Missed Connections in the Archean.

Greetings. Alien visitation. The possibility is fascinating to ponder, challenging to consider, and easily considered from a biased, homocentric point of view. 

The Archean Eon is the second of the four geologic eons of Earth's long and storied history, preceded by the Hadean Eon and followed by the Proterozoic. The Archean represents the time period from approximately 4,031 to 2,500 million years ago. The Late Heavy Bombardment is hypothesized to have overlapped with the earliest stages of the Archean. The Huronian glaciation occurred at the very end of the Archean Eon. 

The Earth during the Archean was mostly a water world, the planet possessing a continental crust, but with the majority submerged underneath a global ocean substantially deeper than today's oceans. Except for some rare relict crystals, today's oldest continental crust dates back to the Archean, however, much of the geological detail of the Archean has been destroyed by subsequent tectonic and environmental activity. The Earth's atmosphere was also vastly different in composition from today's, the prebiotic atmosphere being a reducing atmosphere rich in methane gas and lacking any free oxygen. 

The earliest known life, mostly represented by shallow-water microbial mats known as stromatolites, first emerged during the Archean and remained simple prokaryotes (archaea and bacteria) throughout the entirety of the eon. The earliest photosynthetic processes, especially those by early cyanobacteria, appeared by the middle of the Archean and eventually led to a permanent chemical change in the composition of the world's oceans and the surrounding atmosphere after the Archean. 

It goes without saying that if alien visitation occurred in the distant past, say the Archean, then those extraterrestrial explorers would not have come across any intelligent life to examine, much less anything else of any appreciable complexity. When considering the possibility of alien visitation, the UFO subculture comes at the problem from an extremely homocentric approach, only considering the possibility of alien visitation in historical times, completely missing the extraterrestrial boat as it were. The Earth is over four and a half billion years old. That singular fact leaves a humongous amount of time for extraterrestrials to happen upon the planet, with the vast majority of the planet's long history completely void of complex life forms. 

Extraterrestrials, if they were able to make the tremendously long and arduous journey through interstellar space, would most likely have arrived during periods when the planet was devoid of intelligent life; the Carboniferous, the Permian, or the Ordovician. The chances that aliens would arrive during times when the biosphere hosted intelligent creatures is depressingly low, with all time periods from the Triassic onward accounting for only a small percentage of the total time that life has existed on the planet. Aliens might have come across a somewhat barren rocky planet, completely devoid of complex life forms, a situation which may have motivated them to not make a return journey. 

Homo sapiens has only been in existence on the Earth for an extremely short period of time, at least in geologic terms. The vast majority of the long history of the Earth is vacant of our unimportant species. We are not special, and we should critically think in those terms. Something to consider. 

Thank you for your time and consideration.