The Ediacara biota are a now extinct group of soft-bodied animals that lived in deep water environments at the end of the Neoproterozoic era (1,000 to 542 million years ago). Modified from Narbone, 2005.
However, molecular clock studies estimate the divergence of the metazoan lineage to have occurred as long as 1,400 million years ago (Skorokhod et al., 1999). Therefore, there should be a long history of animal life that preceded the rise of the Ediacara biota.
Calcarea, Demospongiae, and Hexactinellida sponges are the basal metazoans and are estimated to have diverged from the last common metazoan ancestor between 1,100 million years ago and 1,400 million years ago. Modified from Skorokhod et al., 1999.
Until recently however, definitive evidence for animals before 580 million years ago has been lacking. A 2009 study that analyzed molecular fossils (biomarkers) from the Huqf Supergroup in South Oman, identified a biomarker indicative of marine sponges (sponges are at the base of the animal tree of life). The biomarker, 24-isopropylcholestane, was identified throughout the Huqf Supergroup which ranges in age from more than 635 million years old at the base to less than 541 million years old at the top of the section (Love et al., 2009).
The stratigraphic distribution of samples containing the 24-isopropylcholestane biomarker are plotted on the right. Absolute age constraints that were measured from U-Pb of detrital zircons and ash within the Huqf group are shown in black and absolute age constraints based on stratigraphic correlation with other dated units are shown in red. Modified from Love et al., 2009.
This is significant not only because it pushes back the animal fossil record by more than 30 million years but it also suggests that the dissolved oxygen concentration, at least in the shallow ocean, was high enough to support animal life.
If you would like to learn more please read the original paper Love et al., 2009
References:
Love, G.D., Grosjean, E., Stalvies, C., Fike, D.A., Grotzinger, J.P., Bradley, A.S., Kelly, A.E., Bhatia, M., Meredith, W., Snape, C.E., Bowring, S.A., Condon, D.J., Summons, R.E. (2009). Nature, vol. 457, p. 718.
Narbone, G.M. (2005). Annual Review of Earth and Planetary Science, vol. 33, p. 421.
Skorokhod, A., Gamulin, V., Gundacker, D., Kavsan, V., Müller, I.M., Müller, W.E.G. (1999). Biological Bulletin, vol. 197, p. 198.
I think this post was fairly easy to follow along with regardless of audience background. The relevance of the research is explicitly stated, which is helpful for the reader as it provides focus and direction for the content early on. It is also an interesting topic. I think a small description of what a biomarker is(in general and also this specific one) might be helpful for the general audience. Otherwise, nicely done.
ReplyDeleteCouple comments on this, overall I really enjoyed your post.
ReplyDelete-Great title, intriguing, easy to understand, draws the reader in
-Nice job linking potentially confusing terms (ediacara biota, morphologically, etc)
-Good fossil pictures, but perhaps a picture of a modern relative of the sponge in question, or of your field work to give the reader more of a point to connect with
Also, you mentioned that the biomarker is "indicative of marine sponges". Out of curiosity, if only indicative, what is the potential error here? IE, what could produce a "false positive"?
This post is well-written, informative, and easy to follow. A lot of the 'jargon' is defined well, and the Wikipedia links are well-placed. The only thing that is missing is a sense of the scale of these animals in the first photo.
ReplyDeleteI really like the logical flow of this post. You work through the scientific thought process in an understandable way. However, I don't think your second picture helps to get your point across or make it more interesting. Maybe you could include a picture of modern sponges along with it or instead of it to emphasize their simple morphology.
ReplyDeleteThe inclusion of explanatory links was particularly helpful, and a touch that I may have to emulate. The article was perfectly suited to a general audience, in no small part because of the ability of the reader to catch up as the post is read.
ReplyDeleteA very informative post in a clear language, which makes it easy to follow. Although I think it is not necessary to mention the specific name of the biomarker, the article is far from being overloaded with technical terms.
ReplyDeleteI particularly like the picture with the fossil compilation at the beginning of the text, which catches the reader and makes the topic more "tangible" for a general audience.
Very good post. The title works good to catch attention, and I like the citations. I also really like how you provide links for all the harder terms given.
ReplyDeleteWow, this was an excellent post. The links were great, and are really helpful. I really like the way you structured the post, and the way you explained the concepts. The figures were well chosen and illustrated your point. Pushing the animal fossil record back 30 mya is a big deal, so I like your choice in post topic. You may want to include your findings somewhere in the beginning of the post to allow readers to understand where you are going with it from the beginning.
ReplyDeleteThis post is really interesting. other evidence is found to support the timing of animal evolution, although how robust it is for this method beyond my knowledge to evaluate.
ReplyDeleteI would like to look at the paper by love 2009, to see if I can find more information helpful.
This is the best title out of all the posts, and a really interesting topic. I think it might be nice to talk a little about what kinds of chemical compounds can survive so long in rocks, and how we know they are indicative of specific precursors. This is the sort of question lay readers don't even think to ask, and it's a question with interesting answers.
ReplyDeleteVery catchy title - draws people in right away. Good flow of background information and current research. Some technical words used that can probably be replaced or just left out. I really like your closing sentence, it really emphasizes the significance of the work. The first image is really good, the second two are a bit blurry and I'm not sure many people would understand how to interpret a strat column. Overall, good blog.
ReplyDelete