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Galactic year

Unit of time

Unit of time

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. One galactic year is approximately 225 million Earth years. 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, 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 convenient medial 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.

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

Main article: Timeline of the early universe, Timeline of natural history, Timeline of the far future

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

TimeEventGalactic
years
(gal) (approx.)Millions of years (Ma) (approx.)Past (years ago)Future (years from now)
61 gal13725 Ma (13.7 Ga)Big Bang
60 gal13500 Ma (13.5 Ga)Birth of the Milky Way
49 gal11025 Ma (11 Ga)A hypothesized merge of Milky Way with Kraken galaxy
20 gal4500 MaBirth of the Sun and Earth
17–18 gal3825–4050 MaOceans appear on Earth
17 gal3825 MaLife begins on Earth
16 gal3600 MaProkaryotes appear
12 gal2700 MaBacteria appear
11 gal2475 MaThe Great Oxidation Event commences
10 gal2250 Malast1=El Albanifirst1=Abderrazaklast2=Bengtsonfirst2=Stefanlast3=Canfieldfirst3=Donald E.last4=Riboulleaufirst4=Armellelast5=Rollion Bardfirst5=Clairelast6=Macchiarellifirst6=Robertodisplay-authors=etalyear=2014title=The 2.1 Ga Old Francevillian Biota: Biogenicity, Taphonomy and Biodiversityjournal=PLOS ONEvolume=9issue=6article-number=e99438bibcode=2014PLoSO...999438Edoi=10.1371/journal.pone.0099438pmc=4070892pmid=24963687doi-access=free}} first appearance of eukaryotes Stable continents appear
7 gal1575 MaMulticellular organisms appear
5 gal1125 MaMeiosis and sexual reproduction appear
4 gal900 MaFirst multicellular terrestrial plants
3 gal675 MaPossible early animals (Animalia)
2 gal540 MaCambrian explosion occurs
2 gal500 MaThe first brain structure appears in worms
1 gal225 MaPermian–Triassic extinction event
0.3 gal68 MaCretaceous–Paleogene extinction event
0.001 gal0.23 MaEmergence of anatomically modern humans
0.15 gal34 MaMean time between impacts of asteroidal bodies in the order of magnitude of the K/Pg impactor has elapsed.
1 gal225 MaAll the continents on Earth may fuse into a supercontinent. Three potential arrangements of this configuration have been dubbed Amasia, Novopangaea, and Pangaea Proxima.
2–3 gal450–675 MaTidal acceleration moves the Moon far enough from Earth that total solar eclipses are no longer possible
4 gal900 MaCarbon dioxide levels fall to the point at which C4 photosynthesis is no longer possible. Multicellular life dies out
15 gal3375 MaSurface conditions on Earth are comparable to those on Venus today
22 gal4950 MaThe Milky Way and Andromeda Galaxy begin to collide
25 gal5625 MaSun ejects a planetary nebula, leaving behind a white dwarf
30 gal6750 MaThe Milky Way and Andromeda complete their merger into a giant elliptical galaxy called Milkomeda or Milkdromeda
500 gal112500 Ma (112.5 Ga)The Universe's expansion causes all galaxies beyond the Milky Way's Local Group to disappear beyond the cosmic event horizon, removing them from the reachable universe
2000 gal450000 Ma (450 Ga)Local Group of 47 galaxies coalesces into a single large galaxy

References

References

  1. [http://www.csi.uottawa.ca:4321/astronomy/index.html#cosmicyear Cosmic Year] {{webarchive. link. (2014-04-12 , Fact Guru, [[University of Ottawa]])
  2. Leong, Stacy. (2002). "Period of the Sun's Orbit around the Galaxy (Cosmic Year)". The Physics Factbook.
  3. http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question18.html NASA – StarChild Question of the Month for February 2000
  4. [http://www.vendian.org/mncharity/dir3/geologic_time_galactic Geologic Time Scale – as 18 galactic rotations]
  5. (October 2020). "Kraken reveals itself – the merger history of the Milky Way reconstructed with the E-MOSAICS simulations". Monthly Notices of the Royal Astronomical Society.
  6. Young, Monica. (November 13, 2020). "Star Clusters reveal the "Kraken" in the Milky Way's Past".
  7. Dalrymple, G. Brent (2001). "The age of the Earth in the twentieth century: a problem (mostly) solved". Geological Society, London, Special Publications. 190 (1): 205–221.
  8. Buick, Roger (August 27, 2008). "When did oxygenic photosynthesis evolve?". Philosophical Transactions of the Royal Society B. 363 (1504): 2731–2743.
  9. (2014). "The 2.1 Ga Old Francevillian Biota: Biogenicity, Taphonomy and Biodiversity". PLOS ONE.
  10. (2010). "Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago". Nature.
  11. F. M. Gradstein. (2012). "The geologic time scale 2012. Volume 2". Elsevier.
  12. Bernstein, Harris; Bernstein, Carol; Michod, Richard E. (2012). "DNA Repair as the Primary Adaptive Function of Sex in Bacteria and Eukaryotes". In Kimura, Sakura; Shimizu, Sora (eds.). DNA Repair: New Research. Hauppauge, NY: Nova Science Publishers. ISBN 978-1-62100-808-8. LCCN 2011038504. OCLC 828424701.
  13. (26 May 2011). "Earth's earliest non-marine eukaryotes". Nature.
  14. Zimmer, Carl. (27 November 2019). "Is This the First Fossil of an Embryo? - Mysterious 609-million-year-old balls of cells may be the oldest animal embryos — or something else entirely.". [[The New York Times]].
  15. Cunningham, John A.. (5 December 2016). "The origin of animals: Can molecular clocks and the fossil record be reconciled?". [[BioEssays]].
  16. Lunar and Planetary Institute (2010), https://www.lpi.usra.edu/features/chicxulub/
  17. (2007-10-17). "Pangaea, the comeback". New Scientist.
  18. (2005-11-07). "Causes and timing of future biosphere extinction". Copernicus GmbH.
  19. (2008-05-01). "The collision between the Milky Way and Andromeda". Oxford University Press (OUP).
  20. Loeb, Abraham. (2011-04-18). "Cosmology with hypervelocity stars". IOP Publishing.
  21. (2007-06-05). "The Local Group of Galaxies". Students for the Exploration and Development of Space.
  22. (1997-04-01). "A dying universe: the long-term fate and evolutionof astrophysical objects". Reviews of Modern Physics.
  23. (2004-04-06). "Milky Way Past Was More Turbulent Than Previously Known". [[European Southern Observatory]].
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