Earliest Eon Or Lowest Eonothem
The full name of the earliest possible geochronologic eon or lowest chrono-stratigraphic eonothem or the informal name ("Precambrian") attributable to the stratigraphic horizon from which the cataloged item was collected.
`Phanerozoic`, `Proterozoic`
http://rs.tdwg.org/dwc/terms/
Geological Context
Geological Context