地球史

出自維基百科，自由嘅百科全書
跳去導覽 跳去搵嘢
Earth's history with time-spans of the eons to scale

地球史，係地球呢粒行星由形成嗰時一路到今時今日嘅發展歷史。[1][2]

冇爭議嘅最早期嘅證據顯示，喺而今35億年前已經有生命存在。[3][4][5]

早期嘅地球[編輯]

根據放射測年法（Radiocarbon dating）嘅測量結果，太陽系大約係喺 45.6 ± 0.08 億年之前成形嘅[6]，原生嘅地球大約喺 45.4 ± 0.04 億年前成形[7]。一般認為，太陽嘅形成喺大約 46 億年前，嗰時一舊好大舊嘅氫分子雲嘅引力坍縮（Gravitational collapse；一舊天體因為自己嘅重力而向內收縮嘅現象），坍縮嘅質量集中喺佢中心嗰度，而呢啲氫分子可以做核聚變（Nuclear fusion；氫原子撞埋一齊變做啲更大粒嘅化學元素）嚟釋放龐大嘅光同熱能－呢團大舊嘅氫就形成咗太陽。淨低嗰啲部份一邊旋轉一邊攤平，形成咗一大團圍住後生嘅太陽轉嘅粒子（即係所謂嘅原行星盤；Protoplanetary disk）。呢團粒子遲吓就會變做行星、衛星、流星體、同其他太陽系嘅小天體－經個 1000 至 2000 萬年嘅演化，最後形成咗原生地球[8]。初頭地球完全唔啱生物住－佢嗰時個表面恐怕係一個由岩漿組成嘅「海」。

月球形成[編輯]

月球大約喺 45.3 億年前形成[9]。關於月球起源嘅機制而家仲未有乜嘢定論。一個好受歡迎嘅假說係大碰撞說（Giant impact hypothesis）[10]：呢個諗法認為有一粒好似火星噉大，質量係地球 1/10 嘅天體撞落地球度。呢吓碰撞引發咗大爆炸，炸到地球入面好多物質飛咗上太空，經過吸積作用形成咗月球，而嗰粒天體嘅部份物質亦都熔咗入地球度。而喺打後嘅 41 億至 38 億年前嘅嗰段時間，無數嘅小行星撞落月球嘅表面，令到月球嘅表面變得好犀利，而且當時嘅地球似乎都係成日俾小行星撞。

冷卻凝固[編輯]

由太古宙（Archean；指 40 億年前至 25 億年前嘅時代）嗰陣開始，地球嘅表面開始冷卻凝固，形成咗硬淨嘅岩石[11]，而火山爆發會釋放出一啲氣體，形成咗一個原始嘅大氣圈。呢個大氣圈會有水蒸氣、二氧化碳、同氮組成，水汽嘅蒸發令到地表冷卻得更加快。冷卻到噉上下，暴雨連續落咗成千上萬年，呢啲雨水灌滿咗盆地，形成咗個海。呢場大暴雨減少咗空氣入面嘅水汽含量，仲洗走咗大氣入面好多二氧化碳[12]。除咗噉，小行星、原行星、彗星上面嘅水同冰亦都帶咗啲水嚟地球[13]。當時嘅太陽似乎弱過而家，但係當時大氣入面嘅温室氣體令到地球保持到一定嘅温度，個新形成嘅海應該唔會結嗮冰[14]。

跟住落嚟，地球嘅其餘物理同化學性質開始漸漸噉成形。大約喺 35 億年前，地球有咗佢股磁場，佢幫到手令到太陽風唔會正面吹襲地球嘅大氣，令到大氣層嘅粒子冇噉容易俾太陽風吹到離開地球[15]。地球嘅外層冷卻凝固，喺大氣層水汽嘅作用之下形成地殼。至於陸地係點嚟，科學界有兩個模型解釋[16]：一種認為陸地到咗家吓仲係增長緊[17]；而另一種更加可能嘅模型認為地球歷史早期嘅陸地迅速噉生成，然後保持到而家[18][19][20][21]。

嗰陣時，地球內部嘅熱量係噉散走，驅動板塊構造運動，形成大陸，經過幾億年，超大陸（Supercontinent）經歷三次嘅分分合合－啲大陸板塊黐埋又分開，最近嘅盤古大陸（Pangaea）喺大約 1.8 億年前分裂[22]。到咗今日，呢種地殼活動仲喺度進行緊。

絕咗種嘅節肢動物 Marrella 嘅化石；喺寒武紀嗰陣，地球突然多咗好多生物品種。

生命起源[編輯]

