Mesoproterozoic

The name and its history

International Precambrian Stratigraphy Subcommission / IUGS · 1990 ratification; 1991 publication

What does the word literally mean?

Paleo-, meso- and neo- identify oldest, middle and youngest subdivisions of the Proterozoic, respectively; the deeper protero-zoic element is itself historically relative to the Paleozoic.

What did the original author mean?

‘Middle’ positions the era between Paleoproterozoic and Neoproterozoic.

Why was the name needed?

A broadly usable international framework was required despite sparse worldwide biostratigraphic control.

What evidence supported the original concept?

The chosen numerical divisions were agreed institutionally, not deduced from a global middle-life turnover.

How has geology changed the concept?

Event-based revisions may modify subdivision boundaries without invalidating the term’s relational meaning.

Further historical context

The three-era subdivision and named Proterozoic periods were formalised in the 1991 account by K. A. Plumb on behalf of the international subcommission.

Because many lower boundaries are GSSAs fixed numerically rather than fossil-defined GSSPs, their Greek roots must not be treated as defining global events.

Editorial qualification

1991 ratification is established, but first individual usage of the full compound was not investigated.

Related names

Proterozoic · Paleoproterozoic · Neoproterozoic · Calymmian · Ectasian · Stenian · Fossil · Stratigraphy · GSSP

Sources

1. ICS International Chronostratigraphic Chart, 2026/06 — Current name, rank and numerical boundaries
2. Plumb (1991), New Precambrian time scale — 1991 ratification and nomenclature of Proterozoic subdivisions
3. Shields et al. (2021), revising the pre-Cryogenian time scale — Review of chronometric boundaries and historical meaning