Emergentearth: Written in the Rocks
"Geological epochs are one of the definable units that geologists and paleontologists use to break down the broad concept of deep time. These units of time are defined by stratigraphic layers that are chemically or biologically distinct. Epochs are defined on a global level, and their beginning and end are dated to specific points in time. Hominins first appear by around 6 mya, in the Miocene epoch, which ended about 5.3 mya. Our evolutionary path takes us through the Pliocene, the Pleistocene, and finally into the Holocene, starting around 12,000 years ago. The Anthropocene would follow the Holocene" (human origins.si.edu - The Smithsonian Institution)
stratigraphy: "the science of the layering of strata and its content, in radiogenic and stable isotopes chronology, and in age and duration calculations using orbital tuning models" (The Geologic Time Scale, 2012, p. xv); "from Latin stratum + Greek graphia, is the description of all rock bodies forming the Earth's crust and their organization into distinctive, useful, mappable units based on their inherent properties or attributes in
order to establish their distribution and relationship in space and their succession in time, and to interpret geologic history" ()
high climate variability: The major, recent, incredible advances, in human anatomical, behaviorial, habitat-related, and cultural evolution, are correlated with high cyclic climatic variations: "...tropical African climates [were] strongly influenced by insolation variability resulting from orbital procession cycles (19 & 23 kya)...[and further] modulated by eccentricity cycles (100 & 413 kya)...the interaction results in a predicted sequence of high and low climate variability in tropical Africa (confirmed by dust flux variance)..."