Stephen Meyer's book Signature in the Cell is primarily devoted to assessing attempts by materialists to explain the origin of information in life. Over the course of about four pages, he includes a short discussion of a peripherally related topic, the earth's early atmosphere and the likelihood of chemical monomers forming on the early earth. He notes that "[i]n the years following Miller's experiment, however, new geochemical evidence showed that the assumptions Miller had made about the early atmosphere were incorrect" and that a "neutral" atmosphere which is "not friendly to the production of amino acids" is more likely." (pp. 224-225) Some critics have claimed that recent research shows that that the Earth's early atmosphere was in fact reducing, and that Meyer's claims do not hold up. Are the critics right?
One critic who has made such arguments is Gary Hurd, an anti-ID blogger with a Ph.D. in anthropology, who in a recent Amazon review argues that Stephen Meyer's book Signature in the Cell is "outdated" because Meyer contends that the earth's early atmosphere was not reducing, and, therefore, would not have readily produced the amino acids needed for life. Hurd also charges that Meyer's book is the result of "self-plagiarism."
A closer examination shows that Hurd's review is an exercise in citation-bluffing.
His charge that Meyer is guilty of self-plagiarism is both absurd and inaccurate. Further, a fair-minded examination of the most recent evidence shows that Meyer's assessment of the earth's early atmosphere is not outdated at all. Instead, Hurd's claim that geochemical evidence supports a reducing atmosphere capable of generating amino acids is both out-of-date and inaccurate. Moreover, none of the papers that Hurd cites respond to Meyer's central thesis that intelligence design best explains the functionally specified information necessary to produce the first living cells. Indeed, even if Hurd were correct in asserting that the early earth's atmosphere could readily produce amino acids, that would not explain how amino acids arranged themselves into functional proteins, nor would it explain the origin of the sequence specificity (information) present in DNA and RNA.
Hurd cites nine papers to show that Meyer's discussion of the composition of the earth's pre-biotic atmosphere "is outdated." Yet there are good reasons that Meyer did not cite these papers: six fail even to discuss the composition of the earth's prebiotic atmosphere (contrary to Hurd's claim); two make highly controversial claims contradicted by leading authorities in more recent publications; and one confirms two key claims that Meyer himself had already made (and carefully documented) in Signature.
What follows is a brief survey of the papers cited by Hurd:
6 papers were citation bluffs:
4 papers focus on the earth's post-biotic atmosphere (i.e. the atmosphere after life already existed on earth) and were irrelevant to investigating the nature of earth's atmosphere prior to the origin of life. (Catling et al. 2002, Kasting and Siefert 2002, Pavlov et al. 2001, Wolf and Toon 2010.) Another paper discusses the impact of meteorites on the earth's early atmosphere but did not discuss the composition of the earth's prebiotic atmosphere or the formation of prebiotic monomers. (Genda and Abe 2003.) Another paper discusses the formation of ribose, not the earth's early atmosphere. (Ricardo et al. 2004.)
Of the three remaining papers, two discuss the early earth's atmosphere but come to conclusions that have been contradicted by more recent and authoritative studies. One reports a simulation experiment that confirms rather than challenges key points made in Signature in the Cell:
Holland (1999) discusses ancient rocks thought to have been chemically influenced by the earth's early atmosphere. Hurd doesn't reveal that this evidence is highly controversial and subject to conflicting interpretations since the rocks Holland examines have undergone many changes in their 3+ billion year history and since depositional environments are often difficult to ascertain. Moreover, Holland's paper is now outdated in light of more recent publications by his opponents, such as Ohmoto (2006 & 2009), who think the rock record shows earth's early atmosphere was not reducing. Tian et al. (2005)'s conclusion that the earth's early atmosphere was high in hydrogen (and therefore reducing) has been called into question by multiple leading authorities--including Catling, Kasting, Bada, Lazcano, and even Stanley Miller--who have, among other things, challenged the paper's calculations. Cleaves et al. (2008) claims amino acids could have been produced in a neutral atmosphere, but the simulation experiment that they performed to demonstrate this conclusion required extensive intelligent intervention. Cleaves et al. added a buffer, oxidizing inhibitors, and acid hydrolysis "to convert any precursors to amino acids." By 'seasoning' their prebiotic soup, they intentionally created an artificially reducing environment. Thus, their simulation experiment neither documents the existence of a reducing atmosphere nor the capacity of a neutral atmosphere to generate monomers without intelligent intervention. As Meyer has pointed out, such experiments "simulate, if they simulated anything, the power of, and arguably the need for, intelligence" to move chemistry in a life-friendly direction. Ironically, the CO2-N2-H2O atmosphere used by this 2008 paper is the precise atmosphere Meyer reports was present on the early earth, showing that Meyer's view of this issue is anything but outdated.
Of course, one might still fault Meyer for failing to cite these papers, but given that at least six of these papers were completely irrelevant to analyzing the earth's pre-biotic atmosphere, and two have been contradicted by more recent authorities, Hurd's broadside against Meyer's scholarship reduces to the claim that he failed to cite one paper (Cleaves et. al.) that actually reinforced claims that Meyer had already amply documented. This hardly constitutes a breach of scholarly rigor.
Hurd also asserts that Meyer plagiarized himself (as if that were possible). But scientists and scholars regularly produce longer books and monographs by expanding on previously published shorter articles. He also claims that Meyer has done no new research since 1998. But this is clearly false. Signature in the Cell contains hundreds of post-1998 citations. Moreover, Meyer's article to which Hurd objects, and which admittedly served as source material for parts of his greatly expanded book, graced only 38 published pages, whereas Signature runs over 600. Clearly, the book contains a great deal of novel material. Granted, it contains little new in its assessment of the pre-biotic atmosphere. But for good reason. Leading experts on the early earth's atmosphere continue to doubt that the atmosphere was reducing. The articles that Hurd cites do not show otherwise.
Were it not that Hurd is a Ph.D. scientist and a well-known anti-ID blogger who writes as if he possessed authoritative expertise about the early earth's atmosphere, his citation-bluffing would not warrant a response. But since his review appears authoritative but is actually highly misleading, I have chosen to respond here.
In conclusion: Not only do Hurd's citations fail to establish a pre-biotic atmosphere, they do nothing to refute Meyer's main argument about the origin of biological information. If this is the best critique of Meyer's argument that prominent ID-critics can muster, then I think Meyer can rest easy that his thesis is strong. The argument in Signature in the Cell remains every bit the "game changer" that previous Amazon reviewers have said.
