The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.
N = R* • fp • ne • fl • fi • fc • L
- R* = the average rate of star formation in our Milky Way galaxy.
- fp = the fraction of those stars that have planets.
- ne = the average number of planets that can potentially support life per star that has planets.
- fl = the fraction of planets that could support life that actually develop life at some point.
- fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations).
- fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
- L = the length of time for which such civilizations release detectable signals into space.
The Drake Equation is effectively a box of conjectures shaken periodically to produce a new estimate of the likelihood of finding exo-intelligent life. It’s like an utterly fanciful Bayesian attempt at predicting the unpredictable. Take one sample, Earth, and from it, and our observable views and knowledge of space, derive a probability that humanity will find intelligent life outside of our solar system.
There’s nothing really scientific about it even though it tries to use some basis to remain accurate. If an accurate conjecture is even a real thing… But that’s why it’s so alluring. ANYONE can play with Drake’s Equation and come up with a number that means something to them. And your number will be just as ‘right’ as anyone else’s!
With this in mind I now present a list of somewhat appropriate concepts that may or may not influence one or more of the Drake Equation parameters. In a generally descending order of importance:
- Liquid water.
- Goldilocks location.
- A heliosphere.
- Distance from the galactic center,
(outside most bursts of intense radiation – gamma rays, and avoidance of intense space weather which may affect agriculture).
- A molten iron core planet producing a planet protecting magnetosphere.
- The existence of asteroid and comet belts (Kuiper Belt, Oort Cloud) which would both deliver supplemental elements as well as disrupt stagnant evolution.
- Volcanism, plate tectonics and the recycling of minerals and elements through volcanism, continental ridges
(CO2, sulfur, calcium, all need to be recycled).
- Earth tilt. Seasons contributed to the stress need to spur life into intelligence.
- The Moon. A moon of sufficient size and limited distance to stabilize the tilt of Earth’s axis and to adsorb some portion of the asteroid/comet impacts.
- Continental configuration. Island states would not produce intelligent life. Milankovitch cycles, the northern hemisphere’s influence on heating and cooling cycles.
- Oceans filtered toxin free by biotic life over 3.5 billion years and the generation of oxygen by this life.
- The generation of ozone, or its equivalent, that shields DNA from constant mutation.
- Biotic life had an impact on the evolution of the Earth’s crust and hence an influence on higher life forms.
- Star death required to produce higher atomic weight elements necessary for life processes. Universally young stars could not have harbored life on their planets due to low molecular weight of elements.
- Although our solar system is in the process of emerging from the Local Bubble, the sun’s trajectory suggests that it will probably not encounter a large, dense cloud for at least several more million years. The consequences of such an encounter for the earth’s climate are unclear; however, one wonders whether it is a coincidence that Homo sapiens appeared while the sun was traversing a region of space virtually devoid of interstellar matter.
- Disease. Humanity, and higher forms of life in general, must have survived disease. Disease has killed more human life than all the wars, religions and genocides put together.
- Strong presence of nuclear reactive materials in Earth crust that may have contributed to the spawning of life.
- 3.5 billion years of hydrocarbon concentration perfectly delivered at just the right time to drive humanity over the population threshold that sparked the industrial revolution.
- The expedient use and transition from fossil fuels to non-environmental impacting technologies (to avoid calamitous climate change.)
- Miscellaneous items of lesser importance:
- Metal: easy access to metals of many types must be available for advanced alien life (industry, electronics, astro-exploration).
- Guano: bird droppings strangely enough has made an enormous impact on the development of humanity.
- Rubber: The existence of a rubber tree and the textile extracted from it also had an immense impact on the development of humanity.
Random points supporting the theory that life is unique:
- Change. Change is probably one of the primary drivers of higher life forms. Many of the above points that would influence the evolution of life on a planet are change based. Without change, often drastic change (chemical, climate, temperature, radiative, water currents, minor planet tilt aberrations) life would get ‘stuck’ in static ecological configurations. Externally induced change spurs evolution.
But too much change would also be detrimental to the evolution of intelligent life. Change must be of just the right amount, just enough asteroid impacts, just enough volcanism, just enough galactic radiation, just enough coronal mass ejection, just enough planetary tilt, just enough continental drift and distribution. Just enough to provoke limited change but not too much to continuously be wiping the evolutionary slate clean.
- Earth has been emitting life signs spectroscopically for 3.5 billion years. If alien intelligences had been looking, they would have found this planet by now.