科學家正逐步找出可以標記人類世的「金色之釘」
包括萊斯特大學地理、地質暨環境學院的地質學家Jan Zalasiewicz、Mark
Williams 和Colin Waters，以及考古學家Matt Edgeworth的國際工作小組自2009年開始就在分析可以用來正名人類世的實例。有望成為地質年代表中新時代的人類世，最主要的特徵便是人類對地球的影響已經大到不容忽視。
團隊發現有許多類型的物理、化學和生物標記都可以成為人類世的特徵，其中在全世界都能見到的最明顯標記是核武試爆降下的落塵中的放射性核種訊號，以及燃燒化石燃料造成碳的化學性質發生變化――它們都在1950年代早期至中期開始呈現特別顯著的變化。
團隊跟幾名他們邀請的科學家合作之下，近期回顧了現有知識中可以找到上述和其他類型標記，明確度、清晰度以及穩定性最高的訊號所在地層。或許可以運用它們來將人類世正式定義為地質年代表上的單位。
團隊最近的研究刊登於期刊《Earth-Science Reviews》，內容為向科學界表達他們會從哪些方面開始著手收集並分析有連續紀錄的岩芯樣本。這些岩芯涵蓋的地層會跨越他們提議的全新世和人類世之間的交界。
對於是否需要一個在世界各地，只要條件適合就有機會出現在不同環境中的「金色之釘」(golden spike)來定義人類世，有許多反對及支持的意見。研究剖析各種意見之後，發現人類世的地層雖然通常都很薄，但在世界各地皆有分布而可以被地質學家清楚辨識出來。
主持這項研究的Colin Waters表示：「在地質年代表上目前被認可的65根『金色之釘』都是位在沉積於海床的地層當中。唯一例外便是定義全新世起始時間的標記是位在冰芯當中。」
「這項研究仔細探究了那些可以良好紀錄人類世十分短暫歷史的環境。除了傳統地質學所用的地層之外，我們也考慮了人類製造的沉積物、累積在湖床的沉積物、河口、三角洲、泥炭沼、沉積在洞穴的礦物，甚至還有生物體，像是珊瑚和樹木。這些環境和生物當中許多都是一年堆積一層沉積物或形成一道生成紋，不管人類世基準的主要標記最後選擇在哪，這些環境和生物都在地質學上提供了絕無僅有的精準度來讓我們決定標記的所在位置。」
Jan
Zalasiewicz教授表示：「這項對世界各地『金色之釘』的候選地點進行的初步評估相當重要，它清楚顯示我們的選擇實在太多而難以決定――許多候選地點的標記都可以有效定義人類世。現在，我們前方還有許多工作要進行，我們必須仔細檢視最有潛力的幾個地點，看它們是否有足夠的細節可以將人類世的起始位置給真正固定下來，而且在全世界都可以被清楚並精準地辨識出來。」
Mark
Williams教授表示：「我們探討的環境種類相當多樣――從極地的冰雪到深不見底的湖泊、海床、珊瑚礁的骨骼以及洞穴裡的石筍。人類世的訊號在這些事物中都清晰可見的事實，顯示在二次大戰後人類的影響已經遍及地球的每個角落。」
人類世工作小組的科學家正致力於規劃一份提案，其根據是要先找到一根「金色之釘」，技術上來說是叫做全球界線層型剖面和點位(Global Boundary Stratotype Section and Point, GSSP)
這意味著研究人員將提出世上某個最近形成的地層，其中有條基準線可以將這道變化最為清楚一致地劃分出來：代表地球地質歷史最近11700年的全新世已經轉變成從65年前左右開始的人類世。
要讓此名詞被數個不同的地質組織正式認可的過程必須得花上未來數年的時間。一旦細節工作完成，提案會先呈交給國際地層學委員會之下的第四紀地層學小組來嚴格審查，但無法百分之百保證提案會被接受。
Scientists home in on a potential Anthropocene 'Golden Spike'
The international working group, which includes geologists Jan
Zalasiewicz, Mark Williams and Colin Waters, from the University of Leicester’s
School of Geography, Geology and the Environment and archaeologist Matt
Edgeworth has, since 2009, been analysing the case for formalisation of the
Anthropocene, a potential new epoch of geological time dominated by
overwhelming human impact on the Earth.
