地球礦物，宇宙僅有

原文網址：www.sciencedaily.com/releases/2015/08/150826113615.htm

Earth's mineralogy unique in the cosmos

地球礦物，宇宙僅有

New research from a team led by Carnegie's Robert Hazen predicts that Earth has more than 1,500 undiscovered minerals and that the exact mineral diversity of our planet is unique and could not be duplicated anywhere in the cosmos.

由卡內基大學的Robert Hazen領軍的團隊發表的新研究，預測地球上還有1500種礦物尚待發現，且地球獨一無二的礦物多樣性在宇宙中可說絕無僅有。

Minerals form from novel combinations of elements. These combinations can be facilitated by both geological activity, including volcanoes, plate tectonics, and water-rock interactions, and biological activity, such as chemical reactions with oxygen and organic material.

化學元素以各種方式組合而形成了礦物。地質活動和生物活動都能夠幫助這些組合發生，前者包括了火山活動、板塊構造作用、水岩交互作用(water-rock interaction)；後者像是氧氣和有機物參與其中的化學反應。

Nearly a decade ago, Hazen developed the idea that the diversity explosion of planet's minerals from the dozen present at the birth of our Solar System to the nearly 5,000 types existing today arose primarily from the rise of life. More than two-thirds of known minerals can be linked directly or indirectly to biological activity, according to Hazen. Much of this is due to the rise of bacterial photosynthesis, which dramatically increased the atmospheric oxygen concentration about 2.4 billion years ago.

將近十年前Hazen發展出一套理論認為，地球的礦物種類能從太陽系剛形成時的寥寥無幾，暴增至現今將近有5000種的主因為生命出現在地球上。據Hazen說，三分之二的已知礦物或多或少都跟生物活動有直接或間接關連。其中大多數又因細菌發展出光合作用而生，此作用在24億年前大幅增加了大氣中的氧氣含量。

In a suite of four related, recently published papers, Hazen and his team--Ed Grew, Bob Downs, Joshua Golden, Grethe Hystad, and Alex Pires--took the mineral evolution concept one step further. They used both statistical models of ecosystem research and extensive analysis of mineralogical databases to explore questions of probability involving mineral distribution.

Hazen和他研究小組的組員，Ed Grew、Bob Downs、Joshua Golden、Grethe Hystad、Alex Pires最近發表了四篇彼此相關的論文，進一步發展礦物演化論的概念。他們利用了生態學研究用的統計模型，並大量分析礦物資料庫來探討礦物分布的概率。

They discovered that the probability that a mineral "species" (defined by its unique combination of chemical composition and crystal structure) exists at only one locality is about 22 percent, whereas the probability that it is found at 10 or fewer locations is about 65 percent. Most mineral species are quite rare, in fact, found in 5 or fewer localities.

他們發現在所有的礦物種類(定義上為擁有獨特的化學元素組成與結晶構造)中，僅分布在一個地點的礦物約為22%，分布在十個或以下地點的約為65%。事實上大多數的礦物都十分稀有，分布地點為五個或少於五個。

"Minerals follow the same kind of frequency of distribution as words in a book," Hazen explained. "For example, the most-used words in a book are extremely common such as 'and,' 'the,' and 'a.' Rare words define the diversity of a book's vocabulary. The same is true for minerals on Earth. Rare minerals define our planet's mineralogical diversity."

「礦物分佈的機率跟字彙在書中的分佈模式相去不遠。」Hazen解釋。「舉例來說，在一本書中會有些頻繁出現的單字，像是「and」、「then」、「a」。然而偶爾出現的單字才是決定一本書字彙豐富程度的關鍵。地球上的礦物也是如此，罕見礦物決定了我們星球的礦物豐富程度。」

Further statistical analysis of mineral distribution and diversity suggested thousands of plausible rare minerals either still await discovery or occurred at some point in Earth's history, only to be subsequently lost by burial, erosion, or subduction back into the mantle. The team predicted that 1,563 minerals exist on Earth today, but have yet to be discovered and described.

進一步統計分析礦物的分佈模式與多樣性，結果顯示可能還有數千種礦物等著我們去發現，或是它們曾存在於地球歷史中的某段時光，如今卻因為埋藏、侵蝕或隨著隱沒作用回到地函而消失。團隊預測當今在地球上還有1563種礦物未被人類發現及描述。

The distribution of these "missing" minerals is not uniform, however.

但這些消失的礦物並非均勻分佈在這個世界上。

Several circumstances influence the likelihood of a mineral having previously been discovered. This includes physical characteristics, such as color. White minerals are less likely to have been noticed, for example. Other factors include the quality of crystallization, solubility in water, and stability near the surface of the planet.

在已辨識出來的礦物中，有幾個要素會決定發現它們的可能性，這包括了幾項物理特徵。比方說顏色，白色的礦物相對而言不那麼引人注目。其它因素還包含了結晶的品質優劣、在水中的溶解度，還有接近地表時的穩定程度。

As such, Hazen and his colleagues predicted that nearly 35 percent of sodium minerals remain undiscovered, because more than half of them are white, poorly crystallized, or water soluble. By contrast, fewer than 20 percent of copper, magnesium, and copper minerals have not been discovered.

因為如此，Hazen與他的同僚預估有將近35%的含鈉礦物仍未被發現，它們的外觀多半為白色、結晶甚差，或者易溶於水。相較之下，含銅、鎂的礦物未被發現者則小於20%。

Further expanding the link between geological and biological evolution, Hazen's team applied the biological concepts of chance and necessity to mineral evolution. In biology, this idea means that natural selection occurs because of a random "chance" mutation in the genetic material of a living organism that becomes, if it confers reproductive advantage, a "necessary" adaptation.

Hazen的團隊將生物學中的偶然性和必然性概念應用在礦物演化上，而更加擴展了地質學與生物演化之間的關連。在生物學上，此概念意味著若生命體的基因物質中出現的「隨機」突變可以讓牠們更順利的繁衍後代，那麼這突變「必然」會成為生物體的適應(adaptation)，天擇因而發生。

But in this instance, Hazen's team asked how the diversity and distribution of Earth's minerals came into existence and the likelihood that it could be replicated elsewhere. What they found is that if we could turn back the clock and "re-play" Earth's history, it is probable that many of the minerals formed and discovered in this alternate version of our planet would be different from those we know today.

而在此情況下，Hazen的團隊提出了問題：地球礦物的分佈以及多樣性是如何形成？在其他地方有可能看到相同例子嗎？他們發現若我們將時間倒轉，並讓地球歷史重演，在這另一版本的地球上，我們很有可能會發現於此形成的礦物會與我們現今所認識的大相逕庭。

"This means that despite the physical, chemical, and biological factors that control most of our planet's mineral diversity, Earth's mineralogy is unique in the cosmos," Hazen said.

「這表示儘管物理、化學、生物法則控制了地球礦物的豐富程度，地球的礦物種類在宇宙中還是與眾不同的。」Hazen說。

The four papers are published in Canadian Mineralogist, Mathematical Geoscience, American Mineralogist, and Earth and Planetary Science Letters.

這四篇論文分別發表在《加拿大礦物學家》、《數學地球科學》、《美國礦物學家》、《地球與行星科學通訊》。

引用自：Carnegie Institution. "Earth's mineralogy unique in the cosmos." ScienceDaily. ScienceDaily, 26 August 2015.