Life

=== Fossils ===

{{main|Fossils}}

Fossils are the preserved remains or [[trace fossil|traces]] of organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in layers ([[stratum|strata]]) of [[sedimentary rock]] is known as the ''fossil record''. A preserved specimen is called a fossil if it is older than the arbitrary date of 10,000 years ago.<ref>{{cite web|url=http://www.sdnhm.org/science/paleontology/resources/frequent/|title=Frequently Asked Questions|publisher=San Diego Natural History Museum|access-date=25 May 2012|url-status=dead|archive-url=https://web.archive.org/web/20120510101706/http://sdnhm.org/science/paleontology/resources/frequent/|archive-date=10 May 2012}}</ref> Hence, fossils range in age from the youngest at the start of the [[Holocene]] Epoch to the oldest from the [[Archean|Archaean]] Eon, up to 3.4 [[1000000000 (number)|billion]] years old.<ref>{{cite news |first1=Brian |last1=Vastag |title=Oldest 'microfossils' raise hopes for life on Mars |date=21 August 2011 |url=https://www.washingtonpost.com/national/health-science/oldest-microfossils-hail-from-34-billion-years-ago-raise-hopes-for-life-on-mars/2011/08/19/gIQAHK8UUJ_story.html?hpid=z3 |newspaper=The Washington Post |access-date=21 August 2011 |url-status=live |archive-url=https://web.archive.org/web/20111019000458/http://www.washingtonpost.com/national/health-science/oldest-microfossils-hail-from-34-billion-years-ago-raise-hopes-for-life-on-mars/2011/08/19/gIQAHK8UUJ_story.html?hpid=z3 |archive-date=19 October 2011 }}</ref><ref>{{cite news |first=Nicholas |last=Wade |title=Geological Team Lays Claim to Oldest Known Fossils |date=21 August 2011 |url=https://www.nytimes.com/2011/08/22/science/earth/22fossil.html?_r=1&partner=rss&emc=rss&src=ig |work=The New York Times |access-date=21 August 2011 |url-status=live |archive-url=https://web.archive.org/web/20130501085118/http://www.nytimes.com/2011/08/22/science/earth/22fossil.html?_r=1&partner=rss&emc=rss&src=ig |archive-date=1 May 2013 }}</ref>