Talk:Cretaceous–Paleogene boundary

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Page title (2007)[edit]

The KT boundary is either a) a moment in time straddling the Mesozoic and Cenozoic eras; b) a sequence of rocks covering that period. The content of this article is rather loosely defined, but it isn't really either of those. OM, can you explain what you mean by this comment: "The extinction is separated from geological activity."? Would a better title perhaps be "Geological signature of the K-T boundary", or similar? Badgerpatrol 23:05, 10 September 2007 (UTC)

But isn't the KT boundary a geological signature? The reasons I want to rename it is that if you look back at the links in other articles, it's getting confusing what article is referring to what. I think we should keep K-T boundary a strictly (or close to strictly) geological article, whereas the K-T extinction event more biological, with some overlap. I don't know what would be a good title--Geological events at the K-T boundary? Not sure. OrangeMarlin Talk• Contributions 23:13, 10 September 2007 (UTC)
Well...it is and it isn't. Technically the "KT boundary" is a specific junction between sedimentary layers at a section near El Kef, a town in Tunisia [1], and by analogy similar sections worldwide. More abstractly, it's a moment in time. I think the reason I have a bit of a problem with the title is that the actual article content mixes up process and observation- i.e. geological causation (impacts, sea level change) with geological observations (craters, shocked quartz, coarsening-upward sequences etc.) and doesn't necessarily match the page name. Reading the title, my expectation would be to find a discussion of the sedimentology and stratigraphy of the boundary layers, locations of sections worldwide, a discussion of the stratotype and geochronology...i.e. an altogether dryer and more boring article about geology.... The stuff about impacts etc could be better placed elsewhere (albeit the impact signature should definitely be mentioned extensively as a very important feature of boundary sediments). I suggest we re-write the article to suit the title in fact, rather than changing the title to suit the article- what do you think? Badgerpatrol 00:39, 11 September 2007 (UTC)

Suggestions for improving this and the other article[edit]

At present this article reads a bit odd to the general reader.

  1. Intro
    1. For us non-geologists, what is a "geological signature"?
    2. "a thin band" — a thin band of what?
    3. "The boundary marks the end of the Mesozoic Era, and the beginning of the Cenozoic Era." This sentence needs something more to turn it into a geol statement rather than a chron statement.
  2. Sections — apart from the footnotes appendix, the article has only one section, albeit with subsections. A substantial article with only one section is kinda weird. Could its subsections be raised to top-level sections?
  3. From the 4th paragraph of the Alvarez subsection, the article starts talking about "the extinction" as though the reader already knows about it. Before referring to the extinction in this way, the article needs to explain in summary what the extinction is. And it should link to the full article on the extinction event.
  4. A lot of the content is duplicated in the Cretaceous–Tertiary extinction event article. It is poor organisation to duplicate info in detail in 2 related articles. The extinction event article should concentrate on the extinction and cover the geol info in summarised form only. Likewise this article should concentrate on the geol (as it does) but cover the extinction in summary, as per previous point. Nurg (talk) 09:52, 8 January 2008 (UTC)
This material was cut out of Cretaceous–Tertiary extinction event which explains the duplication and some of the other issues you raise. Really, this is talking about extinction mechanisms which are co-incident with, but not the same as, the KT boundary. It would perhaps be better to talk about the actual geology (available sections, sedimentology, stratigraphy, preservation, reworking). The KT boundary (as I state above) is either a) a moment in time (notable only for the extinction and thus covered in that article) or b) a collection of rock strata (boundary clay, fireball layer, etc etc) exposed either sub-aerially or in found in deep sea cores. Currently, the article doesn't really talk about either of those. Before the inevitable ruckus kicks off with anyone, that's not a criticism, it's an observation. Badgerpatrol (talk) 12:35, 7 May 2008 (UTC)
Well, I know I'm late to the party, but I only encountered the phrase "Cretaceous–Paleogene extinction event" and abbreviation "Pg" for the first time yesterday, whilst researching some sedimentary basins on the Geoscience Australia website. Clearly, I'm no geologist! ;-) OK, so the "Cretaceous–Paleogene extinction event" is the old "Cretaceous–Tertiary"or "K-T" extinction event; of course, any active field revises its terminology as needs and understanding changes. But one thing confuses me: why are there two separate articles at all? I assumed that the geological boundary would have the same name and would be described in the same article as its major evidence ...! As a "general reader" (my scientific specialty, if any, is physics), I don't see the need for Wikipedia articles to fuss over the boundaries between scientific disciplines. My guess is that one article represents the POV of geology, the other that of evolutionary biology. Given the large amount of content duplication, the two articles together are much less informative - and more work to read - than they could be if rolled back into one coherent story. IMO, one article would serve the Wikipedia audience better than two. yoyo (talk) 00:18, 2 March 2016 (UTC)