Part II: Citation Bluffing in Hurd's Amazon Review
Proponents of undirected evolution have long employed a strategy to overcome weaknesses in their arguments. This strategy preys on those who are overly impressed or intimidated by citations to technical scientific papers. It's called citation (or literature) bluffing, and the tactic goes something like this:
First, make a controversial claim in favor of evolution. Then list a bunch of impressive-sounding technical papers that appear to support that claim. Do not quote from or describe the contents of the papers. That wouldn't be a bluff, because it would require actually dealing with the evidence. Instead, just enumerate the references in laundry-list fashion, as if they all supported the point. Count on no one taking the time to dig up the obscure references and fact-check the claims. (Subscription-required journal access often makes it nearly impossible for readers to fact-check anyway.) Otherwise, readers would discover the papers are either irrelevant to the claim being made or contradict one another and don't support a coherent argument. If the bluff works, those who place unjustified faith in the infallibility of the peer-review process will be impressed, gloating that the juggernaut of science has rolled over the skeptics. Meanwhile, the mass of people who aren't familiar with the technical literature--or don't have access to it--will be intimidated from further comment.
Pandas Thumb blogger Gary Hurd's recent review of Stephen Meyer's book Signature in the Cell on Amazon.com was titled "Obsolete, Misleading Cut n' Paste."1 The review is an exercise in citation bluffing. Before we analyze the bluffs in detail, let's start with Hurd's other claims.
Since When is Reworking Your Own Material a Crime?
From the first words of his review, it's clear that Hurd is stretching for reasons to attack Stephen Meyer. Hurd complains that that on about four pages of Signature in the Cell "we have a cut n' paste with only trivial alterations from an [sic] 1998 article Meyer wrote, 'DNA by Design'."
Anyone who has read the 600+ page Signature in the Cell and is familiar with Meyer's prior work is immediately aware of two things: (1) Signature in the Cell discusses topics Meyer has written about in the past (no surprise!)--just in much more depth, and (2) The added depth in Signature in the Cell means that there is a LOT of new material in the book. In fact, Meyer's "DNA by Design" runs to only 38 pages, whereas Signature in the Cell contains over 600 pages. Obviously Signature includes a lot of new material.
The fact is, there's nothing wrong with drawing on one's prior work, something scientists, not to mention scholars in other fields, do all the time.
Hurd's Outdated Arguments
Hurd's next attempt at rebuttal fares even worse. He claims Meyer hasn't updated arguments since 1998, when Meyer published "DNA by Design." Hurd complains:
Text from 'DNA by Design' appears quite often in 'Signature.' The most irritating feature is that in ten years between that early text and 'Signature,' Meyer had not even bothered to update critical references, let along his outdated thinking.
This charge is bizarre since a quick perusal of Signature in the Cell's bibliography shows many--far more than 200 in fact--of Meyer's citations were published after 1998. If Hurd wishes to cast Meyer as having dropped out of researching this issue in 1998, he's going to have to explain the hundreds of citations in Signature showing otherwise.
Hurd inaccurately dates Meyer's book to 2010, but Signature was published in 2009, which makes it all the more impressive that Signature cites a number of scientific papers from 2008, just before the book was published.
Clearly Signature in the Cell is not generally outdated, and contrary to Hurd's claim, Meyer did not stop researching this issue in 1998. But Hurd specifically attempts to target the "outdated thinking" charge to Meyer's discussion of the composition of the Earth's prebiotic atmosphere. Thus, we must ask the question, is Meyer's treatment of the Earth's prebiotic atmosphere in Signature in the Cell inaccurate and outdated?
Part III: The Big Picture and the Lack of an Information Generating Mechanism
Before delving into Hurd's central thesis we must remind ourselves of the big picture here. Even if Hurd's critique were valid, it would only explain how chemical monomers might have arisen on the prebiotic earth. But Meyer's argument in Signature in the Cell goes much further and contends that there is no natural explanation for the origin of biological information in DNA. Meyer devotes only a few pages to the prebiotic soup in Signature because, even granted a prebiotic soup, the origin of biological information stands unexplained.
A simple analogy helps explain the paucity of evidence for a naturalistic origin of the information in life. Living cells function due to the information they contain. If a living cell is like a book, then amino acids are analogous to letters. At best, the prebiotic soup hypothesis explains how to produce letters.
As anyone who has lost a game of Scrabble is painfully aware, you can have all the letters you want, but without the ability to organize them into meaningful information, they will forever remain nothing more than disorganized Scrabble letters. Without intelligence, they will never organize themselves into sentences, paragraphs, chapters, or any other form of meaningful information.
Given that amino acids will not chemically link into proteins chains in an aqueous environment (like the prebiotic soup),2 it's difficult to understand how words and sentences (larger biomolecules like peptides) could even form out of the letters (amino acids and other monomers) under our analogy.
The prebiotic soup hypothesis doesn't hold much water, no pun intended. The poor state of affairs for origin of life researchers is exposed when they have such great difficulty explaining how the "letters" arose, but their ultimate task is to explain how a book arose via unguided and blind natural processes.
However, I will show below, Hurd has not made his case that Meyer's treatment of the prebiotic soup is inaccurate.
Part IV: Testing Hurd's Central Thesis
Hurd's main thesis includes the following:
What did Meyer use this group of citations to support? That the late-Hadean, early-Archean had an oxygenated atmosphere... Meyer, in 1998, might have been justified in thinking that scientific opinion was divided among geochemists regarding the Earth's early redox state. After all he is not really a geologist, nor a chemist. But, even though his under-graduate geology degree was from a religious school, his continued ignorance was not justified in 2008-2009.
