研究解開地球第一批動物如何出現的謎團

原文網址：http://www.anu.edu.au/news/all-news/anu-led-study-solves-mystery-of-how-first-animals-appeared-on-earth

研究解開地球第一批動物如何出現的謎團

由澳洲國立大學(ANU)進行的研究解開了地球第一批動物如何出現的謎團，若地球沒有發生這齣重大事件則人類也不會存在。

領導此研究的副教授Jochen Brocks表示團隊在澳洲中部的古老沉積岩發現了答案。

澳洲國立大學地球科學研究中心的Brocks博士表示：「我們將岩石磨成粉後從中萃取出古代的有機物分子。」

「這些分子告訴我們事情在6億5000萬年前變得相當有趣。當時的生態系出現重大變革，也就是藻類的崛起。」

Brocks表示藻類崛起引發了地球史上影響最深遠的生態革命之一，若沒有發生此次事件則人類和其他動物都不會存在。

他說：「在這一切發生的5億年之前，發生了另一起稱作『雪球地球』的戲劇性事件。」

「在這5億年的時光中地球被徹底冰封。巨大的冰河覆蓋了整座山峰，將岩石磨碎後釋出內含的養分，之後全球溫度急速升高冰雪融化時，河川便將富含養分的洪流帶到海洋當中。」

Brocks博士表示海洋處於營養濃度極高的狀態，加上全球氣溫變涼到更適合生物居住的程度，創造出完美的環境條件讓藻類快速散佈至各處。他說這使得被細菌主宰的海洋轉變成一個有更複雜生物居住的世界。

Brocks博士表示：「這些位在食物鏈基層大型且營養豐富的生物，瞬間提供的大量能量讓複雜的生態系得以演化出來，給予體型越來越大且更加複雜的動物，包括人類在內存活於地球的基礎。」

共同主持的研究人員Amber Jarrett博士在澳洲中部發現的遠古沉積岩，含有的線索直接透露出雪球地球融化不久之後發生了什麼事件。

澳洲國立大學地球科學研究中心的博士後研究員Jarrett博士表示：「我們相當驚訝地發現這些岩石有分子化石的訊號。」

「我們立刻就明瞭我們有了突破性的發現：雪球地球直接參與了更大型且複雜生命的演化過程。」

這項研究刊登於《自然》( Nature)。

Study solves mystery of how first animals appeared on Earth

Research led by The Australian National University (ANU) has solved the mystery of how the first animals appeared on Earth, a pivotal moment for the planet without which humans would not exist.

Lead researcher Associate Professor Jochen Brocks said the team found the answer in ancient sedimentary rocks from central Australia.

"We crushed these rocks to powder and extracted molecules of ancient organisms from them," said Dr Brocks from the ANU Research School of Earth Sciences.

"These molecules tell us that it really became interesting 650 million years ago. It was a revolution of ecosystems, it was the rise of algae."  

Dr Brocks said the rise of algae triggered one of the most profound ecological revolutions in Earth's history, without which humans and other animals would not exist.

"Before all of this happened, there was a dramatic event 50 million years earlier called Snowball Earth," he said.

"The Earth was frozen over for 50 million years. Huge glaciers ground entire mountain ranges to powder that released nutrients, and when the snow melted during an extreme global heating event rivers washed torrents of nutrients into the ocean."

Dr Brocks said the extremely high levels of nutrients in the ocean, and cooling of global temperatures to more hospitable levels, created the perfect conditions for the rapid spread of algae. It was the transition from oceans being dominated by bacteria to a world inhabited by more complex life, he said.

"These large and nutritious organisms at the base of the food web provided the burst of energy required for the evolution of complex ecosystems, where increasingly large and complex animals, including humans, could thrive on Earth," Dr Brocks said.

Co-lead researcher Dr Amber Jarrett discovered ancient sedimentary rocks from central Australia that related directly to the period just after the melting of Snowball Earth.

"In these rocks we discovered striking signals of molecular fossils," said Dr Jarrett, an ANU Research School of Earth Sciences PhD graduate.

"We immediately knew that we had made a ground-breaking discovery that snowball Earth was directly involved in the evolution of large and complex life."

The research is published in Nature.

原始論文：Jochen J. Brocks, Amber J. M. Jarrett, Eva Sirantoine, Christian Hallmann, Yosuke Hoshino, Tharika Liyanage. The rise of algae in Cryogenian oceans and the emergence of animals. Nature, 2017; DOI: 10.1038/nature23457

引用自：Australian National University. "ANU-led study solves mystery of how first animals appeared on Earth."