Fixed error[edit]

I've slightly altered the formatting of the initial quoted date in the first line because it seemed to be giving me a recurrent error (see page hist) that I couldn't fix. If anybody knows the problem, please change it back to however you wish. Badgerpatrol (talk) 12:28, 7 May 2008 (UTC)

In Our Time programme about this[edit]

The BBC programme In Our Time presented by Melvyn Bragg has an episode which may be about this subject (if not moving this note to the appropriate talk page earns cookies). You can add it to "External links" by pasting {{In Our Time|The KT Boundary|p003k9d0|K-T_Boundary}}.

James F. (talk) 21:28, 16 September 2010 (UTC)

Article name (2012)[edit]

Since the old name of Cretaceous-Tertiary extinction event has been changed to the Cretaceous–Paleogene extinction event, or K-Pg, shouldn't this article be renamed to the K-Pg boundary? I know that K-Pg boundary redirects here, but the names should be consistent with the extinction event. I have no clue how to rename an article over a redirect, so I'm hoping that someone watching this article and knows how to do it can make it happen. SkepticalRaptor (talk) 21:55, 28 April 2012 (UTC)

Requested move (2012)[edit]

The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the move request was: page moved per RockMagnetist and WP:AT's note on consistency. -- JHunterJ (talk) 10:56, 18 May 2012 (UTC)


K–T boundaryCretaceous–Paleogene boundary – Since K-T boundary and K-T extinction event have been changed to K-Pg because Tertiary (T) has been deprecated. We should rename this article. We will also need to change all of the redirects, so if someone could help me out on how to do it, I'd appreciate it. SkepticalRaptor (talk) 01:48, 10 May 2012 (UTC)

  • Oppose WP:JARGON, WP:UCN. The other article seems to have been moved based on Jargon usage, not common usage in WP:RS. WP:RS does not say that RSes are restricted to one particular field's research journals. 70.24.251.208 (talk) 09:29, 10 May 2012 (UTC)
  • Comment: I, too, am not entirely convinced that common usage has caught up with geologists for this event. Powers T 15:45, 10 May 2012 (UTC)
  • Comment: Please see Cretaceous–Paleogene extinction event. It should be consistent. And it doesn't matter that it's not the popular wording, it's what is used by the officials who name these things. We have redirects for those individuals that lack any education in this matter. Tertiary is gone from usage, because it was based on pre-Darwin ideas about the earth. It's silly. WP:Jargon has no applicability here, it's like not having Pluto as a planet. Oh wait it isn't a planet anymore. Again, any logic here should be used at the sister article, because K-Pg is now used everywhere. This article is misnamed if the event itself is called the K-Pg extinction event. This is the boundary layer. I would suggest about 10 seconds of research over there. And yeah, the International Commission on Stratigraphy gets to make that decision. Based on the logical fallacies above, then we don't rename species here, because no one has a right to do that until the uneducated masses of Wikipedia readers get on board. Or companies that change names won't be reflected here. This should be a no-brainer. But what can I expect from Wikipedia? SkepticalRaptor (talk) 19:17, 10 May 2012 (UTC)
    • Making lots of friends today, I see? WP:COMMONNAME is a well-established guideline and should be followed without good reason not to. We try to put articles under the title by which people know them, not the titles that any official organization would like them to be called. Powers T 19:27, 10 May 2012 (UTC)
      • This isn't Facebook, so no, don't give a shit about making friends here. However, again with the logical fallacies. You're using a strawman argument rather than discussing the main article, the K-Pg extinction event which changed the name. If you have a tiny bit of energy, go read the same lame arguments over there, which failed. However, my suggestion is that if you think you're right, then you better go request a name change of the main article. Because we want Wikipedia to be the worst piece of science ever. I'll await a non-fallacious argument from you. SkepticalRaptor (talk) 19:46, 10 May 2012 (UTC)
        • Civility is a pillar around here, Mr. Raptor. I suggest you start adhering to it. Powers T 13:26, 11 May 2012 (UTC)
    • WP:OFFICIALNAME -- official names are weighted less than common names. 70.24.251.208 (talk) 05:01, 11 May 2012 (UTC)
  • Support The people invoking WP:COMMONNAME don't seem to have read the discussion for moving Cretaceous-Paleogene extinction event. I'll transcribe the clinching argument here:

A closer look at WP:COMMONNAME reveals that "more weight should be given to the name used in reliable sources published after the name change than in those before the change." Note the word "reliable". A quick search of articles since 2004 on Google Scholar strongly supports C-Pg. Alternative names like "K-T extinction" can be redirected, so a name change is not likely to cause confusion, especially if the former name is mentioned in the first paragraph.

RockMagnetist (talk) 16:30, 11 May 2012 (UTC)
Actually reading policy isn't exactly common amongst most people who quote guidelines. Good job.SkepticalRaptor (talk) 05:22, 14 May 2012 (UTC)
Although there is something in what you say, I think that common sense is needed here. First, it's a stretch to say that "K-Pg boundary" is jargon while "K-T boundary" is not. I don't think that is the intent of the policy. I grant you that the official name does not have to be the article title. But WP:OFFICIALNAMES defers to WP:COMMONNAME for deciding when to use the official name.
Although news articles are (somewhat) reliable, they are seeking a balance between what the scientists say and what they think the public can understand. And I think that balance is shifting. Several of the articles using variants of "K-T" also mention that "K-Pg" is now the official name.
I don't think it is a very important issue. Calling the article "K-T boundary" and referring to "K-Pg boundary" in boldface would be just as good. RockMagnetist (talk) 15:16, 12 May 2012 (UTC)
  • Support - per RockMagnetist. Mikenorton (talk) 23:17, 11 May 2012 (UTC)
  • Support - per RockMagnetist. Paul H. (talk) 02:09, 12 May 2012 (UTC)
  • Oppose -- I'm a professional geologist, and this change is news to me. The proposed name change would just confuse ordinary readers. Best to mention the new work in the article, for now. --Pete Tillman (talk) 13:50, 12 May 2012 (UTC)
How specialized we scientists have become! I presume you're not denying, though, that it is now the official name. I don't see how it would cause confusion if the article is written properly. I have added a boldface reference to K-T boundary in the first sentence. That makes for redundancy with a later statement in the lead, but follows the recommendation of WP:COMMONNAME. RockMagnetist (talk) 14:49, 12 May 2012 (UTC)
Far outside, my specialty, I grant... But Cretaceous–Paleogene is an odd construction -- why not Maastrichtian - Paleogene, if we're taking it to stages? Bad choice by whoever picked this as a replacement name, in my (professional) opinion. --Pete Tillman (talk) 17:50, 13 May 2012 (UTC)
The Paleogene is now a period or system ... not a stage. Yeah, them young whipper-snappers just keep changin' things to confuse old foggies like me too :) Vsmith (talk) 02:01, 14 May 2012 (UTC)
Could you guys be be thinking of Paleocene? RockMagnetist (talk) 16:14, 14 May 2012 (UTC)
I think that, strictly speaking, the extinction defines the boundary and does not properly belong to the Cretaceous or whatever follows it ;) So Cretaceous extinction might be a misnomer, despite its popularity. RockMagnetist (talk) 04:55, 13 May 2012 (UTC)
The biggest of the "Big 5" is often called the end-Permian event, but I've never seen that applied to the K-T --Pete Tillman (talk) 17:55, 13 May 2012 (UTC)
  • Support per above ... even if I personally dislike it (why isn't Pluto still a planet ism :) Vsmith (talk) 02:01, 14 May 2012 (UTC)
  • Support per RockMagnetist. SkepticalRaptor (talk) 05:28, 14 May 2012 (UTC)
    • As the nominator, your support is presumed. Powers T 17:48, 16 May 2012 (UTC)
  • Comment - It is sad that some people see this as a black and white issue and denigrate those who disagree. It's not a simple issue at all. For example, in a search of "Cretaceous extinction" in Google books, not one of the books on the first page of hits refers to the extinction as Cretaceous-Paleogene. Peter Ward, a specialist in the extinction and a notable popular science writer, is still referring to it as the Cretaceous Tertiary extinction in a book published in 2010. My feeling is that WP:COMMONNAME does not really decide the issue after all: the primary sources come out in favor of change, but the best secondary sources oppose the change.
Here is an amusing irony. Few of the references in this article support the rename. In the lead, the third reference is a dead link, the second (Fortey's book) does not mention the Paleogene at all, and the first links to a site in Chinese!
I think that the important issue may be consistency. Not so much with Cretaceous-Paleogene extinction event, which just got renamed, but with the statements in Tertiary and Paleogene and a few timelines used by several Geology articles. None of the latter can be changed, so it makes sense to change this article. But the references need updating!!! RockMagnetist (talk) 16:03, 14 May 2012 (UTC)
The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Age of the K-Pg Boundary[edit]