Hurd argues that geochemists are no longer divided on the redox state of the Earth's early atmosphere, and that they believe it was reducing. Let's look specifically at what Meyer says:
Yet when Stanley Miller conducted his experiment simulating the production of amino acids on the early earth, he had presupposed that the earth's atmosphere was composed of a mixture of what chemists call reducing gases, such as methane (CH4), ammonia (NH3), and hydrogen (H2). He also assumed that the earth's early atmosphere contained virtually no free oxygen. In the years following Miller's experiment, however, new geochemical evidence showed that the assumptions Miller had made were incorrect. Instead, evidence strongly suggested that neutral gases such as carbon dioxide, nitrogen, and water vapor--not methane, ammonia, and hydrogen--predominated in the early atmosphere. Moreover, a number of geochemical studies showed that significant amounts of free oxygen were present ... probably as the result of photo-disassociation of water vapor.3
Ignoring Hurd's weird attacks upon Meyer's education (I'll discuss these strange comments at the end), Hurd apparently does not know that as recently as 2008, in a paper in Science, Jeffrey Bada and other experts made a statement that sounds much like Meyer's claim:
Geoscientists today doubt that the primitive atmosphere had the highly reducing composition Miller used...4
The 2008 paper quoted above directly contradicts Hurd's assertion that "[p]ublications, several by the very people Meyer has cited, since 1998 have conclusively made the case for a late-Hadean / early-Archean reduced atmosphere...". (The paper also speculates about the possibility of reducing oases, an idea Hurd also raises, which I'll discuss at the end of this response.)
And contra Hurd, other recent authorities have argued that the redox state of the early Earth was the same as it is today. In February 2010, NPR reported that biochemist Nick Lane believes that the priomordial soup theory is "past its expiration date."5 Likewise, a 2010 paper in Cold Spring Harbor Perspectives in Biology states:
Geochemical evidence in Earth's oldest igneous rocks indicates that the redox state of the Earth's mantle has not changed over the past 3.8 Gyr (Delano 2001; Canil 2002).6
The papers cited in the quote above confirm this point. For example, Canil's 2002 paper in Earth and Planetary Science Letters found that vanadium redox states in peridotite-bearing mantle xenoliths and Archean cratons imply that Earth's mantle was just as oxidized in the Archean as it is today. The paper concludes:
Abiotic synthesis of molecules and hydrocarbons that can lead to life in early Archean mantle-derived volcanic gases requires they contain significant H2 and CO, but such reduced components are not supported by results of this and many other studies, which imply a scenario of Archean mantle redox not unlike that of today. Life may have found its origins in other environments or by other mechanisms.7
The situation is summed by Kasting and Catling as follows: "For the 4 billion years for which a geological record exists, no evidence for a pronounced change in mantle redox state exists."8 These papers thus confirm what Meyer argued in 1998: the atmosphere on the early Earth was not generally reducing.
Hurd claims that scientific opinion about Earth's early redox state is not divided. If that's the case, then it would seem that geochemists believe the early Earth's redox state was similar to its present redox state and did not produce a reducing atmosphere. This contradicts Hurd's claim, but it supports Meyer's claims in Signature in the Cell, showing Meyer's discussion is not "outdated" on this point.
Part V: Assessing Hurd's Citation Bluffs
Hurd goes on to claim that the non-reducing nature of the Earth's early atmosphere is readily discussed in post-1998 research, stating:
Even articles readily available prior to 2008 make this obvious, and subsequent research has 'capped' the argument.
Then, Hurd begins his literature bluff. It consists of nine articles, six of which turn out to be bluffs--more or less irrelevant to the question at hand. The other three are highly inconclusive and controversial, showing that, at best, opinion in this field is divided. Each of the nine articles cited by Hurd will now be assessed.
Citation #1: Literature Bluff: Catling, David C., Kevin J. Zahnle, Christopher P. McKay 2002 "Reply to Towe (2002)" Science letters v.295 (5559):1419a
Response: This paper debates the Earth's atmosphere, specifically its methane content, long after the origin of life, asserting there could have been methane on the early Earth "given a plausible biogenic source." It's addressing a different topic from the Earth's atmosphere at the time of the origin of life and is thus irrelevant to a discussion of the prebiotic atmosphere. This paper is a citation bluff: it is not relevant to the point Hurd is trying to establish regarding the Earth's atmosphere before life originated.
Citation #2: Literature Bluff: Genda, Hidenori & Abe, Yutaka 2003 "Survival of a proto-atmosphere through the stage of giant impacts: the mechanical aspects" Icarus 164, 149-162 (2003).
Response: This paper is another literature bluff. It argues that a planet's atmosphere might not be lost during a meteorite impact, but it doesn't say anything about the actual composition of the Earth's early atmosphere.
Citation #3: Literature Bluff: J. F. Kasting, J. L. Siefert, 2002 "Life and the Evolution of Earth's Atmosphere" Science 296:1066
Response: Much like bluff # 1, this paper discusses the Earth's atmosphere after life arose, so it's not much help in assessing the prebiotic atmosphere. It's a fascinating paper, but it's discussing the wrong topic.
Citation #4: Literature Bluff: Pavlov, Alexander, James K. Kasting, Jeninifer L. Eigenbrode, Katherine H. Freeman 2001 "Organic haze in Earth's early atmosphere: Source of low-13C Late Archean kerogens?" Geology v.29 no. 11:1003-1006
Response: Once again, this is a fascinating paper, but it's about how methanogenic bacteria could have changed Earth's atmosphere after life was prevalent on Earth. It addresses the Earth's atmosphere post-origin of life, not the atmosphere prior to life's origin and is irrelevant to the point Hurd is claiming to establish. It therefore is a citation bluff.
Citation #5: Literature Bluff: Ricardo, A., Carrigan, M. A., Olcott, A. N., Benner, S. A. 2004 "Borate Minerals Stabilize Ribose" Science January 9; 303: 196 (in Brevia)
Response: This paper has absolutely nothing to do with the Earth's atmosphere. It discusses a complicated pathway for forming ribose, a point has essentially nothing to do with Hurd's charges against Meyer.
As a side-note, this paper leaves off an important point: it notes that while the processes used in the experiment did produce ribose, they also produced a variety of other sugars: "The presence of arabinose, lyxose, xylose, and ribose in similar amounts was confirmed."9 However, as Kasting and Catling explain, this does not solve the problem of producing ribose in a manner that is useful for forming life: "Polymerizing [precursors of sugars] in such a way as to produce predominately ribose, as opposed to other sugars, is a difficult task. We shall assume, however, that nature figured out how to accomplish this."10
Citation #6: Literature Bluff: E. T. Wolf and O. B. Toon 2010 "Fractal Organic Hazes Provided an Ultraviolet Shield for Early Earth" Science 4 June 328: 1266-1268 [DOI: 10.1126/science.1183260] (in Reports).
