Origin of elements

Big Bang Theory

The theory that the universe originated from the explosion of an infinitely hot and dense ball of primordial matter, which initially formed hydrogen and helium; gravitational forces then collapsed gas clouds into galaxies and stars.

Fusion Reactions in Stars

The process by which elements heavier than hydrogen and helium are formed in the extremely high-temperature cores of stars; high temperatures overcome electrostatic repulsion between positively charged nuclei, allowing them to fuse.

Transuranium Elements

Artificially synthesized elements with atomic numbers beyond 92 (beyond uranium); produced in cyclotrons by accelerating high-energy particles to fuse with target nuclei; example: Californium.

Cyclotron

A particle accelerator used in the artificial/laboratory synthesis of transuranium elements; accelerates nuclei to high energies so they can fuse with target nuclei to create new elements.

Californium

A synthetic transuranium element formed by Glenn Seaborg using a cyclotron to accelerate C-12 nuclei to fuse with U-238; an example of laboratory/artificial synthesis of elements.

Elemental Composition of Earth

The earth’s crust is dominated by oxygen (48.86%), iron (18.84%), silicon (13.96%), and magnesium (12.42%); carbon makes up only about 0.10% of earth’s atoms.

CHONPS

The acronym for the six bulk elements found in organic compounds of the cell: Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, and Sulphur; these are the major building blocks of all biological molecules.

Bulk Elements (Biological)

Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, and Sulphur (CHONPS); the major elements found in the organic compounds of living cells, present in large amounts.

Trace Elements (Biological)

Elements found in small amounts in the fluids that bathe cells; include Na, K, Mg, Ca, B, V, Mn, Fe, Co, Ni, Cu, Zn, Si, Se, Cl, Br, and Cr; essential in small quantities for normal biological function.

Striking Features of Major Biological Elements

The major biological elements share these features: they are mostly p-block elements, they can form covalent bonds, they are non-metals, they have smaller atomic sizes/numbers, and they are neither too reactive nor inert.

Why Carbon Forms Many Compounds

Carbon is uniquely versatile because: (1) it has an ideal, intermediate atomic size enabling stable covalent bonds; (2) it is tetravalent (forms 4 bonds); (3) it has the power of catenation; (4) it can form single, double, and triple bonds with itself and other atoms.

Tetravalent (Carbon)

The property of carbon whereby it can form four covalent bonds simultaneously, allowing it to bond with four other atoms or groups and create a vast diversity of molecular structures.

Catenation

The ability of carbon atoms to bond with one another to form long chains, branched chains, and rings; gives rise to the enormous diversity of organic compounds.

Reasons Elements Were Excluded from Cells

Elements were not incorporated into cells due to: (1) their artificial nature (only synthetically produced), (2) their inert/unreactive nature, (3) their toxic nature, (4) their radioactivity.

Non-essential Elements with Medical Value

Some non-essential elements are medically useful: lithium compounds (Li₂CO₃) treat schizophrenia; platinum and gold complexes are used as anticancer and anti-arthritis preparations; kaolin (containing aluminum) has anti-diarrhoeal properties.

Life (Definition)

Life is a process capable of self-sustenance (replacing lost material), replication (continuity of species), and mutation (allowing progeny to adapt under natural selection in a changing environment).

Living Systems Theory

A theory proposing that living systems are open, self-organizing entities that interact with their environment, maintained by flows of information, energy, and matter; attempts to map general principles for how all living systems work.

Gaia Hypothesis

The hypothesis that organisms interact with their inorganic surroundings on Earth to form a synergistic, self-regulating complex system that maintains and perpetuates conditions for life; notes that atmospheric composition is remarkably stable despite thermodynamic disequilibrium.

Special Creation Theory

The view that life is so complex it required a supernatural force to generate it; held by Christian, Muslim, and African traditionalist worldviews; criticized by scientists because it cannot be empirically tested and does not obey natural laws.

Panspermia (Colonization) Theory

The theory that life originated elsewhere in the universe and was transported to Earth, possibly as living spores driven by light pressure from distant stars; proposed by Francis Crick and Leslie Orgel as directed panspermia; cannot be proven or disproven.

Directed Panspermia

The proposal by Francis Crick and Leslie Orgel that the transport of life to Earth from elsewhere in the universe was directed by intelligent forces; a variant of the panspermia (colonization) theory.

Spontaneous Generation Theory

The ancient theory that living organisms arise spontaneously from non-living matter; supported by Aristotle and Van Helmont; disproved by Francesco Redi and later by Pasteur; the discovery of the microscope by Anton van Leeuwenhoek enabled the study of microbial spontaneous generation.

Francesco Redi (1626–1697)

Italian scientist who dealt the first blow to the spontaneous generation theory by demonstrating that maggots did not arise spontaneously from meat when flies were prevented from laying eggs on it.

Anton van Leeuwenhoek

Dutch scientist who invented the microscope in 1675; his invention paved the way for studying the spontaneous generation of microbial life.

Haldane–Oparin Hypothesis (Long-term Spontaneous Generation)

The 20th-century proposal by J.B.S. Haldane (British Biochemist) and A.L. Oparin (Russian Biochemist) that life once evolved from non-living matter through chemical evolution on the primitive Earth; both developed the idea independently around 1920.

Chemical Evolution

The formation of complex organic molecules (monomers and macromolecules) from simple inorganic molecules on the primitive Earth; the first stage in the origin of life; raw materials came from the primitive reducing atmosphere.

Biological Evolution

The formation of a self-sustaining, self-replicating living system from the complex organic molecules produced during chemical evolution; the second major stage in the origin of life.