This page still makes reference to 65.5 million years ago, but the International Commission on Stratigraphy has determined that the Cretaceous terminates instead at 66 million years ago ( as can be seen in this picture http://stratigraphy.org/ICSchart/ChronostratChart2013-01.jpg). I'm unsure of the most delicate way to fix these references in the article. Gruekiller (talk) 07:11, 13 December 2013 (UTC)

Name change: K-T to K-Pg? (2015)[edit]

Reading this article today was the first time in my life that I've ever heard of the name change to Cretaceous-Paleogene. Having been impressively more obsessed with dinosaurs as a child than your average 6 year old boy, I'm a little a disconcerted that I missed this important change in nomenclature. I'm even more disconcerted that there is absolutely no time spent in this article, nor in other related K-T/K-Pg articles, on when and why the name was changed. If someone is aware of this information, it should definitely be included in this article. ---Puff (talk) 18:09, 10 February 2015 (UTC)

See Tertiary - second sentence and first four refs. Vsmith (talk) 01:41, 11 February 2015 (UTC)
Well, I appreciate the link. I have now seen Tertiary and that article does no more to explain the reason for the change than any of these others, nor does it or the references provide a date. The only new information this article provides is that it was the International Commission on Stratigraphy that made the change. I suppose when I have time (which is never) I can try digging through ICS archives to try and find the information I'm looking for.---Puff (talk) 20:07, 11 February 2015 (UTC)
Obviously, older sources and slower sources will not have caught up to the name change. The Tertiary period was split up into the Paleocene and Neogene periods by the ICS a number of years ago, so "T"/"Tertiary" is no longer a recognized term. See [2] , though note that this article is itself out of date as the ICS was successfully petitioned to keep the Quaternary around. Dinoguy2 (talk) 18:05, 7 July 2015 (UTC)
The page you link to says, "It will probably be a long time (if ever) before the extinction of the dinosaurs at the Cretaceous-Tertiary (or KT) boundary becomes associated with the "Cretaceous-Paleogene (or KPg) boundary"." IUGS (which includes ICS) dropped the Tertiary period from its time scales back in 1989.[3] So what changed recently? The ICS recommended that geologists stop using the term in 2005. The ICS is entitled to its opinion, but it is not like they have jurisdiction. The U.S. Geological Survey, as well as the German and French mapping authorities, still use "Tertiary."[4] The USGS time scale is here. ("Although the Tertiary is not recognized by many international time scales, the GNC agrees that it is important that it be recognized as a system/period.") H. Humbert (talk) 03:26, 8 July 2015 (UTC)

Requested move 8 July 2015[edit]

The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review. No further edits should be made to this section.

The result of the move request was: not moved. Jenks24 (talk) 10:32, 16 July 2015 (UTC)



Cretaceous–Paleogene boundaryCretaceous–Tertiary boundary – As various comments above testify, numerous readers knowledgeable on these matters are WP:ASTONISHED by the current title of this article. Moreover, it does not appear to be supported by any category of RS. On Google scholar since 2010, I get 1,600 hits for the current form, 3,820 for the proposed form. This ngram also shows K-T dominating, although it goes up only to 2008. This article was moved in 2012 a result of this RM. The ICS recommended in 2005 that geologists stop referring to the following period as the "Tertiary." According to the logic of the previous move, this “changed the name” of the boundary. No. 1: It is quite common for geologists to use terms like "K–T boundary,” “KTB,” or “Cretaceous-Tertiary boundary” regardless of their views concerning period names. No. 2: The U.S Geological Survey and other geology heavyweights still produce time scales that feature the Tertiary, as you can see here and here. H. Humbert (talk) 16:07, 8 July 2015 (UTC)

