Obsolete Scientific Theories

Biology
• Spontaneous generation. Falsified by an experiment by Louis Pasteur.
• Transmutation of species, Lamarckism, inheritance of acquired characteristics. Spontaneous generation of complex life from inanimate matter. Rendered obsolete by Darwinian evolution and Mendelian genetics.
• Maternal impression. The theory that the mother's thoughts created birth defects. Rendered obsolete by genetic theory.
• Miasma theory of disease.  The theory that diseases are caused by "bad air". Rendered obsolete by the germ theory of disease (1880's).
• Preformationism – The theory that all organisms have existed since the beginning of life, and that gametes contain a miniature but complete preformed individual, in the case of humans, a homunculus. Rendered obsolete by cytology, discovery of DNA, and atomic theory.
• Telegony – the theory that an offspring can inherit characteristics from a previous mate of its mother's as well as its actual parents. The idea of telegony goes back to Aristotle. It states that individuals can inherit traits not only from their fathers, but also from other males previously known to their mothers. in other words, fatherhood is not indivisible: paternity can be partitioned. Past association to racism.
• Vitalism – the theory that living things are alive because of some "vital force" independent of nonliving matter. It was gradually discredited by the rise of organic chemistry, biochemistry, and molecular biology, fields that failed to discover any "vital force". Friedrich Wöhler's synthesis of urea from ammonium cyanate was only one step in a long road, not a great refutation.
• Azoic hypothesis (1843) - that marine life cannot exist below 300 fathoms. Disproven in 1850 with the discovery of Rhizocrinus lofotensis (450 fathoms).  In 1869, Charles Wyville Thomson dredged marine life from a depth of 2,345 fathoms (14,070 ft).

Chemistry
• Caloric theory (1770s) – that heat consists of a self-repellent fluid called 'caloric' that flows from hotter bodies to colder bodies. Lavoisier's successor to phlogiston (Antoine Lavoisier was one of the first to use a calorimeter to measure the heat changes during chemical reaction). Caloric was also thought of as a weightless gas that could pass in and out of pores in solids and liquids. Caloric theory was discredited by Rumford's and Joule's work.
• Classical elements - All matter was once thought to be composed of various combinations of classical elements (eg, air, earth, fire, and water). This was finally refuted by Lavoisier's publication of Elements of Chemistry, which contained the first modern list of chemical elements (1789).
• Phlogiston theory (1667) – The theory that combustible goods contain a substance called "phlogiston" which entered air upon combustion. Replaced by Lavoisier's work on oxidation (1778).
• Point 2 of Dalton's Atomic Theory was obsoleted by discovery of isotopes; point 3 by discovery of subatomic particles and nuclear reactions.\

