The Geologic Calendar is a scale in which the geological lifetime of the
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
is mapped onto a calendrical year; that is to say, the ''day one'' of the
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
took place on a geologic January 1 at precisely midnight, and today's date and time is December 31 at midnight.
On this calendar, the inferred appearance of the first living single-celled organisms,
prokaryote
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...
s, occurred on a geologic February 25 around 12:30pm to 1:07pm,
dinosaurs first appeared on December 13, the first flower plants on December 22 and the first primates on December 28 at about 9:43pm. The first
Anatomically modern humans
Early modern human (EMH) or anatomically modern human (AMH) are terms used to distinguish ''Homo sapiens'' (the only extant Hominina species) that are anatomically consistent with the range of phenotypes seen in contemporary humans from extin ...
did not arrive until around 11:48 p.m. on New Year's Eve, and all of human history since the
end of the last ice-age occurred in the last 82.2 seconds before midnight of the new year.
A variation of this analogy instead compresses Earth's 4.6 billion year-old history into a single day: While the Earth still forms at midnight, and the present day is also represented by midnight, the first life on Earth would appear at 4:00am, dinosaurs would appear at 10:00pm, the first flowers 10:30pm, the first primates 11:30pm, and modern humans would not appear until the last two seconds of 11:59pm.
A third analogy, created by University of Washington paleontologist Peter Ward and astronomer Donald Brownlee, who are both famous for their Rare Earth hypothesis, for their book ''The Life and Death of Planet Earth'', alters the calendar so it includes the Earth's future leading up to the Sun's death in the next 5 billion years. As a result, each month now represents 1 of 12 billion years of the Earth's life. According to this calendar, the first life appears in January, and the first animals first appeared in May, with the present day taking place on May 18, even though the Sun won't destroy Earth until December 31, all animals will die out by the end of May.
See also
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Cosmic Calendar
The Cosmic Calendar is a method to visualize the chronology of the universe, scaling its currently understood age of 13.8 billion years to a single year in order to help intuit it for pedagogical purposes in science education or popular science.
...
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Calendar
A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A date is the designation of a single and specific day within such a system. A calendar is also a physi ...
References
Units of time
Physical cosmology
Time in astronomy
Calendar
A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A date is the designation of a single and specific day within such a system. A calendar is also a physi ...
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