Review Reports

Comment

Response

I carefully read the paper entitled “Dating Petroglyphs Using Measurements of Manganese Accumulation in Rock Varnish: New Research Findings and Their Implications” and I found it quite interesting. But I also found some problems in the structure and general organization of the manuscript that suggest the need for a mayor revision.

I have the following comments for this paper.

• First of all, the abstract must be rewritten following MDPI guidelines. In the abstract, authors must indicate: background, methodology, summary of results, and conclusions with future perspectives. In its current form, the abstract is background only.

• The only component of the MDPI guidelines missing was methods. We have now added methods to the abstract in the revised manuscript

• The number of self-citations is really excessive, around 40%.

• Normally, we agree and try to avoid self-citation.
• For this particular paper, there are two reasons for this high level. First, a large number of citations are necessary because we are using samples obtained from prior research. This accounts for 30% of the citations. Second, the authors are among the first to use rock varnish to date petroglyphs, and hence their papers are an unavoidable part of the background information.

• In the introduction, the authors outline the state of the art in petroglyph dating research, but the purpose of their work and research is not clearly defined. Do the authors start from previously collected data? Do they conduct new sampling?

• We start with the premise that rock art dating is critical to archaeology but that there are still difficulties in doing so &, although pXRF petroglyph dating is appealing, it has not been adequately evaluated
• The purpose of the work is clearly defined as follows in the introduction – “We examine here certain implicit assumptions of the pXRF approach. As indicated above, the primary assumption is that Mn systematically accumulates in rock varnish over time, allowing it to be used to assign specific ages to petroglyphs.”
• We repeatedly stated that we used existing, archived samples from our previous published studies.
• The use of archived samples was necessary because of the destructive nature of the mechanical removal of varnish from a rock varnish coating which Indigenous tribal stakeholders would never allow, given the existence of the archived samples to carry out this research. Yet such samples are essential to our analysis

• Page 2, line 70: the authors affirm: Our research, described below, indicates that:
• But these are results? Or what?

• Yes. These are results, as now stated.

In the Introduction the authors must report the state of art, the aim of their research, the methodology used and why this methodology was chosen to reach the desired results.

The comment above states that “In the introduction, the authors outline the state of the art in petroglyph dating research.” We are confused why, in this comment, the implication is that this is missing.

The introduction in fact includes all of these components except for methods, which we have now added. We explain that the we used samples already collected during prior investigations, with a mixture of electron microscope methods. Because we use different SEM methods for the various analyses, it would require excessive length to describe each here. We include those details, accordingly, in the appropriate following sections.

I understand that the topic is peculiar and that the dating of petroglyph is a challenging goal, but a scientific paper should follow some standards in presenting the research.

Before we delve into explanations on how we have modified the paper to meet the concerns of Reviewer #1, we are reluctant to make massive changes because the information thought to be missing by reviewer #1 is clear to Reviewer #3:

“It presents its rationale, methods and findings clearly, and I particularly appreciate the clear contours and limitations that its authors place on what they did and found.”

Our history of publishing papers in major international science journals over the last 45 years demonstrates, unequivocally that we have repeatedly met the desired standard.

Still, we have taken to heart the concerns of reviewer #1. We do not want to confuse or confound our methods that are truly very simple.

Perhaps the difficulty is that the approach we used in evaluating the role of microcolonial fungi, “inherited” varnish, and Mn in silica glaze was and is extremely simple.  We used the ecological concept of “transects” to obtain quantitative insight as to the magnitude of these issues.

       The idea of examining BSE and SE imagery totaling 5000 µm or more and adding up abundance was apparently not clear to reviewer #1.  We tried to clarify our simple strategies through better wording and examples in the revision.

      Please note, however, that our section on the use of the electron microprobe was more detailed and not commented on by reviewer #1

• In the Methods paragraph the authors state the following: “We examined four natural conditions and processes that may affect the efficacy of pXRF measurements of Mn accumulation in a rock varnish coating as a systematic time signal for this study, as outlined in the following. We note at the outset that we analyzed existing samples which we had collected for previous research for this current examination. With one exception, these are all from petroglyphs. Given that only certain specimens were appropriate for each respective type of analysis, this limited our sample sizes to only a handful cases for two out of four of our cases. Our other two analyses both involved more than 30 samples each. We explain the rationale for our sample selection for each independent concern below. Given the small sample sizes overall, however, our results should be considered preliminary for this fact.”

• Yes, & this includes a description of our sampling sizes.
• But perhaps the reviewer is wondering about the size of the flakes removed from the petroglyphs? This information is explained in each paper, but is best summarized as millimeter-scale flakes.

