Английская Википедия:Galactic year

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The galactic year, also known as a cosmic year, is the duration of time required for the Sun to orbit once around the center of the Milky Way Galaxy.[1] One galactic year is approximately 225 million Earth years.[2] The Solar System is traveling at an average speed of 230 km/s (828,000 km/h) or 143 mi/s (514,000 mph) within its trajectory around the Galactic Center,[3] a speed at which an object could circumnavigate the Earth's equator in 2 minutes and 54 seconds; that speed corresponds to approximately 1/1300 of the speed of light.

The galactic year provides a conveniently usable unit for depicting cosmic and geological time periods together. By contrast, a "billion-year" scale does not allow for useful discrimination between geologic events, and a "million-year" scale requires some rather large numbers.[4]

Timeline of the universe and Earth's history in galactic years

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Файл:Motion of Sun, Earth and Moon around the Milky Way.jpg
The orientation of the Solar System's motion

The following list assumes that 1 galactic year is 225 million years.

Time Event
Galactic
years
(gal)
Millions
of years
(Ma)
Past (years ago)
About 61.32 gal Big Bang
About 54 gal Birth of the Milky Way
20.44 gal Birth of the Sun
17–18 gal 3937 Ma Oceans appear on Earth
16.889 gal 3800 Ma Life begins on Earth
15.555 gal 3500 Ma Prokaryotes appear
12 gal 2700 Ma Bacteria appear
10 gal 2250 Ma Eukaryian period[5][6] first appearance of eukaryotes[7] Stable continents appear
6.8 gal 1530 Ma Multicellular organisms appear
2.4 gal 540 Ma Cambrian explosion occurs
2 gal 500 Ma The first brain structure appears in worms
1.11 gal 250 Ma Permian–Triassic extinction event
0.2933 gal Cretaceous–Paleogene extinction event
0.0013 gal Emergence of anatomically modern humans
Future (years from now)
0.15 gal Mean time between impacts of asteroidal bodies in the order of magnitude of the K/Pg impactor has elapsed.[8]
1 gal All the continents on Earth may fuse into a supercontinent. Three potential arrangements of this configuration have been dubbed Amasia, Novopangaea, and Pangaea Ultima.[9]
2–3 gal Tidal acceleration moves the Moon far enough from Earth that total solar eclipses are no longer possible
4 gal Carbon dioxide levels fall to the point at which C4 photosynthesis is no longer possible. Multicellular life dies out[10]
15 gal Surface conditions on Earth are comparable to those on Venus today
22 gal The Milky Way and Andromeda Galaxy begin to collide
25 gal Sun ejects a planetary nebula, leaving behind a white dwarf
30 gal The Milky Way and Andromeda complete their merger into a giant elliptical galaxy called Milkomeda or Milkdromeda[11]
500 gal The Universe's expansion causes all galaxies beyond the Milky Way's Local Group to disappear beyond the cosmic light horizon, removing them from the observable universe[12]
2000 gal Local Group of 47 galaxies[13] coalesces into a single large galaxy[14]

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See also

References

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Шаблон:Star Шаблон:Time measurement and standards Шаблон:Chronology Шаблон:Portal bar