在地层学、古生物学、地质学和地球生物学中，界（erathem）是在地质年代中某一“代”的相应时间跨度内沉积的地层总单位。
因此，它可用作年代地层的时间单位，勾勒出一个大跨度的期间，小于“宇”，但大于后续依次更小和更精细的划分（系、统和阶）。到35亿年前，地球上已经发展出了简单的生命（澳大利亚已知最古老的微生物化石可追溯到该年代））。
一些简单的有机体，蓝藻统治了仍在冷却的地球近1亿年。
另请查看
多学科比较
其他相关议题
*欧洲新近纪哺乳动物
*地质年代
**新西兰地质年代
*北美陆生哺乳动物时代
*动物区系(动物)
*典型区域
备注
参考文献
*
- Hedberg, H.D., (editor), International stratigraphic guide: A guide to stratigraphic classification, terminology, and procedure, New York, John Wiley and Sons, 1976
- [http://www.stratigraphy.org/cheu.pdf International Stratigraphic Chart] from the International Commission on Stratigraphy
- [https://web.archive.org/web/20080923230940/http://www.nature.nps.gov/geology/USGSNPS/gtime/gtime1.html US National Park Service description of geographic time]
- [http://astro.wsu.edu/worthey/earth/html/md08.html Washington State University description of geographic time]
- [http://www.ucmp.berkeley.edu/help/timeform.html Web Geological Time Machine]
- [https://web.archive.org/web/20100618055137/http://pballew.net/arithm16.html#aeon Eon or Aeon], [https://web.archive.org/web/20100724212222/http://www.pballew.net/etyindex.html Math Words – An alphabetical index]
外部链接
*[http://www.stratigraphy.org/over.htm The Global Boundary Stratotype Section and Point (GSSP)] : overview
*[http://stratigraphy.science.purdue.edu/gssp/index.php?parentid=all Chart of The Global Boundary Stratotype Sections and Points (GSSP)] : chart
*[http://www.rocksandminerals.com/geotime/geotime.htm Geotime chart displaying geologic time periods compared to the fossil record] – Deals with chronology and classifications for laymen (not GSSPs)
评论 (0)