科學(xué)家最近又有新的研究成果：來(lái)自加拿大北部古老巖石樣品中的碳物質(zhì)的年齡比之前所認(rèn)為的“年輕”數(shù)百萬(wàn)年,。
圖： 來(lái)自波士頓大學(xué)的Papineau教授
該研究小組的成員包括來(lái)自美國(guó)波士頓大學(xué)（Boston College）,，華盛頓卡內(nèi)基研究所（Carnegie Institution of Washington）,，美國(guó)航天局約翰遜航天中心（NASA's Johnson Space Center）和海軍研究實(shí)驗(yàn)室（Naval Research Laboratory）多領(lǐng)域的科學(xué)家,，新的研究證據(jù)顯示,，加拿大哈德遜灣地區(qū)（Canada's Hudson Bay）的碳顆粒并不是與巖石的形成年代一致,，這中間有數(shù)百萬(wàn)年的差距,。
樣品來(lái)自于太古代（Archean）蘇必利爾克拉通地區(qū)（Superior craton）的條帶狀鐵建造（BIF）,。為了更確切的認(rèn)識(shí)巖石中所保存的碳物質(zhì)信息,，科學(xué)家們利用一系列的高科技檢測(cè)手段。傳統(tǒng)的做法會(huì)將采集的樣品研碎磨成粉,，然后對(duì)碳質(zhì)進(jìn)行分析研究,。新的研究方法則利用顯微鏡和光譜學(xué)方法直接從巖石樣品中分析研究石墨結(jié)晶的原始完整微結(jié)構(gòu)。研究結(jié)果顯示這些碳質(zhì)相比其圍巖的年齡要晚上很多,。
波士頓大學(xué)科學(xué)家D. Papineau介紹說(shuō)：“這些石墨結(jié)晶的特征與巖石的變質(zhì)歷史并不一致,，表明石墨中碳的形成年代并沒有巖石的年代古老。這給我們敲響了警鐘,，以前的研究結(jié)果需要我們重新審視了,。”
Papineau還說(shuō)道：“格陵蘭距今約40億年的樣品被認(rèn)為是最早生命出現(xiàn)的證據(jù)。但新的研究結(jié)果表明最早生命出現(xiàn)的時(shí)間要往后推數(shù)百萬(wàn)年，而且仍需更嚴(yán)謹(jǐn)深入的研究,?？茖W(xué)家們現(xiàn)在要回去格陵蘭重新確定這些碳物質(zhì)是否與這些變質(zhì)巖的年齡一樣古老了！”
隨著地球的演化,，巖石和其它物質(zhì)都會(huì)受到一系列高溫高壓的影響,，古老的巖石絕大多數(shù)會(huì)遭受這樣高變質(zhì)作用影響。早期地球的碳物質(zhì)主要來(lái)自于早期的微生物,，它是早期生命存在的主要信息來(lái)源之一,，是地球演化歷史重要的里程碑。
Papineau最后補(bǔ)充道：“現(xiàn)在我們的建議是：在最古老的變質(zhì)巖中,，碳物質(zhì)可能并不是本來(lái)就有的,，在研究這些時(shí)代非常古老的巖石時(shí)，需要解決的兩個(gè)根本問(wèn)題是碳質(zhì)是否來(lái)源于生物,，以及其與巖石是否是同一時(shí)間形成保存至今的,。”（生物谷Bioon.com）
生物谷推薦原文出處：
Geochimica et Cosmochimica Acta doi:10.1016/j.gca.2010.05.025
Ancient graphite in the Eoarchean quartz–pyroxene rocks from Akilia in southern West Greenland I: Petrographic and spectroscopic characterization
Dominic Papineau , Bradley T. De Gregorio, George D. Cody, Marc D. Fries, Stephen J. Mojzsis, Andrew Steele, Rhonda M. Stroudb and Marilyn L. Fogel
Because all known Eoarchean (>3.65 Ga) volcano-sedimentary terranes are locked in granitoid gneiss complexes that have experienced high degrees of metamorphism and deformation, the origin and mode of preservation of carbonaceous material in the oldest metasedimentary rocks remain a subject of vigorous debate. To determine the biogenicity of carbon in graphite in such rocks, carbonaceous material must be demonstrably indigenous and its composition should be consistent with thermally altered biogenic carbon as well as inconsistent with abiogenic carbon. Here we report the petrological and spectroscopic characteristics of carbonaceous material, typically associated with individual apatite grains, but also with various other minerals including calcite, in a >3.83 Ga granulite-facies ferruginous quartz-pyroxene unit (Qp rock) from the island of Akilia in southern West Greenland. In thin sections of the fine-grained parts of Akilia Qp rock sample G91-26, mapped apatites were found to be associated with graphite in about 20% of the occurrences. Raman spectra of this carbonaceous material had strong G-band and small D-band absorptions indicative of crystalline graphite. Three apatite-associated graphites were found to contain curled graphite structures, identified by an anomalously intense second-order D-band (or 2D-band) Raman mode. These structures are similar to graphite whiskers or cones documented to form at high temperatures. Raman spectra of apatite-associated graphite were consistent with formation at temperatures calculated to be between 635 and 830 °C, which are consistent with granulite-facies metamorphic conditions. Three graphite targets extracted by focused ion beam (FIB) methods contained thin graphite coatings on apatite grains rather than inclusions sensu stricto as inferred from transmitted light microscopy and Raman spectroscopy. TEM analyses of graphite in these FIB sections showed a (0 0 0 2) interplanar spacing between 3.41 and 3.64 ? for apatite-associated graphite, which is larger than the spacing of pure graphite (3.35 ?) and may be caused by the presence of non-carbon heteroatoms in interlayer sites. Samples analyzed by synchrotron-based scanning transmission X-ray microscopy (STXM) also confirmed the presence of crystalline graphite, but abundances of N and O heteroatoms were below detection limit for this method. Graphite in the Akilia Qp rock was also found to occur in complex polyphase mineral assemblages of hornblende ± calcite ± sulfides ± magnetite that point to high-temperature precipitation from carbon-bearing fluids. These complex mineral assemblages may represent another generation of graphitization that could have occurred during the amphibolite-facies metamorphic event at 2.7 Ga. Several observations point to graphitization from high-temperature fluid-deposition for some of the Akilia graphite and our results do not exclude a biogenic source of carbon in graphite associated with apatite, but ambiguities remain for the origin of this carbon.