Response: This paper does discuss the Earth's pre-biotic atmosphere. However, doesn't provide any new evidence concerning the Earth's early atmosphere. In fact it simply assumes that the early Earth's atmosphere had significant amounts of methane and was almost entirely nitrogen-based--a view that is outside the consensus view today. JPL scientist Michael John Russell notes this very point in rebuttal to this paper:
E. T. Wolf and O. B. Toon base their fractal haze theory on the assumption that the Archean atmosphere was primarily N2. The Report includes no reference for this 'prevailing view,' and much evidence can be amassed against it. Geologists since Darwin have uniformly argued for a CO2-dominant atmosphere for the early Earth.11
In fact, when responding to Russell, Wolf and Toon state: "Admittedly, achieving high methane concentrations before organic material existed on Earth is difficult," and thus they base their hypothesis primarily upon methane "supplied by methanogens are predicted for the postbiotic Earth."12 Thus at best, like many other papers cited by Hurd, their ideas apply after the origin of life--on the "postbiotic Earth."
Notably, Wolf and Toon admit their model is highly dependent on the redox state of the early Earth's mantle: "The degree to which the Archean atmosphere was reducing is dependent on the redox state of the young mantle, which is not well constrained but is believed to have been more reduced than today."13 Their justification cites to a paper in 1993, but as we have seen above, more recent research suggests that the early Earth's mantle's redox state was the same as it is today--non-reducing. Thus, I include this paper as a literature bluff because it contains no independent evidence of the Earth's atmosphere, just a model of the atmosphere assuming that it contained methane, and also because its authors admit their model best applies to the "postbiotic Earth."
We've now assessed six of the nine papers cited by Gary Hurd, and found that they are either irrelevant or do not establish the point he was trying to make. They are citation bluffs. Now we'll assess some slightly on-point papers.
Part VI: Hurd's Two Slightly On Point Papers
Two papers Hurd cites were slightly relevant. However, they are highly inconclusive and contradicted by later papers and research. They counter Hurd's claim that scientists are not "divided" regarding the early Earth's redox state, and defeat his charge that Meyer's arguments are "outdated."
Citation #7: Slightly On Point: Holland, Heinrich D. 1999 "When did the Earth's atmosphere become oxic? A Reply." The Geochemical News #100: 20-22
Comment: This 1999 paper cited by Hurd is a reply from Heinrich Holland to Hiroshi Ohmoto, a researcher Penn State, who is a leader in the field of paleoatmospheric studies. Though in the minority, Ohmoto argues that the early Earth's atmosphere contained appreciable amounts of oxygen. Holland disagrees, hence this paper.
Much of Holland's reply to Ohmoto assesses evidence in the postbiotic Earth, and might not directly shed light on the Earth's prebiotic atmosphere. So this paper cited by Hurd is not entirely on-point--but it's worth investigating nonetheless since Ohmoto argues that oxygen was prevalent in the earth's atmosphere as early as 3.8 Ga, a relevant question.
This particular debate between Holland and Ohmoto treads into controversial territory because it attempts to infer the Earth's ancient atmosphere based upon chemical properties of rocks that are billions of years old. The general difficulty with this approach is that Archean rocks have undergone many changes in the 2.5+ billion years since they were originally deposited, not all of which are related to atmospheric interactions. It's difficult to demonstrate that these ancient rocks bear features resulting from interaction with the early atmosphere, and not other processes occurring at that ancient time, or during much later periods. What is more, the evidence in this debate is often contradictory: rocks of the same time period can point in opposite directions regarding the composition of the atmosphere.
Holland's article acknowledges the inconclusive nature of these data, as he writes in one case: "Their data do not settle the matter conclusively, since other interpretations are equally reasonable."14 Another authority, James Kasting, similarly wrote in 2001 regarding this debate that, "some geologists remained skeptical because the geochemical and biological data allowed room for alternative interpretations."15 Again in 2006 Kasting wrote "the geological evidence for this is indirect and subject to interpretation," further noting "[t]he jury is still out" due to "contradictory observations."16
Even more revealing are the writings of Ohmoto's protégé, Kosei Yamaguchi, now at the NASA Astrobiology Institute. In 2005, Yamaguchi wrote that "The timing of the rise of O2 in the ancient atmosphere has been vigorously debated since 1950, and no firm consensus has been reached ... because of [the evidence's] indirect nature, much of it is circumstantial and all of it is no better than semi-quantitative."17 Notably, Yamaguchi's review paper catalogues 11 lines of evidence pointing to low (or no) oxygen in the early atmosphere, but 16 pointing to high oxygen.18 Even more importantly, Yamaguchi cites over 20 scientific papers published since Holland's 1999 paper (the one Hurd cites) which discuss geological discoveries suggesting a high O2 in the early Earth's atmosphere.
This paper cited by Hurd is itself somewhat outdated, and Hurd fails to mention more recent evidence cited by Yamaguchi. Nor does Hurd mention various recent papers by Holland's opponent, Ohmoto arguing for oxygen in the Earth's ancient atmosphere. In 2006, Ohmoto published research in Nature suggesting oxygen may have been prevalent in the Earth's early atmosphere as far back as 3.8 billion years ago.19 Live Science reported on this research stating:
The new findings could mean oxygen levels on Earth were uniformly high since 3.8 billion years ago, Ohmoto said. They could also mean oxygen levels went through yo-yo fluctuations between highs and lows. ... "There is going to be a howl, even outrage," over these findings, geologist and isotope geochemist Paul Knauth at Arizona State University told LiveScience. They will say hot springs could have swamped the rocks Ohmoto and his colleagues looked at with normal sulfur, or that the crystals they analyzed washed in from elsewhere, or that their measurements are inaccurate, he said. However, Knauth noted Ohmoto and his colleagues did address these points "and make good arguments."20
Likewise, in 2009 Ohmoto published a paper in Science which showed that geochemical arguments against the existence of oxygen in the early atmosphere might have resulted from other processes.21
None of this more recent research--which shows how much the debate has evolved since Holland's 1999 paper--is cited by Hurd. But isn't that the charge Hurd levies against Meyer--that his discussion is outdated? Perhaps Hurd should just drop accusations that Meyer's discussion is outdated, lest his rebuttal become subject to the same charge.
To be sure, many experts still doubt that oxygen was prevalent in the Earth's early atmosphere, but there are also leading experts who believe oxygen was present in appreciable amounts. Opinion is divided on how to interpret geochemical signatures in ancient rocks. Hurd's citation of Holland's 1999 article regarding geochemical signatures in ancient rocks is extremely outdated as this debate has evolved significantly since that time. What isn't outdated, however, is that today, just as in 1998, there is sharp disagreement among scientists about the existence of oxygen in the early Earth.