Primitive Atmosphere Composition

The primitive Earth’s atmosphere was reducing and contained: hydrogen (H₂), methane (CH₄), water vapour (H₂O), ammonia (NH₃), and probably hydrogen sulphide (H₂S); notably absent was free oxygen (O₂).

Reducing Atmosphere (Primitive Earth)

The primitive atmosphere was reducing because: there was little or no oxygen; Earth was formed mostly from hydrogen (a good reductant); meteors contained iron as Fe or Fe²⁺ and carbon as carbides or hydrocarbons; absence of O₂ meant no ozone layer to block UV radiation.

Miller–Urey Experiment (1950)

A landmark experiment by chemist Stanley Miller and physicist Harold Urey that simulated primitive Earth conditions by mixing CH₄, NH₃, H₂O, and H₂ (no O₂) and electrically sparking the mixture to simulate lightning; the result was the formation of amino acids (building blocks of proteins).

Prebiotic (Primordial) Soup Theory

The theory proposed independently by A.I. Oparin and J.B.S. Haldane that life began in an ocean or pond where chemicals from the primitive reducing atmosphere combined with energy sources to produce amino acids and other organic molecules that accumulated to form a rich “soup” approximately 3.8–3.55 billion years ago.

Haldane’s Soup (Primeval Soup)

The accumulation of biologically important organic compounds washed by rain into early oceans; persisted due to the absence of oxygen (which would have caused oxidative degradation); the concentrated prebiotic environment from which life is thought to have emerged.

Strecker Synthesis

A prebiotic pathway for the formation of amino acids in which an aldehyde reacts with HCN; steps: (1) ammonia reacts with aldehyde to form an imine; (2) cyanide adds to the imine forming an aminonitrile; (3) hydrolysis of aminonitrile gives the amino acid.

Formose Reaction

The prebiotic synthesis of monosaccharides (simple sugars) from formaldehyde; a series of aldol condensation reactions; proposed as a mechanism for forming sugars in the prebiotic environment.

Polymerization of HCN

The proposed prebiotic mechanism for the synthesis of nucleotide bases (purines and pyrimidines); HCN polymerizes under prebiotic conditions to form purine bases such as adenine and guanine.

Polymerization

The coming together of several monomers to form more complex macromolecules (polymers); through this process, polypeptides, polynucleotides, and polysaccharides could form in prebiotic conditions.

Condensation Reaction

A reaction in which two molecules join by removing water (H₂O); e.g., two glucose molecules forming a disaccharide; thermodynamically favoured when water is removed by evaporation or condensing agents.

Condensing Agents

Chemicals that promote condensation reactions (polymerization) by removing water; examples include carbodiimide, DAMN (diaminomaleonitrile), cyanamide, and polyphosphates like ATP; allowed polymerization in the prebiotic soup environment.

Probionts

The first primitive cell-like structures proposed by Oparin; formed when a membrane assembled around molecules with catalytic activity (most likely proteins); separated from surroundings and are considered precursors of true cells.

Coacervation

The spontaneous separation of an aqueous polymer solution into two phases — one with high polymer concentration (coacervate droplets) and one with low concentration; Oparin proposed this as the mechanism by which the first primitive cells (probionts) formed.

Coacervate Droplets

Polymer-rich droplets formed by coacervation; could interact with the aqueous environment to grow by acquiring additional compounds; some droplets could retain the catalyst-substrate properties of the parent, giving rise to progeny droplets; proposed by Oparin as primitive cell prototypes.

Fox’s Thermal Proteinoids

Micro-spheroidal aggregates formed when hot aqueous solutions of polypeptides cool; under suitable conditions they form microspheres several micrometers in diameter with a two-layer membrane similar to bacteria; could grow and bud; a proposed model for early protocells.

Naked Gene Hypothesis

The hypothesis that self-replicating macromolecules (nucleotides) could accumulate a shell of other substances in a manner similar to modern viruses; proposed as an alternative model for the origin of the first cells.

Ribozyme

An RNA molecule with catalytic (enzyme-like) activity; its discovery revolutionized thinking about the origin of life, suggesting that RNA can both store information and catalyze reactions; ribozymes are thought to have predated protein enzymes.

RNA World Hypothesis

The hypothesis that ribozymes (RNA enzymes) originated before translation systems and protein enzymes; after translation evolved, more efficient protein enzymes gradually replaced most ribozymes; supported by the discovery of ribozyme activity.

Protein vs. Nucleic Acid (Evolutionary Priority)

Proteins have structural and catalytic functions while nucleic acids carry genetic information; the most plausible view is that proteins and nucleic acids evolved in parallel, with polynucleotides specifying polypeptides (translation) and polypeptides catalyzing nucleotide replication.

Development of Metabolic Pathways

As nutrients in the prebiotic soup became scarce, organisms developed enzymatic systems (metabolic pathways) to synthesize monomers from simpler precursors; this drove the evolution of increasingly complex biochemistry including energy-producing pathways.

Evolution of Photosynthesis

As prebiotic energy-rich compounds became scarce, photosynthesis evolved to harness sunlight; initially H₂S was the reductant; when H₂S was exhausted, the system evolved to use water (H₂O) as the reductant, producing O₂ as a byproduct.

Role of Oxygen in Evolution

The accumulation of O₂ from water-splitting photosynthesis was initially toxic to early organisms; organisms evolved aerobic respiration to use O₂ as an efficient oxidizing agent; the resulting ozone (O₃) layer then shielded Earth from UV radiation, enabling new forms of life.

Formation of the Ozone Layer

The ozone layer formed only after photosynthetic organisms produced sufficient atmospheric O₂ from the oxidation of water; it was absent on the primitive Earth (explaining why prebiotic molecules could form under UV radiation); now shields life from harmful UV rays.