原文網址：https://news.vt.edu/articles/2024/12/science-extended-chart-of-life.html
By Kelly Izlar
根據維吉尼亞理工大學新的分析結果，遠古物種的演化速度可能較為緩慢且存活得更久，但是在涵蓋全球的冰河期結束之後演化的步調也跟著加快。這篇發表在期刊《科學》(Science)的研究，描繪出比恐龍古老許多倍的遠古生命崛起與衰亡的過程。
這幅簡化的圖表總結了整個元古宙真核生物多樣性的相對變化。圖片來源：Qing Tang of Nanjing University and Shuhai Xiao of Virginia Tech
如果整個世界是一座舞台而所有物種都是名演員，那麼在岩石紀錄當中便能找到他們上下場的時間。
骨骼與殼體化石清楚呈現了過去五億多年來，隨著時間推進生物是如何演化並走入滅絕。不過維吉尼亞理工大學的最新分析結果，又將這幅生命圖表的起點往前延伸到將近二十億年前。
這幅圖表顯示了物種數目的相對上升與下降，使科學家從中得知遠古生命的崛起、分化與滅絕的過程。
新的研究結果讓描繪生命演變的圖表現在也納入了元古宙(Proterozoic
Eon，距今2億5000萬年至5390萬年前)的生命形式。元古宙的生物通常體型較小且身形柔軟，像是海綿這種還未發展出礦物骨骼的生物，因此從先天上來說它們能留下來形成化石的事物並不多。
在12月20日發行的《科學》(Science)期刊當中，維吉尼亞理工學院的地質生物學家肖書海與合作學者根據從全世界彙整而來的化石數據，發表了他們對於元古宙全球生物多樣性的高解析度分析結果。
確切來說，肖書海和團隊的研究對象是古代海洋真核生物(擁有細胞核的生物)的化石紀錄。早期的真核生物日後演化成多細胞生物，而多細胞生物的出現成功帶領生命進入一個新的紀元，使得地球得以出現動物、植物與真菌。
「這是援用最新數據對該時期迄今最為透徹的分析結果，」不久之前入選為美國國家科學院院士的肖書海表示。「更重要的是，我們還運用了圖像對比程式，讓我們的時間解析度更加提升。」
物種的興衰就像一支舞蹈，從中我們可以對於地球環境演變與生命演化兩者之間的與時並進得出重要的見解。
這項分析觀察到的模式與提出的見解如下：
第一個真核生物至少在距今18億年前就已經出現，接著大約從14億5000萬年到7億2000萬年前，物種多樣性在逐漸演化到一個程度後便穩定下來——這段時期被稱為「無聊的十億年」(boring
billion)，正如其名此時的物種更迭速率低得驚人。
相較於之後才出現的真核生物種類，在「無聊的十億年」期間的種類可能演化得比較慢，存在的時間也更久。
然後浩劫降臨：在7億2000萬年到6億3500萬年前，氣溫急遽下降使得地球至少有兩次被完全冰封而成為「雪球地球」。當冰雪終於融化，演化也重拾活力，情況也不再枯燥乏味。
「從多樣性與演化動力學的角度來看，這段冰河期是重新設定演化路線的主因之一，」肖書海表示。「我們看到冰河期一結束真核生物的種類便迅速發生了交替，這是最主要的發現之一。」
肖書海表示此模式引起了許多有趣的問題，像是：
為什麼在「無聊的十億年」期間真核生物的演化停滯不前？
在雪球地球冰河期之後，造成演化步調提升的因素有哪些？
會是氣候變遷與大氣氧含量提升這類環境因素嗎？
還是不同物種之間的演化軍備競賽驅使生物快速演化？
未來科學家可以利用定量化的模式來回答這些問題，並且更加瞭解地球上的生物與地球本身之間錯綜複雜的交互作用。
Chart of life extended by nearly 1.5
billion years
Ancient species may have evolved slower
and lasted longer, but the pace of evolution accelerated after global ice ages,
according to a new Virginia Tech analysis. The study, published in the journal Science, maps the rise and fall of
ancient life many times older than the dinosaurs.
If all the world's a stage and all the species merely
players, then their exits and entrances can be found in the rock record.
Fossilized skeletons and shells clearly show how
evolution and extinction unfolded over the past half a billion years, but a new
Virginia Tech analysis extends the chart of life to nearly 2 billion years ago.
The chart shows the relative ups and downs in species
counts, telling scientists about the origin, diversification, and extinction of
ancient life.
With this new study, the chart of life now includes
life forms from the Proterozoic Eon, 2,500 million to 539 million years ago.
Proterozoic life was generally smaller and squishier — like sea sponges that
didn’t develop mineral skeletons — and left fewer traces to fossilize in the
first place.
Virginia Tech geobiologist Shuhai Xiao and
collaborators published a high-resolution analysis of the global diversity of
Proterozoic life based on a global compilation of fossil data, which was
released Dec. 20 in the journal Science.
Xiao and his team looked specifically at records of
ancient marine eukaryotes — organisms whose cells contain a nucleus. Early
eukaryotes later evolved into the multicellular organisms credited for ushering
in a whole new era for life on Earth, including animals, plants, and fungi.
“This is the most comprehensive and up-to-date
analysis of this period to date,” said Xiao who recently was inducted into the
National Academy of Sciences. “And more importantly, we’ve used a graphic
correlation program that allowed us to achieve greater temporal resolution.”
The choreography of species offers critical insights
into the parallel paths of the evolution of life and Earth.
Observed patterns and insights suggested by the
analysis:
The first eukaryotes arose no later than 1.8 billion
years ago and gradually evolved to a stable level of diversity from about 1,450
million to 720 million years ago, a period aptly known as the “boring billion,”
when species turnover rates were remarkably low.
Eukaryotic species in the “boring billion” may have
evolved slower and lasted longer than those came later.
Then cataclysm: Snowball Earth, a spiral of plunging
temperatures, sealed the planet in ice at least twice between 720 million and
635 million years ago. When the ice eventually thawed, evolutionary activity
picked up, and things weren’t so boring anymore.
“The ice ages were a major factor that reset the
evolutionary path in terms of diversity and dynamics,” Xiao said. “We see rapid
turnover of eukaryotic species immediately after glaciation. That’s a major
finding.”
The patterns, Xiao said, raise a lot of interesting
questions, including:
Why was eukaryotic evolution sluggish during the
“boring billion”?
What factors contributed to the increased pace of
evolution after snowball ice ages?
Was it environmental, such as climate changes and
increases in atmospheric oxygen level?
Was it an evolutionary arms race between different
organisms that could drive creatures to evolve quickly?
Future scientists can use the quantified pattern to
answer these questions and better understand the complex interplay of life on
Earth and the Earth itself.
原始論文：Qing Tang,
Wentao Zheng, Shuhan Zhang, Junxuan Fan, Leigh Anne Riedman, Xudong Hou, A. D.
Muscente, Natalia Bykova, Peter M. Sadler, Xiangdong Wang, Feifei Zhang, Xunlai
Yuan, Chuanming Zhou, Bin Wan, Ke Pang, Qing Ouyang, N. Ryan McKenzie, Guochun
Zhao, Shuzhong Shen, Shuhai Xiao. Quantifying the global biodiversity
of Proterozoic eukaryotes. Science, 2024; 386 (6728) DOI: 10.1126/science.adm9137
引用自：Virginia Tech. "Chart of life extended by
nearly 1.5 billion years."
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