In the geologic timescale, the Ludfordian is the age of the Ludlow epoch of the Silurianperiod of the Paleozoicera of the Phanerozoiceon that is comprehended between 421.3 ± 2.6Ma and 418.7 ± 2.7 Ma (million years ago), approximately. The Ludfordian age succeeds the Gorstian age and precedes the Pridoli epoch. The Lau Event is a rapid pulse of cooling during the Ludfordian, about 420 million years ago; it is identified by a pulse of extinctions and oceanic changes. It is one of the series of fast sea-level and excursions in oxygen isotope ratios that signal fast switches between warm and cold climate states, characteristic of the Silurian climatic instability. The Lau Event occurred during an extended period of elevated seawater saturation state, explained by reservoirs of the planet's fresh water being locked up in massive polar ice caps. The sudden reappearance in normally saline marine environments of stromatolites and a mass occurrence of oncoids during the event suggested that minor extinction events like the Lau Event also resulted in periods of reduced grazing pressures on surviving "disaster biota", which can be compared to the aftermath of the more catastrophic end-Ordovician and end-Permian mass extinctions.[1] The geologic time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth. ... A geologic age is a time period on the geologic timescale delimited by major geologic or paleontologic events. ... This article is about the town in Shropshire, England. ... For other uses, see Silurian (disambiguation). ... In geology, a period or age is a time span of many millions of years that are assumed to have had similar characteristics. ... The Paleozoic Era (from the Greek palaio, old and zoion, animals, meaning ancient life) is the earliest of three geologic eras of the Phanerozoic eon. ... The table and timeline of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy. ... During the Phanerozoic the biodiversity shows a steady but not monotonic increase from near zero to several thousands of genera. ... In general usage, an eon (sometimes spelled aeon) is a very long period of time. ... Annum is a Latin noun meaning year. ... In the geologic timescale, the Gorstian is the age of the Ludlow epoch of the Silurian period of the Paleozoic era of the Phanerozoic eon that is comprehended between 422. ... In the geological timescale, the Pridoli epoch (from 418. ... The Lau event was the last of three relatively minor mass extinctions during the Silurian period, and is marked by an excursion in geochemical isotopes and a change in depositional regime. ... Pre-Cambrian stromatolites in the Siyeh Formation, Glacier National Park. ...
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