Geology.com. The USGS has released an updated Geological Time Scale. One noteworthy revision is that the Ediacaran ( 635 mya - 542 mya) has become the first formally recognized geological unit (system) of the Proterozoic. Division of time into geological units like the now recognized Ediacaran are based on some natural break in earth conditions.
In the case of the Ediacaran the unit is recognized on the basis of the unique fauna it contains - among the first examples of multicellular animals have been preserved in these strata and this unique fauna has been found to have a global distribution between 635 million years ago and 542 million years ago. That makes the Ediacaran worthy of a status of a formal geological division. The stratigraphic section in which these conditions are best represented and in which the beginning and end of these unique conditions are well preserved is called a type section or a stratotype. The type section for Ediacaran is in the Ediacara Hills Flinders Ranges of south Australia.
Other changes include revisions to the base of the Holocene series/epoch and the base of the Pleistocene series/epoch. You can download the USGS fact sheet on the revised Geological Time Scale here.