內文：生命起源

地球係目前宇宙已知行星入面唯一能夠維持生命嘅[23]。一般認為大約 40 億年前嘅高能化學反應產生咗能夠複製自己嘅分子，打後 5 億年就出現咗所有生命嘅共同祖先，再分化咗細菌同古菌出嚟[24]。早期嘅生命體發展出搞光合作用嘅能力，於是有得直接利用太陽能向大氣嗰度釋放啲氧氣。大氣度積累嘅氧氣俾太陽射嘅紫外線作用，喺上層大氣形成咗臭氧（O3），出現咗臭氧層[25]。早期嘅生命以原核生物（Prokaryote；以單一原核細胞組成嘅生物）嘅形態存在。由於臭氧層吸收咗太陽射落嚟嘅紫外線，陸地變到好啱生命生存，所以生命開始喺陸地上面繁衍[26]。目前已知最早嘅生命化石證據有西澳洲砂岩入面揾到嘅 34.8 億年前嘅微生物墊化石[27][28][29][30]、西格陵蘭變質碎屑岩度 37 億年前嘅生源石墨[31]、仲有西澳洲岩石度 41 億年前嘅生物質殘骸[32]。

距離而家大約 5.42 億年前發生咗寒武紀生命大爆發（Cambrian explosion）。由化石睇，嗰時地球上嘅多細胞生物種類突然之間多咗好多，包括節肢動物（Arthropods）三葉蟲、奇蝦等[33]。化石記錄顯示大多數嘅動物門都係喺呢個時期出現嘅[34][35]。呢個時期持續咗大約 2 千萬年至 2 千 5 百萬年，導致咗大多數現代動物門嘅發散。複雜啲嘅生物多咗好多，生物多樣性大幅噉提高，所以佢俾人話係生命嘅大爆發。

喺後少少嘅 5 億年前嘅奧陶紀（Ordovician）地球有咗脊椎動物（Vertebrates）－甲冑魚（Ostracoderms）。打後嘅化石記錄顯示地球又有咗幾次生物物種嘅大規模增加或者滅絕[36]，最近嗰次係 6 千 6 百萬年前嘅白堊紀-古近紀滅絕事件（Cretaceous–Paleogene extinction event），呢次事件引致咗恐龍嘅滅絕，但係一啲細隻嘅動物－當中有哺乳類－走得甩死唔去，令到地球嘅生命持續落去。嗰次之後，哺乳類開始變到愈嚟愈發達，而幾百萬年前嘅非洲嘅類猿（Ape）動物似乎開始用兩隻腳行，空咗對手出嚟令到佢哋可以整工具，個腦又變到愈嚟愈大－慢慢進化成智人（Homo sapien）[37]。智人嘅各種活動產生咗世界嘅各大文明同科技。

各種猿類動物（包括人）嘅骨骼

參考[編輯]