But no description of the samples is reported in the article, no details of the SEM-EDS analytical procedure and instrumental conditions. What is the sample size? I read only general assessments but no details about the analysis performed and the samples used. The reader must know what kind of samples have been used and the electronic microscope characteristics

The sample sizes (of number of petroglyphs analyzed) are repeatedly described in the cited papers and, for this paper, in the original manuscript, in the Methods background, in each of the 4 specific methods descriptions, and in the results. We in fact caution, twice, that our findings should be considered preliminary in recognition of our limited sample sizes.  Other details were provided in the cited papers.  We felt it inappropriate to repeat that information for this paper. However, we hope that the material added to each methods section adds sufficient clarity. 

It is true that many data have been published in previous articles, but the reader would be helped by a summary table reporting the characteristics of the samples used and the types of conditions and processes to which the authors refer in the lines above.

Neither reviewer #2 nor #3 requests any such change or expresses any difficulty with how we have presented our data and sources. Scientific papers commonly, if not universally, follow the practice we have used here, and there is no need to confuse the body of scholarship on this subject.

Please revise this paragraph by adding the missing information

• Paragraph 3.1 is complete obscure for me. In the first lines the authors assess: MCF dissolved 30%, 22%, 37%, 15% and 60% of the rock varnish cross-sections that had formed in five petroglyphs analyzed from the Mojave and Sonoran deserts (Figure 1). But how can derive these percentage from the Figure 1?

• The paragraph has been completely rewritten into three paragraphs

Figure 1 must be explained. I suggest using letters to differentiate the images within figure 1, i.e. 1A, 1B, 1C.

  Figure 1 is now explained in the text of Section 3.1 and in a revised caption.

We feel that lettering the figure would make it unnecessarily noisy and prefer not to alter it that way

Please check the doi in reference 36 because it doesn't work.

It worked fine when we re-checked it.

• In the caption of figure 1 the authors write: See Whitley and Dorn [38] for an explanation of the layering and dating of this petroglyph based on the image on the right). I'm sorry, but I don't agree with the fact that the reader of this article should have to read the explanation of an image in a previous article.

• The caption to figure 1 was rewritten to provide what we hope is a clearer explanation, w/o need to consult earlier papers.

I am aware that the authors have extensive experience and numerous publications on the topic of this article, but each new work must report the data extensively to allow the reader to understand what they are reading and seeing, without having to read dozens of other articles to understand the data.

To do as the reviewer suggests would expand the length of the paper ten-fold.  Further, journal editorial policies almost universally prohibit the publication of previously presented material which, in essence, is what is implied by this request. Again, we have made changes to the paper to clarify methods as requested by reviewer #1, we have tried to reach a good balance between reviewers #1 versus #2, #3.

• Paragraph 3.2. The authors write: Inherited varnish patches comprised 3% (CM 15), 2% (Fort Irwin 96-4), 5% (Fort Irwin 96-16) and 3% (Cima 1-1) of their cumulative cross-sectional profile lengths in four analyzed petroglyphs.
• Can the authors explain where they got these percentage data?

• We explained how the percentage data were obtained in the methods. We have added a new paragraph here for clarification.

• Paragraph 3.3, lines 245-246: “Mn-containing areas of silica glaze are themselves dark in color due to their Mn contents, making them difficult to distinguish from varnish in the field”.

Mn-containing areas are lighter by BSE imaging not dark. The sentence is not clear.

• When seen in the field by eye or via hand lens, Mn-containing areas of silica glaze are dark. They are almost black.
• And yes, in the BSE imaging, Mn is quite bright since it is Mn-rich.
• Since the audience consists mostly of those with field experience, we needed to stress that the presence of Mn in silica glaze is dark and hence looks similar to rock varnish when viewed optically in the field.
• We have clarified this in the text and in a new sentence added to Figure 3.

• In conclusion, the article examines the issues related to dating petroglyphs based on XRF data, considering that manganese has diverse sources. Therefore, I would say the title is inappropriate for the manuscript's content. In fact, it doesn't discuss dating, but rather issues related to determining manganese with pXRF and subsequent dating.

• We understand the reviewer’s perspective that the current implication of our data cause issues with pXRF.
• We believe it is very important to broaden the implications of this research well beyond just pXRF.
• The broader issue is whether it is appropriate for manganese accumulation to be the foundation of a petroglyph dating technique. pXRF is just one way of trying to measure Mn. There are others, and the implication of our findings could apply to many other possible methods used in the future.

I therefore also suggest changing the title to: Problems (or Limits) of Dating Petroglyphs Using Measurements of Manganese Accumulation in Rock Varnish: New Research Findings and Their Implications

We changed the title as suggested