Purpose
To provide a time span (from start to end) in millions of years for a geological period or pair of geological periods. The time span will automatically update when new information is available. The numerical part of the time span is linked to a graphical display.
Usage
There are two ways of using the template:
{{Period span/brief|period name|rounding (optional)}}{{Period span/brief|first period name|second period name|rounding (optional)}}.
Examples:
{{period span/brief|Pragian}}produces "413 to 411 million years ago" (without the quotes), i.e. the time from the start of the Pragian to the end of the Pragian{{period span/brief|Silurian|Carboniferous}}produces "443 to 299 million years ago", i.e. the time from the start of the Silurian to the end of the Carboniferous.
The last optional parameter can be set to 1, 2, etc. to display that number of decimal places, or to -1, -2, etc. to round to the nearest 10, 100, etc. years. The default is 0, i.e. no decimal places are shown. If you do want to display decimal places then, except for very recent times, you should probably instead use the template {{Period span}}, which avoids an impression of spurious accuracy by including error bounds. Note that decimal places will not be shown if they are not present in the source data.
Examples:
{{period span/brief|Pragian|1}}produces "413 to 410.6 million years ago"{{period span/brief|Pragian|-1}}produces "410 million years ago"; because the start and end round to the same number, only one is shown{{period span/brief|Silurian|Carboniferous|-1}}produces "440 to 300 million years ago".
Errors
If this template generates an error, it is likely to be because the period is missing from {{next period}} or {{period start}}. Please go ahead and add it in the appropriate place (once you've checked your spelling!).
You also need to add the period to {{period start error}} so that other templates which display geological dates, such as {{period span}}, which shows more details, will work properly.
Sources
For documentation on the sources of the dates and other information, see Template:Period start.
Period templates
This list is incomplete. You may help by expanding it