  1. ↑ Stanley 2005
  2. ↑ Gradstein, Ogg & Smith 2004
  3. ↑ Schopf, J. William; Kudryavtsev, Anatoliy B.; Czaja, Andrew D.; Tripathi, Abhishek B. (5 October 2007). "Evidence of Archean life: Stromatolites and microfossils". Precambrian Research. Amsterdam, the Netherlands: Elsevier. 158 (3–4): 141–155. Bibcode:2007PreR..158..141S. doi:10.1016/j.precamres.2007.04.009. ISSN 0301-9268.
  4. ↑ Schopf, J. William (29 June 2006). "Fossil evidence of Archaean life". Philosophical Transactions of the Royal Society B. London: Royal Society. 361 (1470): 869–885. doi:10.1098/rstb.2006.1834. ISSN 0962-8436. PMC 1578735. PMID 16754604.
  5. ↑ Raven & Johnson 2002, p. 68
  6. ↑ Bowring, S.; Housh, T. The Earth's early evolution. Science. 1995, 269 (5230): 1535–40.
  7. ↑ The Age of the Earth
  8. ↑ Yin, Q.; Jacobsen, S. B.; Yamashita, K.; Blichert-Toft, J.; Télouk, P.; Albarède, F. A short timescale for terrestrial planet formation from Hf-W chronometry of meteorites. Nature. 2002, 418 (6901): 949–52.
  9. ↑ Kleine, T.; Palme, H.; Mezger, K.; Halliday, A. N. Hf-W Chronometry of Lunar Metals and the Age and Early Differentiation of the Moon. Science. 2005-11-24, 310 (5754): 1671–74.
  10. ↑ Jones, J. H. Tests of the Giant Impact Hypothesis (PDF). Lunar and Planetary Science. Origin of the Earth and Moon Conference. Monterey, California. 1998.
  11. ↑ The Proterozoic, Archean and Hadean are often collectively referred to as the Precambrian Time or sometimes, also the Cryptozoic.
  12. ↑ 孫樹遠 汪勤模. 大氣的起源. 中國氣象報. 1989.
  13. ↑ Morbidelli, A.; et al. Source regions and time scales for the delivery of water to Earth. Meteoritics & Planetary Science. 2000, 35 (6): 1309–20.
  14. ↑ Guinan, E. F.; Ribas, I. Benjamin Montesinos, Alvaro Gimenez and Edward F. Guinan, Ed. Our Changing Sun: The Role of Solar Nuclear Evolution and Magnetic Activity on Earth's Atmosphere and Climate. ASP Conference Proceedings: The Evolving Sun and its Influence on Planetary Environments (San Francisco: Astronomical Society of the Pacific).
  15. ↑ Oldest measurement of Earth's magnetic field reveals battle between Sun and Earth for our atmosphere
  16. ↑ Rogers, J. J. W.; Santosh, M. Continents and Supercontinents. Oxford University Press US. 2004: 48.
  17. ↑ Hurley, P. M.; Rand, J. R. Pre-drift continental nuclei. Science. Jun 1969, 164 (3885): 1229–42.
  18. ↑ De Smet, J.; Van Den Berg, A.P.; Vlaar, N.J. Early formation and long-term stability of continents resulting from decompression melting in a convecting mantle. Tectonophysics. 2000, 322 (1–2): 19–33.
  19. ↑ Harrison, T.; et al. Heterogeneous Hadean hafnium: evidence of continental crust at 4.4 to 4.5 ga. Science. December 2005, 310 (5756): 1947–50.
  20. ↑ Hong, D.; Zhang, J.; Wang, T.; Wang, S.; Xie, X. Continental crustal growth and the supercontinental cycle: evidence from the Central Asian Orogenic Belt. Journal of Asian Earth Sciences. 2004, 23 (5): 799–813.
  21. ↑ Armstrong, R. L. The persistent myth of crustal growth. Australian Journal of Earth Sciences. 1991, 38 (5): 613–30.
  22. ↑ Murphy, J. B.; Nance, R. D. How do supercontinents assemble?. American Scientist. 1965, 92 (4): 324–33.
  23. ↑ Purves, W. K.; Sadava, D.; Orians, G. H.; Heller, C. Life, the Science of Biology: The Science of Biology. Macmillan. 2001: 455.
  24. ↑ Doolittle, W. F.; Worm, B.. Uprooting the tree of life (PDF). Scientific American. February 2000, 282 (6): 90–95.
  25. ↑ Zimmer, C. Earth’s Oxygen: A Mystery Easy to Take for Granted. New York Times. 2013-10-03 [2013-10-03].
  26. ↑ Burton, K. Astrobiologists Find Evidence of Early Life on Land. NASA.
  27. ↑ Schopf, J. W.; Kudryavtsev, A. B.; Czaja, A. D.; Tripathi, A. B. Evidence of Archean life: Stromatolites and microfossils. Precambrian Research (Amsterdam, the Netherlands: Elsevier). 2007-10-05, 158 (3–4): 141–155.
  28. ↑ Schopf, J. W. Fossil evidence of Archaean life. Philosophical Transactions of the Royal Society B (London: 皇家學會). 2006-06-29, 361 (1470): 869–885.
  29. ↑ Noffke, Nora; Christian, Daniel; Wacey, David; Hazen, Robert M. Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia. Astrobiology (journal). 2013-11-08, 13 (12): 1103–24 [2013-11-15].
  30. ↑ Oldest fossil found: Meet your microbial mom
  31. ↑ Ohtomo, Y.; Kakegawa, T.; Ishida, A.; et al. Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks. Nature Geoscience (London: 自然出版集團). January 2014, 7 (1): 25–28.
  32. ↑ Borenstein, S. Hints of life on what was thought to be desolate early Earth. Excite (Yonkers, NY: Mindspark Interactive Network). Associated Press. 2015-10-19 [2015-10-20].
  33. ↑ Kirschvink, J. L. Schopf, J.W.; Klein, C. and Des Maris, D, Ed. Late Proterozoic low-latitude global glaciation: the Snowball Earth. The Proterozoic Biosphere: A Multidisciplinary Study. Cambridge University Press. 1992: 51–52.
  34. ↑ Maloof, A. C.; Porter, S. M.; Moore, J. L.; Dudas, F. O.; Bowring, S. A.; Higgins, J. A.; Fike, D. A.; Eddy, M. P. The earliest Cambrian record of animals and ocean geochemical change. Geological Society of America Bulletin. 2010, 122 (11–12): 1731–1774.
  35. ↑ New Timeline for Appearances of Skeletal Animals in Fossil Record Developed by UCSB Researchers
  36. ↑ Raup, D. M.; Sepkoski Jr, J. J. Mass Extinctions in the Marine Fossil Record. Science. 1982, 215 (4539): 1501–03.
  37. ↑ Wilkinson, B. H.; McElroy, B. J. The impact of humans on continental erosion and sedimentation. Bulletin of the Geological Society of America. 2007, 119 (1–2): 140–56 [2007-04-22].

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