Editing Hadean Eon (section)

=== '''Etymology''' ===
The eon's name comes from '''[[Hades]]''', [[Greek Religion|<u>Greek</u> god]] of the <u>Underworld</u>; it is a poetic reference to the extreme environmental conditions of early <u>Earth</u>.

Other names: Priscoan Period (from ''priscus'', 'ancient'); pre-Archean (deprecated)

'''Eons''' are the longest portions of geologic time ('''eras''' are the second-longest). Three eons are <u>formally</u> recognized: the [[Phanerozoic Eon]] (dating from modern times back to the beginning of the <u>Cambrian Period</u>), the [[Proterozoic Eon]], and the [[Archean Eon]] - the '''Hadean Eon''' is an <u>informal</u> predecessor.  

==== Informal? ====
The eon is characterized by an almost complete absence of preserved rock formations. The oldest known rocks on <u>Earth</u> date back to about 4.0 billion years ago, towards the end of the Hadean. Without significant rock records, it's challenging for geologists to define and study this eon using traditional geological techniques. Geological time scales are primarily based on significant events in <u>Earth's</u> history, often marked by changes in the rock record, such as mass extinctions or major shifts in life forms, sedimentation, or atmospheric composition. The Hadean lacks these clear markers in the rock record, making it harder to define using the criteria applied to later geological periods.