discovered by Sidney Altman and Thomas Cech.

RNA World Hypothesis

The hypothesis suggesting that early life was based exclusively on nucleic acids, most probably RNA; proposed by Woese, Crick, and Orgel in $1960$.

Organic evolution

Slow, gradual, continuous, and irreversible changes through which present-day complex life forms developed from simple pre-existing forms.

Theory of continuity of Germplasm

A theory proposed by August Weismann stating that variations in germ cells ($\text{germplasm}$) are inherited, while variations in somatic cells are not.

Prodigality of nature

Darwin's first postulate; the natural tendency of living things to produce a large number of progeny in a geometric ratio.

Natural Selection

The principle by which useful variations are preserved by nature; Herbert Spencer referred to this process as 'survival of fittest'.

Speciation

The process by which favorable variations are transmitted and fixed over generations, eventually giving rise to a new species.

Mutation Theory

Proposed by Hugo de Vries ($1901$) using the plant Oenothera Lamarckiana, stating that evolution occurs through sudden, random, and heritable variations.