The group
has found that a broad range of potential physical, chemical and biological
markers characterise the Anthropocene, the clearest global markers being
radionuclide fallout signals from nuclear testing and changes in carbon
chemistry through fossil fuel burning – these in particular show marked changes
starting in the early to mid-1950s.
The group,
with a number of invited scientists, has now reviewed present knowledge on
where these and other markers form the clearest, sharpest, and most stable
signal in strata that might be used to define the Anthropocene as a formal unit
of the Geological Time Scale.
The
current study, which is published in the journal Earth-Science Reviews,
informs the scientific community where they should start the process of
collecting and analysing continuous core samples of strata across the proposed
Holocene–Anthropocene transition.
The study
considered a range of arguments in support of and against hosting a ‘golden
spike’ in a range of potentially suitable environments across the globe. They
found that Anthropocene strata are often thin – but also that they are globally
distributed and may be clearly recognised by geologists.
Professor
Colin Waters, who led the study, said: “Of the 65 ‘golden spikes’ of the
Geological Time Scale currently ratified, all but one are located in strata
that accumulated on the sea floor, the one exception being the ice core used to
define the base of the Holocene Epoch.
“This
study considers those environments in which the very short history of the
Anthropocene is best recorded. In addition to such traditional geological
strata, we have also considered human-generated deposits, sediments
accumulating in lakes, estuaries and deltas, peat bogs, cave mineral deposits
and even biological hosts such as corals and trees. The presence of annual
layers or growth rings within many of these provides geologically unprecedented
accuracy in the placement of the primary reference marker, wherever this might
be ultimately chosen.”
Professor
Jan Zalasiewicz said: “This preliminary assessment of potential ‘golden spike’
locations around the world is important in that it clearly shows we are spoilt
for choice – there are very many possibilities where the Anthropocene might be
effectively defined. Now we have a lot of work in front of us in examining the
most promising locations in enough detail to really pin down how the
Anthropocene might be clearly and precisely recognised around the world.”
Professor
Mark Williams said: “The range of environments we are working with is
remarkable – from polar ice and snow layers to deep lake and sea floors to the
skeletons of reef corals and stalactites in caves. The fact that signals of the
Anthropocene are so sharply visible in all of these shows just how pervasive
human impact has been on the planet in post-war times.”
Scientists
within the Anthropocene Working Group are working towards developing a
proposal, based upon finding a ‘golden spike’, more technically known as a
Global Boundary Stratotype Section and Point (GSSP).
This is a
reference level within recent strata somewhere in the world that will be
proposed to most clearly and consistently characterise the changes as the
Holocene, which represents the last 11,700 years of geological time on this
planet, gave way into the Anthropocene about 65 years ago.
Once this
detailed work is completed in a few years’ time — a required part of the
process in seeking formalisation of the term by a number of geological bodies
— it will first be submitted for scrutiny to the Subcommission on
Quaternary Stratigraphy of the International Commission on Stratigraphy. There
is no guarantee, though, that the proposal will be accepted.
原始論文：Colin N.
Waters, Jan Zalasiewicz, Colin Summerhayes, Ian J. Fairchild, Neil L. Rose,
Neil J. Loader, William Shotyk, Alejandro Cearreta, Martin J. Head, James P.M.
Syvitski, Mark Williams, Michael Wagreich, Anthony D. Barnosky, An Zhisheng,
Reinhold Leinfelder, Catherine Jeandel, Agnieszka Gałuszka, Juliana A. Ivar do
Sul, Felix Gradstein, Will Steffen, John R. McNeill, Scott Wing, Clément
Poirier, Matt Edgeworth. Global Boundary Stratotype Section and Point
(GSSP) for the Anthropocene Series: Where and how to look for potential
candidates. Earth-Science Reviews, 2017; DOI: 10.1016/j.earscirev.2017.12.016
引用自：University of Leicester. "Scientists home
in on a potential Anthropocene 'Golden Spike'."
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