If Hurd wants to play the "outdating" game with Meyer, he's going to lose. Consider why: Meyer's book doesn't even tread into the debate over geochemical signatures in ancient rocks. Rather, he made a theoretical argument that there might have been a chemically significant amount of oxygen in the Earth's early atmosphere due to photodissociation of water vapor. This is a strong theoretical argument supported by multiple authorities--an argument which is NOT addressed by Holland's paper. Rather, Holland only discusses inconclusive circumstantial evidence from the rock record.
In effect, Hurd's citation does not respond to Meyer's argument. While now-outdated Holland paper cited by Hurd undertakes the difficult task of inferring the Earth's early atmosphere from the rock record, it is irrelevant to rebutting Meyer's point.
If papers from 1999 are acceptable to Gary Hurd, then it's noteworthy that a paper published the same year as Holland's paper essentially validated Meyer's description of the atmosphere: "modern geochemistry assumes that the secondary atmosphere of the primitive Earth (i.e. after diffusion of hydrogen and helium into space) had been formed by outgassing of volcanoes and therefore that it mainly consisted of carbon dioxide, nitrogen, water, sulfur dioxide, and even small amounts of oxygen."22 In essence, Hurd offers no evidence that Meyer's actual argument--that oxygen from photodissociation might have existed in the earth's early atmosphere--is outdated or even wrong.
Citation #8: Somewhat On Point: Tian, Feng , Owen B. Toon, Alexander A. Pavlov, and H. De Sterck 2005 "A Hydrogen-Rich Early Earth Atmosphere" Science 13 May; 308: 1014-1017; published online 7 April 2005
Response: This paper claims that hydrogen on the early Earth might have been present in greater amounts than was previously thought, potentially allowing allow Miller-Urey type chemical reactions to occur, yielding amino acids. However, this paper has engendered a significant amount of controversy and criticism, and carries little weight at present. In fact, a different paper also cited by Hurd strongly contravenes Tian et al.'s claims, noting that H2 "would have been rapidly replaced by a more neutral atmosphere as H2 was lost to space":
However, it is now generally held that the early Earth's atmosphere was likely not reducing, but was dominated by N2 and CO2. ... It is generally agreed that there was little free oxygen in the early atmosphere, but opinions vary regarding the remainder of the primitive atmosphere's composition. Estimates range from reducing (CH2 + H2 + NH2 + H2O, or CO2 + H2 + N2) to neutral (CO2 + N2 + H2O). A weakly reducing or neutral atmosphere appears to be more in agreement with most current models for the early Earth. Although there may have been a short lived period early in Earth's history when the atmosphere was reducing due to accumulation of H2 derived from photodissociation of reduced volcanic species (Tian et al. 2005), this would have been rapidly replaced by a more neutral atmosphere as H2 was lost to space.23
Catling and Claire similarly critique Tian et al. as follows:
A recent paper [Tian et al.] suggests that the early atmosphere was highly reducing because of a slower rate of hydrogen escape to space than previously thought. However, this slow escape rate stems from questionable assumptions. [Tian et al.] only consider temperature-dependent hydrogen escape and assume a pure H2 upper atmosphere, which necessarily generates a cold exosphere because neither the absorption of extreme ultraviolet by other gases nor the higher temperature of atomic ions is considered. Also, non-thermal escape processes dominate today and cannot be dismissed for early Earth.24
The authority Kasting also urges caution when citing Tian et al. due to miscalculations in the paper's research:
Catling (2006) has questioned the new calculation, arguing that it is still over-simplified and the authors may have underestimated both the upper atmospheric temperatures and the hydrogen escape rates. Clearly, more work needs to be done to test whether the Tian et al. results are robust.25
In other words, Tian et al.'s 2005 model has failed to convince leaders in this field--including David Catling, James Kasting, Stanley Miller, Jeffrey Bada, and Antonio Lazcano--that H2 content was high in the Earth's early atmosphere. This controversial Tian et al. paper is directly contradicted by other papers--including papers cited by Hurd! Given the criticism levied at this paper, it does not deserve much credence from Meyer.
We now come to this final paper cited by Hurd, the one quoted above that contravened Tian et al.
Part VII: Amino Acids in a Neutral Atmosphere? Hurd's One Relevant Citation.
Thus far, we have seen that 8 of the 9 papers cited by Hurd are either irrelevant to this question, do not respond to Meyer, or do not support Hurd's critique of Meyer. Arguably, they are citation bluffs. However, part of Hurd's thesis also claims that there may have been "a neutral atmosphere with common, strongly reducing oasis."
The one remaining paper from Hurd does argue for a neutral atmosphere. This paper is Cleaves et al. (2008), co-authored by Stanley Miller and other origin of life authorities like Jeffrey Bada and Antonio Lazcano. Bada was one of my own professors in my undergraduate studies, and I also took at least one seminar lecture from Stanley Miller. This is a field which I am somewhat familiar with.
The problem for Hurd's attack on Signature in the Cell is that Stephen Meyer agrees with this paper that the Earth's early atmosphere was probably neutral, so this paper does not contravene Meyer's claims about the atmosphere. As noted earlier, Meyer wrote:
Instead, evidence strongly suggested that neutral gases such as carbon dioxide, nitrogen, and water vapor--not methane, ammonia, and hydrogen--predominated in the early atmosphere.26
This is in fact the precise atmosphere postulated by the final remaining citation from Hurd. It thus validates the very claim from Meyer which Hurd argues was wrong, with one twist: Hurd claims that the paper demonstrates that "prolific natural production of complex biomolecules can take place in neutral to even slightly oxic atmospheres." We'll assess this paper below and assess whether Hurd has overstated its findings.
Citation #9: On Point: Cleaves, H. James, John H. Chalmers, Antonio Lazcano, Stanley L. Miller, Jeffrey L. Bada 2008 "A Reassessment of Prebiotic Organic Synthesis in Neutral Planetary Atmospheres" Orig Life Evol Biosph (2008) 38:105-115
Response: This paper hurts Hurd's case against Meyer, as it shows that opinion is NOT divided about the earth's early atmosphere and that experts have largely rejected the view that the Earth's early atmosphere was reducing.
