Galactic year
The galactic year, also known as a cosmic year, is the duration of time required for the
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
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 | 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 Pangaea Ultima.[9]
| |
2–3 gal | 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 Milkdromeda[11]
| |
500 gal | The Universe's expansion causes all galaxies beyond the Milky Way's 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] |
See also
References
- ^ Cosmic Year Archived 2014-04-12 at the Wayback Machine, Fact Guru, University of Ottawa
- ^ Leong, Stacy (2002). "Period of the Sun's Orbit around the Galaxy (Cosmic Year)". The Physics Factbook.
- ^ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question18.html NASA – StarChild Question of the Month for February 2000
- ^ Geologic Time Scale – as 18 galactic rotations
- PMID 24963687.
- S2CID 4331375.[permanent dead link]
- OCLC 808340848.
- ^ Lunar and Planetary Institute (2010), https://www.lpi.usra.edu/features/chicxulub/
- ^ Williams, Caroline; Nield, Ted (2007-10-17). "Pangaea, the comeback". New Scientist. Retrieved 2014-01-02.
- S2CID 3619702.
- S2CID 14964036.
- S2CID 118750775.
- ^ Frommert, Hartmut; Kronberg, Christine (2007-06-05). "The Local Group of Galaxies". University of Arizona. Students for the Exploration and Development of Space. Archived from the original on 2009-09-07. Retrieved 2009-10-02.
- S2CID 12173790.
- ^ "Milky Way Past Was More Turbulent Than Previously Known". ESO News. European Southern Observatory. 2004-04-06.
After more than 1,000 nights of observations spread over 15 years, they have determined the spatial motions of more than 14,000 solar-like stars residing in the neighbourhood of the Sun.