Physics
• Emission theory of vision – the proposal that visual perception is accomplished by rays of light emitted by the eyes. Replaced by intromission theory.
• Aristotelian physics – superseded by Newtonian physics.
• Ptolemy's law of refraction - replaced by Snell's law.
• Luminiferous aether – postulated medium for the propagation of light. Failed to be detected by the sufficiently sensitive Michelson-Morley experiment (1887). Made obsolete by Einstein's work.
• Caloric theory – that heat consists of a self-repellent fluid called 'caloric' that flows from hotter bodies tocolder bodies. Lavoisier's successor to phlogiston (Lavoisier was one of the first to use a calorimeter to measure the heat changes during chemical reaction). Caloric was also thought of as a weightless gas that could pass in and out of pores in solids and liquids. Caloric theory was discredited by Rumford's and Joule's work.
• Contact tension – an erroneous scientific theory from the Enlightenment that attempted to account for all the sources of electric charge known at the time. It has been superseded by more modern notions.
• Vis viva – From the Latin for "Living Force". Gottfried Leibniz's elementary and limited early formulation of the principle of conservation of energy.  Now known as kinetic energy.
• Emitter theory – also called emission theory or ballistic theory of light, was a competing theory for the special theory of relativity attempting to explain the results of the Michelson–Morley experiment of 1887. Emission theories obey the principle of relativity by having no preferred frame for light transmission, but say that light is emitted at speed "c" relative to its source instead of applying the invariance postulate. This light propogation theory is discredited by most scientists.
• Balance of nature – a theory that proposes that ecological systems are usually in a stable equilibrium or homeostasis with the implication that small changes in a particular parameter (eg, the size of a particular population) will be corrected by some negative feedback that will bring the parameter back to its original "point of  balance" with the rest of the system.  The Gaia hypothesis (James Lovelock) is a balance of nature-based theory that suggests that the Earth and its ecology may act as co-ordinated systems in order to maintain the balance of nature. A powerful argument against the Gaia hypothesis is the assertion (such as that made by Richard Dawkins in ‘The Extended Phenotype’) that Gaia cannot arise from Darwinian evolution of life — the planet as a whole is not a unit of selection. The theory that nature is permanently in balance has been largely discredited, as it has been found that chaotic changes in population levels are common, but nevertheless the idea continues to be popular. During the latter half of the twentieth century the theory was superseded by catastrophe theory and chaos theory.   
• Progression of atomic theory:
 i) Democritus, the originator of atomic theory, held that everything is composed of atoms, which are indestructible.
 ii) John Dalton's model (1803): that atoms are indivisible and indestructible (superseded by nuclear physics) and that all atoms of a given element are identical in mass (superseded by discovery of atomic isotopes).
 iii) J.J. Thompsom's 'Plum Pudding' model (1904): that protons and electrons were mixed together in a single mass.
 iv) Rutherford  model (1911): atom with an impenetrable 'nucleus' orbited by electrons.
 v) Bohr model (1913): depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus — similar in structure to the Solar System, but with attraction provided by electrostatic forces rather than gravity. Electrons behave with quantized orbits.
vi) Electron Cloud model (1926). Current theoretical model of the atom that portrays a probabilistic "cloud" of electrons surrounding the nucleus. Developed by Erwin Schrödinger and Werner Heisenberg using quantum mechanics.  The electron cloud model assigns electrons to different atomic orbitals which are all not spheres. The atomic orbitals give explanation on the patterns within the periodic table.
 vii) All of classical physics, including Newtonian physics is superseded by relativistic physics and quantum physics. Classical physics is a limiting case of the latter two theories which it is often a very good approximation.

Astronomy and Cosmology
• Ptolemaic system (~150AD) – geocentric cosmology in which the Earth is stationary and at the center of the universe. Replaced by Heliocentric model.
• Copernican Heliocentric universe (1543) – astronomical model developed Nicolaus Copernicus in which the Earth and planets revolve around the Sun at the center of the Solar System. Made obsolete by discovery of the structure of the Milky Way. Heliocentrism only applies to the Solar System, and only approximately, since the Sun's center is not at the Solar System's center of mass.
• Newtonian gravity (1687) – Newton's law of universal gravitation states that a particle attracts every other particle in the universe using a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.  Superseded by general relativity, to which it is an excellent approximation unless speeds approach that of light. The anomalous perihelion precession of Mercury was the first observational evidence that Newtonian gravity was not totally accurate.
• Luminiferous aether theory - the postulated medium for the propagation of light (late 19th century). If light is a wave, it needs a medium to travel through, just like sound waves, or water waves, or string vibrations.   It was a very sound premise. Over time, cosmologist observed that the mechanical qualities of the aether had become more and more magical: it had to be a fluid in order to fill space, but one that was millions of times more rigid than steel in order to support the high frequencies of light waves. It also had to be massless and without viscosity, otherwise it would visibly affect the orbits of planets. Additionally it appeared it had to be completely transparent, non-dispersive, incompressible, and continuous at a very small scale. The Michelson-Morley experiment of 1887 failed to find an Aether. Later, the Theory of Relativity (1905, 1916) explained why the experiment failed to see aether and suggested that aether wasn't needed.
• Steady State Theory (1948) - postulates that the density of matter in the expanding universe remains unchanged due to a continuous creation of matter; that the expanding universe was in a steady state and had no beginning. It was a competitor of the Big Bang model. It is now rejected by the vast majority of cosmologists, astrophysicists and astronomers, as the observational evidence points to a hot Big Bang cosmology with a finite age of the universe. In 1964, the cosmic microwave background radiation was discovered, which was crucial evidence in favor of the Big Bang model.
• Hypothetical Planets: Counter-Earth (planet on the other side of the sun from that of the Earth); 5th Planet (planet between Mars & Jupiter); Planet 9 (attempts to explain the improbable orbital configuration of a group of trans-Neptunian objects-beyond the Kuiper belt; the first trans-Neptunian object to be discovered was Pluto in 1930.); Theia (a Mars-sized impactor believed to have collided with the Earth approximately 4.5 billion years ago-an event that created the Moon; the lunar rock samples retrieved by Apollo astronauts were found to be very similar in composition to Earth's crust); Vulcan (believed to existed inside the orbit of Mercury; the perturbations in Mercury's orbit were later accounted for via Einstein's General Theory of Relativity); Tyche (a hypothetical planet in the Oort Cloud supposedly responsible for producing the statistical excess in long period comets in a band. Results from the WISE telescope survey in 2014 have ruled it out).