As noted, this paper contravenes Hurd's suggestion that the Earth's early atmosphere was reducing, as it states: "it is now generally held that the early Earth's atmosphere was likely not reducing, but was dominated by N2 and CO2."27 This concurs with a 2008 paper in Science, also co-authored by Bada, which admits, "Geoscientists today doubt that the primitive atmosphere had the highly reducing composition Miller used."28 In this regard, this recent paper thus validates Meyer's view of the composition of the earth's Early atmosphere.
Hurd cites this paper because it claims it "makes the entire redox issue moot. The prolific natural production of complex biomolecules can take place in neutral to even slightly oxic atmospheres." Hurd is correct that some of the experiments cited in this paper did produce amino acids, but it is quite a stretch to call it "prolific natural production of complex biomolecules." In fact, the production of molecules reported in this paper was neither complex, nor prolific, nor natural.
Regarding Hurd's claim that the products were "complex," the paper notes that what the research produced was "monomers"--some of the most simple organic molecules.
Regarding Hurd's claim that the production was "prolific," only four amino acids were produced in this experiment in any non-trivial quantity: serine, glutamic acid, glycine and alanine.
However, the main deficiency of this paper is that, like so many other origin of life experiments, it was intelligently designed to achieve the desired outcome, such that it's difficult to argue that it represented "natural" synthesis. First, some background.
The paper explains why non-reducing neutral atmospheres don't typically yield amino acids:
The main problem in the synthesis of amino acids and other biologically relevant organic compounds with non-reducing atmospheres appears to be the limited amount of hydrogen cyanide that is formed, which is a central intermediate in the Strecker amino acid synthesis and an important precursor for the synthesis of nucleobases.29
Ironically, such arguments mirror those made by Meyer in Signature in the Cell. Likewise, Kasting alluded to such problems when he wrote:
In the absence of a volcanic source of methane and ammonia, the post-heavy bombardment atmosphere was probably dominated by CO2 and N2 ... With regards to the origin of life, the key question is whether such an atmosphere could have generated formaldehyde (H2CO) and hydrogen cyanide (HCN). The former is needed for synthesis of sugars, the latter for synthesis of amino acids and nucleotides. ... Formation of HCN is much more difficult because it requires breaking both an N≡N and a C≡O triple bond (if one starts from N2 and CO2). Both bonds can be severed in the high temperature core of lightning discharges, but the resulting N and C atoms are more likely to combine with O atoms than with each other unless the atmospheric C:O ratio exceeds unity.30
Another problem for Miller-Urey experiments is that in neutral atmospheres, products like nitrate and nitrite tend to oxidize amino acids and break them down. Cleaves et al. (2008) thus intelligently designed their experiments in two ways to effectively convert a neutral atmosphere into a reducing environment:
(1) they maintain a constant pH using a buffer system (calcium carbonate), and (2) they add oxidizing inhibitor (ascorbic acid). (They acknowledge that "[a]scorbic acid is an unlikely prebiotic anti-oxidant," so then they add ferrous iron instead.)
Thus, in a key statement, this paper exposes the tricks that were used to 'season the soup' and produce amino acids:
Buffering the reaction solution with respect to pH and the addition of oxidation inhibitors such as ascorbic acid or Fe2+ prior to hydrolysis results in the recovery of up to several hundred times more amino acids than reported previously.31
By adding ferrous iron, the "oxidation inhibitors" were actually reducing agents intentionally added to convert a neutral environment into a reducing one. Thus, this paper was not like Miller's original research which set up a mixture of gasses and then simply passively assessed what organic molecules were produced. This experiment did not "revisit" the Miller-Urey experiments but rather carefully designed to convert a neutral environment into a reducing one that is favorable to producing amino acids.
The question is whether such oxidation inhibitors or pH buffers were available on the early Earth. A pro-ID chemist critiqued this paper privately to me as follows:
They talk about ferrous ion as if it merely trapped unwanted competing oxidative species from destroying amino acids, etc., but given the large excesses, what they are really doing is using ferrous ion to give them a reducing chemical environment. Once this is achieved, we are back to Miller's highly reducing atmosphere scenario. While this may be reasonable from a variety of perspectives, it too begs the question: is the neutral atmosphere plus ferrous ion in the ocean a 'random condition' or a designed one? To be honest, there is no way to know for sure. At this point, the science has left the question unanswered.
The chemist continued saying that by adding all the ingredients, "They switched from passive observers to intentional controllers."
Is it appropriate to season the prebiotic soup with buffers and ferrous iron? The authors claim their position is "reasonable," but admit they don't know really the answer to that question, tentatively stating: "Organic synthesis from neutral atmospheres may have depended on the oceanic availability of oxidation inhibitors as well as on the nature of the primitive atmosphere itself."32 The authors don't know if their experiment was "natural," and Hurd's claim that it was "natural" is a bluff.
There's one final artificial aspect of this experiment, as the authors note:
In our analytical procedure, the reaction mixture was acid hydrolyzed in order to convert any precursors to amino acids. Under natural oceanic conditions with the pH near neutral, hydrolysis of the precursors would likely proceed slowly, but nevertheless take place over reasonably short geologic time scales. Acid hydrolysis simply expedites this hydrolysis process in the laboratory.
Surely speeding up the reactions is necessary for practical experimental concerns, but speeding up the reactions certainly prevents many opportunities for natural conditions to break down fragile organic molecules like amino acids (which can have short half-lives). This speeding up of the reaction may provide unnatural protections to the organic products.
Contra Hurd, it has not been established that this experiment showed anything "natural."
One noteworthy--though ironic--part of this paper is that it gives a serious, non-negative citation to Jonathan Wells' book Icons of Evolution as providing a legitimate critique of chemical evolution:
The perceived problems in the synthesis of organic compounds under neutral atmospheric conditions have also been represented by some as evidence against evolutionary approaches to the study of the origins of life (Wells 2000).33
By recommending this paper, has Hurd unwittingly endorsed Jonathan Wells' critique of the origin of life as legitimate?
Part VIII: The Reducing Oasis?
Hurd also mentions the possibility of pockets of a "strongly reducing oasis" in an overall non-reducing atmosphere--although he does not cite a single paper that presents research in favor of that hypothesis. This best Hurd does is to cite a paper co-authored by Stanley Miller with one sentence alluding to what Hurd calls the "reducing oasis" hypothesis:
Although amino acids and a wide array of other biochemical monomers are readily produced from reduced gas mixtures, the geochemical relevance of these model atmospheres has been questioned (Holland 1962; Abelson 1966). As a result, some researchers now either consider the atmospheric composition used in the Miller-Urey experiment implausible, or suggest that reducing conditions only existed in localized regions such as volcanoes or hydrothermal vents.34
Wait a second: Abelson's 1966 paper is also cited by Meyer on the same point! Hurd charges Meyer's discussion is "outdated," but why doesn't he call this paper "outdated" if it uses the same citation from Abelson?
