|A depiction of a spark, in an electric discharge device, of the Miller-Urey experiment variety.|
A number of people assert that 28 Jun 1914 shooting of Austro-Hungarian Archduke Franz Ferdinand by the Bosnian Serb student Gavrilo Princip, a member of the Serbian terrorist organization Black Hand, was the "spark" led to the tipping point, that, within thirty days, led to a global chain reaction that led to WWI, claiming ten million lives, and followup WWII, claiming another thirty million. 
The following are related quotes:
“The affinity basically indicates, what people normally call ‘chemistry’ or the ‘spark’. This chemistry pretty much depends on the compatibility, like having similar likes, similar hobbies, similar ways of thinking, the more affinity the lowest energy and therefore more stability. It sounds tricky, but it is a fundamental principle. Sometimes we think love can manage everything, which for some exceptional cases it can, but there must be affinity in order to be stable.”— Andres Florez (2013), “Thermodynamics of Love”, Mar 19 
“Why is defining life so frustratingly difficult? Why have scientists and philosophers failed for centuries to find a specific physical property or set of properties that clearly separates the living from the inanimate? Because such a property does not exist. Life is a concept that we invented. On the most fundamental level, all matter that exists is an arrangement of atoms and their constituent particles. These arrangements fall onto an immense spectrum of complexity, from a single hydrogen atom to something as intricate as a brain. In trying to define life, we have drawn a line at an arbitrary level of complexity and declared that everything above that border is alive and everything below it is not. In truth, this division does not exist outside the mind. There is no threshold at which a collection of atoms suddenly becomes alive, no categorical distinction between the living and inanimate, no Frankensteinian spark. We have failed to define life because there was never anything to define in the first place.”— Ferris Jabr (2013), “Why Life Does Not Really Exist”, Dec 2 
● Spark of life theory
● Spark of the tongue
1. (a) Buchanan, Mark. (2000). Ubiquity: Why Catastrophes Happen (pg. 3; spark, 2+ pgs). Three Rivers Press.
(b) Doak, Robin S. (2009). Assassination at Sarajevo: The Spark That Started World War I. Capstone.
2. (a) Florez, Andres. (2013). “Thermodynamics of Love”, Science & Salsa, Blogspot.de, Mar 19.
(b) Florez, Andres. (2014). “Thermodynamics of Love”, Insanitek.net, Feb 3.
3. Jabr, Ferris. (2013). “Why Life Does Not Really Exist”, Scientific American, Brainwaves Blog, Dec 2.