Once upon a time, scientists actually believed the world was flat, the center of the universe, and composed of four elements. These were not views held by crackpot theorists living on the fringes of society – reputable scholars representing the scientific community held these beliefs. That is, until radical thinkers brought to light new evidence to cause paradigm shifts that would evolve our understanding of the world we inhabit.
Here are five other obsolete theories once commonly accepted by mainstream science.
1. Emission Theory
No, this isn’t some theory of comedy. Humorism was a system of medicine that held that human health was controlled by the balance of four bodily fluids known as the “four humors” – blood, phlegm, yellow bile, and black bile. Ancient Greek and Roman physicians thought that having too much or too little of any of these fluids would negatively influence your well-being, and this theory was widely accepted in Western medicine until the nineteenth century – a span of over 2,000 years.
Remember the “medical” practice of bloodletting through cutting or the application of leeches? That was due to a belief that the body had too much blood relative to the other humors. If you were believed to have too much phlegm, your treatment was much more enjoyable: you may be served wine, a food associated with yellow bile, which counterbalances phlegm.
The theory of the four humors is closely associated with the classical elements, and in fact, each humor has an associated element: blood/air, phlegm/water, black bile/earth, and yellow bile/fire. This internal consistency no doubt lent the theory greater credibility.
4. Expanding Earth Theory
When it was discovered that South America fit so snugly into the nook of Africa, scientists puzzled over hypotheses that could explain the apparent continental drift. As of the 1970s, the prevailing theory is plate tectonics, but one popular theory before that was that the Earth was expanding, increasing in volume like a balloon being inflated.
While the notion may sound ridiculous to us today, it was first put forth by none other than Charles Darwin after observing raised beaches in Patagonia. It seemed to him that a huge area of South America had been raised upward, and he hypothesized that this was caused by the gradual expansion of the Earth. Since then, measurements and models have largely debunked any idea that our planet is growing in size, and the theory of plate tectonics offers better solutions to the puzzles that the expanding Earth theory was attempting to resolve.
A big problem that the expanding Earth theory faced was a plausible mechanism for the expansion – why would the Earth be growing? A modern supporter of an expanding Earth theory, interdisciplinary scientist J. Marvin Herndon believes that the Earth formed from a Jupiter-like planet that lost its gaseous atmosphere in a sudden and catastrophic event. The gas would have previously been exerting pressure on the planet, squeezing it, and with the gas removed, the Earth would then expand like a giant stress ball released from a tight grip.