In any case, the "oasis" hypothesis has some severe problems of its own, not the least of which is that it limits the number of zones that can produce amino acids to small oases. This will drastically reduce the amount of soup that can be produced, and dramatically decreasing probabilistic resources available for the origin of life. For all its pitfalls, the advantage of the prebiotic soup hypothesis is that it postulated a vast sea of prebiotic monomers on the early earth. But the "oasis" hypothesis drastically limits the amount of soup available.
What is more, these oases are not hospitable environments for prebiotic monomers. Volcanoes are hot, which will quickly destroy organic molecules.35 Hydothermal vents have all the problems that come with being hot, but add to them the complication of being underwater, a location which prohibits polymerization of amino acids into longer chains like peptides.36 Like so many areas of origin of life thinking, solving one problem produces many more. Hurd has not demonstrated that this relatively new and highly tenuous "oasis" hypothesis deserves any attention from Meyer.
Part IX: Lesson Learned About Spotting a Citation Bluffer
In the end, we've seen that six of Hurd's nine citations were literature bluffs. Another two were extremely weak citations. One citation was on-point, but requires highly intelligently engineered experiments that may not mimic natural Earth conditions.
Some unwitting Amazon.com readers will surely read Hurd's review of Signature in the Cell and be bluffed into thinking Hurd has made a strong critique. What are such readers to do if they don't have time, resources, or background knowledge to delve into the scientific literature? Thankfully, there are some clues that will help the non-expert determine when someone is literature bluffing.
There's nothing necessarily wrong with simply citing a research paper without further commentary. But generally, you can tell if someone is citation bluffing when they list long string of citations without giving any quotes from the papers or any meaningful description of what the papers found.
While it can be difficult to prove that someone is citation bluffing without going back to the original articles themselves, it is possible to know that someone is NOT citation bluffing without reading the original papers. This is because, if a person provides actual quotes from the papers and discussion of their findings, then you can understand what the paper argued without going back and reading it.
It's still advisable to go back and read the original sources that are cited. But this episode highlights a major difference between Hurd's review and this rebuttal to him: Hurd cited a string of papers without any quotes or commentary, and many of them turned out to be wholly irrelevant--or even in opposition--to the point he was making. In contrast, in the vast majority of cases I have provided quotes from the papers I'm citing so that the reader can immediately know what they say.
There's no need to hide the findings of the scientific literature. Strange and suspicious that Hurd apparently feels the need to do so.
In closing, Hurd scoffs at Meyer's undergraduate degree, as if the fact that his "under-graduate geology degree was from a religious school" means it therefore yielded a biased and incomplete education. I have no desire to sneer back at Hurd. But since Hurd raised the issue of ideological bias, one has to wonder: Has Hurd's viewpoint biased him to make irrelevant citation bluffs?
[2.] Dehydration synthesis of peptides makes it difficult to imagine how amino acids would link to form proteins in the aqueous of the prebiotic soup. As the U.S. National Academy of Sciences observes: "In water, the assembly of nucleosides from component sugars and nucleobases, the assembly of nucleotides from nucleosides and phosphate, and the assembly of oligonucleotides from nucleotides are all thermodynamically uphill in water. Two amino acids do not spontaneously join in water. Rather, the opposite reaction is thermodynamically favored at any plausible concentrations: polypeptide chains spontaneously hydrolyze in water, yielding their constituent amino acids." Committee on the Limits of Organic Life in Planetary Systems, Committee on the Origins and Evolution of Life, National Research Council, The Limits of Organic Life in Planetary Systems, p. 60 (National Academy Press, 2007).
[3.] Stephen C. Meyer, Signature in the Cell: DNA and the Evidence for Intelligent Design, p. 224 (HarperOne, 2009).
[4.] Adam P. Johnson, H. James Cleaves, Jason P. Dworkin, Daniel P. Glavin, Antonio Lazcano, Jeffrey L. Bada, "The Miller Volcanic Spark Discharge Experiment," Science, Vol. 322:404-405 (October 17, 2008).
[5.] Deborah Kelley, "Is It Time To Throw Out 'Primordial Soup' Theory?," NPR (February 7, 2010).
[6.] Kevin Zahnle, Laura Schaefer, and Bruce Fegley, "Earth's Earliest Atmospheres," Cold Spring Harbor Perspectives in Biology (2010).
[7.] Dante Canil, "Vanadian in peridotites, mantle redox and tectonic environments: Archean to present," Earth and Planetary Science Letters, Vol. 195:75-90 (2002) (internal citation removed).
[8.] James F. Kasting and David Catling, "Evolution of a Habitable Planet, " Annual Review of Astronomy and Astrophysics, Vol. 41:429-463 (2003).
[9.] A. Ricardo, M. A. Carrigan, A. N. Olcott, S. A. Benner, "Borate Minerals Stabilize Ribose," Science, Vol. 303:196 (January 9, 2004).
[10.] James F. Kasting and David Catling, "Evolution of a Habitable Planet," Annual Review of Astronomy and Astrophysics, Vol. 41:429-463 (2003).
[11.] Michael John Russell, "The Hazy Details of Early Earth's Atmosphere," Science, Vol. 330:754 (November 5, 2010) (internal citations omitted).
[12.] E.T. Wolf and O. B. Toon, "The Hazy Details of Early Earth's Atmosphere," Science, Vol. 330:754-755 (November 5, 2010).
[13.] E. T. Wolf and O. B. Toon, "Fractal Organic Hazes Provided an Ultraviolet Shield for Early Earth," Science, Vol. 328:1266-1268 (June 4, 2010).
[14.] Heinrich D. Holland, "When did the Earth's atmosphere become oxic? A Reply," The Geochemical News, Vol. 100:22-22 (July 1999).
[15.] James F. Kasting, "The Rise of Atmospheric Oxygen," Science, Vol. 293:819-820 (August 3, 2001).
[16.] James F. Kasting, "Ups and downs of ancient oxygen," Nature>, Vol. 443:643-645 (October 12, 2006).