Geography and Climate

• Flat Earth theory - a conception of the Earth's shape as a plane or disk.
• Terra Australis - Latin for "south land". The existence of Terra Australis was not based on any survey or direct observation, but rather on the idea that continental land in the Northern Hemisphere should be balanced by land in the south.
• Hollow Earth theory - proposes that the planet Earth either is entirely hollow or otherwise contains a substantial interior space.
• The Open Polar Sea - an ice-free sea once supposed to surround the North Pole.
• Rain Follows the Plow – the basic premise was that human habitation and agriculture through homesteading effected a permanent change in the climate of arid and semi-arid regions, making these regions more humid. The theory was widely promoted in the 1870s as a justification for the settlement of the Great Plains of the North America, a region previously known as the "Great American Desert".
• Island of California – refers to a long-held Spanish misconception, dating from the 16th century, that California was not part of mainland North America but rather a large island separated from the continent by a strait now known as the Gulf of California.

Geology
• Abiogenic petroleum origin - a hypotheses which proposes that petroleum and natural gas are formed by inorganic means rather than by the decomposition of organisms.
• Catastrophism - theory that the Earth has been affected in the past by sudden, short-lived, violent events. Largely replaced by Uniformitarianism in which slow incremental changes, such as erosion, created all the Earth's geological features.
• Flood geology - attempt to interpret and reconcile geological features of the Earth in accordance with a literal belief in the global flood described in Genesis 6–8. Replaced by modern geology and stratigraphy.
• Neptunism (1787) - the theory that rocks formed from the crystallization of minerals in the early Earth's oceans. Replaced by Plutonism - the geologic theory that the igneous rocks forming the Earth originated from intrusive magmatic activity, with a continuing gradual process of weathering and erosion wearing away rocks, which were then deposited on the sea bed, re-formed into layers of sedimentary rock by heat and pressure, and raised again.
• Expanding Earth theory -  hypothesis asserts that the position and relative movement of continents is at least partially due to the volume of Earth increasing. Replaced by Plate Tectonics theory in that the Earth's outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core.
• Geosyncline theory - a geosyncline was described as a subsiding linear trough that was caused by the accumulation of sedimentary rock strata deposited in a basin and subsequently compressed, deformed, and uplifted into a mountain range, with attendant volcanism and Plutonism. Replaced by Plate Tectonics.
• Continental Drift (1596) - the idea of continental drift has been subsumed by the theory of plate tectonics, which explains how the continents move.

Medicine
• Theory of the Four Bodily Humours - Humorism was a system of medicine detailing the makeup and workings of the human body, adopted by Ancient Greek and Roman physicians and philosophers, positing that an excess or deficiency of any of four distinct bodily fluids in a person directly influences their temperament and health. The four humors of Hippocratic medicine are black bile ('melancholic' - analytical, wise, and quiet), yellow bile ('choleric' - short-tempered, fast, or irritable), phlegm ('phlegmatic' - relaxed and peaceful), and blood ('sanguine' - enthusiastic, active, and social) and each corresponds to one of the traditional four temperaments.
• Eclectic Medicine – branch of American medicine which made use of botanical remedies and physical therapy practices; popular in the latter half of the 19th and first half of the 20th centuries. Transformed into alternative medicine and is no longer considered a scientific theory.
• Physiognomy -  the assessment of character or personality from a person's outer appearance, especially the face. Related to phrenology-a pseudomedicine which took the position that the brain is the organ of the mind, and, using measurements of the human skull, that certain brain areas have localized, specific functions or modules.