Oppose I don't think there are dozens of confused geologists wandering around Wikipedia, struggling to find this page. I've made Cretaceous-Tertiary boundary a re-direct here just in case. Geogene (talk) 19:57, 8 July 2015 (UTC)
  • Wikipedia is not a geology encyclopedia, it is a general encyclopedia. Keep in mind WP:JARGON, WP:COMMONNAME, WP:OFFICIALNAME -- We use don't use official names because they are official, we use common names, such as those likely found in reliable sources for readerships of a general audience, not just specialist journals. Indeed, specialist journals usually represent primary sources which are not preferred, compared to secondary and tertiary sources ("tertiary source" does not mean "Tertiary period" in this sentence; but tertiary sources may use the term "Teritary" to refer to the period or they may use Paleogene). -- 67.70.32.20 (talk) 04:22, 9 July 2015 (UTC)
Oppose: As one of those old confused geologists who grew up with Tertiary, I can learn new stuff. As the Tertiary no longer exists officially, K/Pg makes sense. Geology is a dynamic science and terminology changes along with it. Anyone arguing for geosynclines? Vsmith (talk) 21:42, 8 July 2015 (UTC)
Comment. "Tertiary" lost its official status back in 1989. But continued unofficial usage didn't bother anyone, at least until recently. If the USGS thinks the period is still "important" to geologists, I assume it is. As the page cited above explains, "the map symbols “T” (Tertiary) and “Q” (Quaternary) have been used on geologic maps for more than a century and are widely used today." H. Humbert (talk) 04:20, 9 July 2015 (UTC)
This is not correct, the ICS did not formally recommend abandoning "Tertiary" as a subdivision of the Cenozoic until 2004. The USGS is different but as an international encyclopedia, the ICS terminology should be preferred. Note that the USGS and ICS give conflicting dates for all of the geological periods and we need to choose one over the other, or list both on thousands of pages that use these scales. Dinoguy2 (talk) 20:12, 9 July 2015 (UTC)
Oppose: There's a difference between being astonished by something and learning something. If users are not aware that Tertiary was abandoned a decade ago I would not describe them as knowledgable. The official publications of the ICS are a valid enough source even if not all publications have caught up. The USGS classification and terminology, as a regional organization, should not be preferred over the ICS, an international organization. Dinoguy2 (talk) 20:06, 9 July 2015 (UTC)
  • IMO, what readers are "learning" from this title is undue respect for the ICS, which I assume is made up mostly of non-English speaking countries. We should follow references intended for the English-speaking general reader, including undergraduate-level textbooks, general encyclopedias, and scientific encyclopedias. That's what our guidelines say, and any style book will give you similar advice. The top geology textbook is Understanding Earth. The 2014 edition (not online) has a “complete geologic time scale” on page 210 that features the Tertiary. As the ngram in the nomination shows, virtually no one was using the current title as recently as 2008. As for the ICS, it stopped using "Tertiary" back in 1976.[5] H. Humbert (talk) 05:16, 10 July 2015 (UTC)
Well, there are two main geological organizations in the United States, AAPG and GSA. Here is the AAPG's wiki entry for "Tertiary" [6], which says it is not the preferred term, and here is the GSA Geological Time Scale [7] which does not include Tertiary. Science has moved on. Not all textbook publishers may have contracted to have their scales re-drawn, but they're going to at least include "Tertiary" for the next 50 years or so at least merely because of the large number of old maps out there that use "Tertiary". Nothing has changed since the 2012 consensus agreed to move the page here, and I see no point in moving it back. Geogene (talk) 19:23, 10 July 2015 (UTC)
You are sourcing to a Wiki? Not only that, but the only reference it gives is the GeoWhen Data article. This article states, "it will probably be a long time before...the Cretaceous-Tertiary (or KT) boundary becomes associated with the "Cretaceous-Paleogene (or KPg) boundary"." Whether Tertiary is a period that belongs on a formal time scale is not really the issue here anyway. I noticed that Understanding Earth also has a discussion of the "Cretaceous-Tertiary impact" (p. 237), which is more directly relevant. If geology students using the latest textbooks are learning this term, that's pretty up-to-date. H. Humbert (talk) 02:23, 11 July 2015 (UTC)
Yes, in a Talk Page discussion. As I said, geology students will continue to learn the term for the next century because all the old maps call it Tertiary. That doesn't mean that geologists will be using the term in new publications for that long. Geogene (talk) 19:12, 13 July 2015 (UTC)
Oppose: Tertiary is deprecated, and that should be enough. As far as I can tell, it's not at all controversial to change the title when an organization or corporation changes it's name (and WP:ASTONISH and WP:COMMONNAME never crop up in discussions about these sorts of title change). When a person changes their name officially, it's not to controversial to change the title (but if there's no official change Wikipedia gets endless threads about their gender identity (Caitlyn Jenner) or how often they use their maiden name (Hillary Clinton) even if we eventually add up at what the person seems to prefer). Can we give science the same weight we give corporations and accept that title changes are appropriate when the authoritative sources have moved on? Plantdrew (talk)