[17.] Kosei E. Yamaguchi, "Evolution of the atmospheric oxygen in the early Precambrian: An updated review of geological 'evidence'," Frontier Research on Earth Evolution, Vol. 2 (2005).
[18.] The lines of evidence include:
Low Oxygen: Loss or retention of Fe in paleosols; Mineralization mechanisms for U ores; Occurrence of O2-sensitive heavy minerals such as detrital components in ~3 Ga sandstones; Age distribution of red beds; Low content of redox-sensitive trace metals; Age distribution and formation mechanism of iron formations; Discovery of eukaryotes; Sulfur isotopic composition of sulfides and sulfates for the secular changes in the S cycle; Mass-independent S isotope fractionation; Secular changes in the N cycle; Secular change of Th-U-Pb systematics of mantle;
High Oxygen: Discovery of laterites at the top of a ~2.3 Ga paleosol profile and its Fe isotope studies; Common occurrence of Fe loss in paleosol of all ages, including the Phanerozoic, caused by variable processes including alternation by hydrothermal fluids, organic acids produced by soil biota; Development of oxidized paleosols of ~2.7 Ga in age; Hydrothermal mineralization of uraninite and pyrite in U ores; Survival of detritatl uraninite and pyrite in Phanerozoic sediments; Post-depositional mineralization (rather than detrital transport) of siderite; Discovery of 2.7 Ga old red beds; Occurrence of ferric oxide crust of pillow lava; Occurrence of iron-formations in Neoproterozoic; Geochemistry of banded iron-formations; Large variations in the S isotopic compositions of sulfides in sediments; Abundance of organic carbon in Archean shales suggesting an operation of aerobic recycling; Redox-sensitive trace elements in black shales and normal shales; Discovery of biomarkers for cyanobacteria and eukaryotes in Archean black shales; Fe isotope compositions of black shales; N isotope compositions of organic matter and clays in black shales;
[19.] See Hiroshi Ohmoto, Yumiko Watanabe, Hiroaki Ikemi, Simon R. Poulson & Bruce E. Taylor, "Sulphur isotope evidence for an oxic Archaean atmosphere," Nature, Vol. 442:908-911 (August 24, 2006).
[21.] Richard A. Kerr, "Great Oxidation Event Dethroned?," Science, Vol. 324:321 (April 17, 2009).
[22.] Bernd Michael Rode, "Peptides and the origin of life," Peptides, Vol. 20:773-786 (1999).
[23.] H. James Cleaves, John H. Chalmers. Antonio Lazcano, Stanley L. Miller, & Jeffrey L. Bada, "A Reassessment of Prebiotic Organic Synthesis in Neutral Planetary Atmospheres," Origin of Life and Evolution of the Biosphere, Vol. 38:105-115 (2008).
[24.] David C. Catling & Mark W. Claire, "How Earth's atmosphere evolved to an oxic state: A status report," Earth and Planetary Science Letters, Vol. 237:1-20 (2005).
[25.] James F. Kasting and M. Tazewell Howard, "Atmospheric composition and climate on the early Earth," Philosophical Transactions of the Royal Society B, Vol. 361:1733-1742 (2006), citing David C. Catling, "Comment on 'A Hydrogen-Rich Early Earth Atmosphere'," Science, Vol. 311:38a (January 6, 2006).
[26.] Stephen C. Meyer, Signature in the Cell: DNA and the Evidence for Intelligent Design, p. 224 (HarperOne, 2009).
[27.] H. James Cleaves, John H. Chalmers. Antonio Lazcano, Stanley L. Miller, & Jeffrey L. Bada, "A Reassessment of Prebiotic Organic Synthesis in Neutral Planetary Atmospheres," Origin of Life and Evolution of the Biosphere, Vol. 38:105-115 (2008).
[28.] Adam P. Johnson, H. James Cleaves, Jason P. Dworkin, Daniel P. Glavin, Antonio Lazcano, Jeffrey L. Bada, "The Miller Volcanic Spark Discharge Experiment," Science, Vol. 322:404-405 (October 17, 2008).
[29.] H. James Cleaves, John H. Chalmers. Antonio Lazcano, Stanley L. Miller, & Jeffrey L. Bada, "A Reassessment of Prebiotic Organic Synthesis in Neutral Planetary Atmospheres," Origin of Life and Evolution of the Biosphere, Vol. 38:105-115 (2008).
[30.] James F. Kasting, "Earth's Early Atmosphere," Science, Vol. 259:920-926 (February 12, 1993).
[31.] James F. Kasting, "Earth's Early Atmosphere," Science, Vol. 259:920-926 (February 12, 1993).
[32.] H. James Cleaves, John H. Chalmers. Antonio Lazcano, Stanley L. Miller, & Jeffrey L. Bada, "A Reassessment of Prebiotic Organic Synthesis in Neutral Planetary Atmospheres," Origin of Life and Evolution of the Biosphere, Vol. 38:105-115 (2008).
[33.] H. James Cleaves, John H. Chalmers. Antonio Lazcano, Stanley L. Miller, & Jeffrey L. Bada, "A Reassessment of Prebiotic Organic Synthesis in Neutral Planetary Atmospheres," Origin of Life and Evolution of the Biosphere, Vol. 38:105-115 (2008).
[34.] James F. Kasting, "Earth's Early Atmosphere," Science, Vol. 259:920-926 (February 12, 1993).
[35.] The short half-lives of many prebiotic monomers is discussed in Matthew Levy and Stanley Miller, "The Stability of the RNA bases: Implications for the origin of life," Proceedings of National Academy of Science, USA, Vol. 95:7933-7938 (July 7, 1998).
[36.] Dehydration synthesis of peptides makes it difficult to imagine how amino acids would link to form proteins in the aqueous of the prebiotic soup. As the U.S. National Academy of Sciences observes: "In water, the assembly of nucleosides from component sugars and nucleobases, the assembly of nucleotides from nucleosides and phosphate, and the assembly of oligonucleotides from nucleotides are all thermodynamically uphill in water. Two amino acids do not spontaneously join in water. Rather, the opposite reaction is thermodynamically favored at any plausible concentrations: polypeptide chains spontaneously hydrolyze in water, yielding their constituent amino acids." Committee on the Limits of Organic Life in Planetary Systems, Committee on the Origins and Evolution of Life, National Research Council, The Limits of Organic Life in Planetary Systems, p. 60 (National Academy Press, 2007).