https://evolution.berkeley.edu/the-cambrian-explosion/
https://zh.wikipedia.org/zh-tw/%E5%AF%92%E6%AD%A6%E7%BA%AA%E5%A4%A7%E7%88%86%E5%8F%91
https://en.wikipedia.org/wiki/Cambrian_explosion
The Cambrian explosion (also known as Cambrian radiation[1] or Cambrian diversification) is an interval of time approximately 538.8 million years ago in the Cambrian period of the early Paleozoic when there was a sudden radiation of complex life, and practically all major animal phyla started appearing in the fossil record.[2][3][4] It lasted for about 13[5][6][7] to 25[8][9] million years and resulted in the divergence of most modern metazoan phyla.[10] The event was accompanied by major diversification in other groups of organisms as well.[a]
Before early Cambrian diversification,[b] most organisms were relatively simple, composed of individual cells, or small multicellular organisms, occasionally organized into colonies. As the rate of diversification subsequently accelerated, the variety of life became much more complex, and began to resemble that of today.[12] Almost all present-day animal phyla appeared during this period,[13][14] including the earliest chordates.[15]
A 2019 paper suggests that the timing should be expanded back to include the late Ediacaran, where another diverse soft-bodied biota existed and possibly persisted into the Cambrian, rather than just the narrower timeframe of the "Cambrian Explosion" event visible in the fossil record, based on analysis of chemicals that would have laid the building blocks for a progression of transitional radiations starting with the Ediacaran period and continuing at a similar rate into the Cambrian.[16]
寒武紀大爆發（亦稱寒武紀生命大爆發，Cambrian Explosion），是相對短時期的演化事件，開始於距今5.41億年前的寒武紀時期，化石記錄顯示絕大多數的動物「門」都在這一時期出現了[1][2]。它持續了2千萬年[3][4]-2.5千萬年[5][6]，它導致了大多數現代動物門的發散。 因出現大量的較高等生物以及物種多樣性，於是，這一情形被形象地稱為生命大爆發。這也是顯生宙的開始。在世界各地發現的化石群共同印證了這一生命演化史上的壯觀景象，例如在加拿大的伯吉斯頁岩，和在中國的帽天山頁岩(澄江化石地)，清江生物群等。這一時期的化石群相當典型，非常多的不同種類的生物幾乎同時在這一時期出現。
寒武紀大爆發的事實證據也曾讓達爾文非常困惑，在《物種起源》中寫道：「這件事情到現在為止都還沒辦法解釋。所以，或許有些人剛好就可以用這個案例，來駁斥我提出的演化觀點」。但即使到達爾文死後一百多年的今日，寒武紀大爆發依舊是科學界的一大謎題，尚待更多的科學證據出土，也許就能窺見當時的實際情況，找出真正的原因。