The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page or in a move review. No further edits should be made to this section.

Explanation needed?[edit]

Someone can explain what does this excerpt mean "the earliest of which approximately separated by marl and marly 9 m (30 ft) from the K–T boundary"? The combined presence of a noun and its derived adjective is quite uncomprehensible, to me at least. Also their relation to the given linear distance is grammatically unclear. Carlotm (talk) 09:16, 19 January 2016 (UTC)

I've made some fairly sweeping changes to that section to try to make it more comprehensible. The geologists mentioned are interpreting a core sample that was left over from drilling an oil well. The distance is a vertical one, with the lowest (oldest) impact spherule layer being 9 m below the K-T boundary. One team interprets that 9 m interval to represent 300,000 years of sedimentation. If correct, that would make the Chicxulub crater older than the K-T boundary, and so not the direct cause of the extinction. This interpretation is not accepted by the larger scientific community. A marl is a muddy kind of rock made of clay and chalk. The original phrase was probably "marls and marly clays" or something like that, but I've taken that out completely because seems unimportant to the controversy. Geogene (talk) 20:47, 19 January 2016 (UTC)
Geogene I'm glad you re-worded that section. However, I think it needs a little more work to be really clear. This is the last sentence in that paragraph, the third paragraph in the Chicxulub Crater section:
  • However, Schulte and other 40 co-authors reject that the spherule is slumped from the upper spherule layer that lies on the K-T boundary. Also, Keller's conclusion is unsupported by radioisotope dating and deep-sea cores.
In the sentences immediately preceding this one, I don't see any mention of a single spherule. We do read about "impact spherules" and a "spherule layer", but not a "spherule". Also, there was no previous mention of two spherule layers, an upper one and a lower one. Before saying "the upper spherule layer" (or even "the lower spherule layer"), the fact of two layers ought to be introduced.
The sentence before that one is:
  • According to Keller's interpretation, the interval between the spherule layer and the K-T boundary represents about 300,000 years of long-term sedimentation.
I'm a little puzzled by the phrase "the spherule layer" because the previous sentence says, "This dating is based on evidence collected in Northeast Mexico, including stratigraphic layers bearing impact spherules, the earliest of which is approximately 10 m (33 ft) below the K–T boundary.
Is the phrase "the spherule layer" supposed to refer to the various "stratigraphic layers bearing impact spherules" (which would be odd, a singular phrase referring to a plural one) or to "the earliest" of those layers? If it is supposed to be referring to "the earliest" of those layers, it would be clearer to say, in the next sentence, "that earliest layer". I realize that these sentences are taken from various sources, but, with a little attention to wording, the paragraph can be made more cohesive, so each sentence has some connection to the previous one. Corinne (talk) 03:05, 20 January 2016 (UTC)
It's supposed to refer to the lowest spherule layer, which they take to have formed at the time of impact. I've implemented your suggestion. Note that the "However, Schulte and other 40 co-authors[14] reject that the spherule is slumped" looks wrong to me: it seems logical that Schulte might have argued that the beds might have slumped, and Keller would argue that they didn't. I haven't seen the Schulte paper yet so I haven't messed with that. Geogene (talk) 03:26, 20 January 2016 (UTC)