Updates to "The Age of Everything" (by Chapter)

Chapter 1: Introduction

Chapter 2: The Calendars of the Classic Maya

Added 2/1/09 In the second (2008) edition of "Chronicles of the Mayan Kings and Queens" by S. Martin and N. Grube, the authors report on a revised interpretation of of one of the events involving Yuknoom Ch'een, B'alah Chan K'awiil and Nuun Ujol Chaak. Specifically, they now state that Nuun Ujol Chaak of Tikal did not arrive in Palenque in 659 after his defeat by Calakmul. This revision is based on work by D. Stuart referenced obliquely in a chapter by S. Martin in "Tikal: Dynasties, Foreigners and Affairs of State" (2003, edited by J.A. Sabloff), which asserts that the character named "Nuun Ujol Chaak" in the Palenque inscription is denoted as the ruler of a city called the "Wa-bird polity" (located in Santa Elena, not far from Palenque) instead of Mutual/Tikal. These authors therefore argue the king mentioned in the Palenque inscription is a different king who just happened to have the same name as the ill-fated king of Tikal.

While I must defer to the experts regarding the reading of what city the Nuun Ujol Chaak in the Palenque inscription was supposed to have ruled over, I am not entirely sure I accept the idea that there just happened to be two kings named "Nuun Ujol Chaak" ruling two different cities at the same time. As Martin points out in his chapter on Tikal, the date in the Palenque inscription is exactly 1 k'atun from B'alah Chan K'awiil's final defeat of Nuun Ujol Chaak (11 Kaban 10 Sotz, note this event was not included in the appendix to Chapter 2 because the texts did not reference Yuknoom Ch'een directly). This seems to be a bit of a coincidence, and hints that the authors of either the Palenque or the Dos Pilas texts were trying to tie these two events together. This (along with the fact that Calakmul operating in nearby cities like Moral and Piedras Negras at this time) leads me to wonder if the Nuun Ujol Chaak of Santa Elena really was the same as the Nuun Ujol Chaak of Tikal. Perhaps Nuun Ujol Chaak chose Santa Elena as a base for operations when he could not rule in Tikal. Obviously, this is merely wild speculation on my part, and it is indeed possible that these coincidences in names and dates are just coincidences. Regardless, it would be very interesting to see if monuments from Santa Elena dating from this time period could shed light on this situation.

Chapter 3: Precession, Polaris and the Age of the Pyramids

Added 01/08/2010 An interesting new paper entitled "Radiocarbon-Based Chronology for Dynastic Egypt" by C.B. Ramsey and colleagues has appeared in Science (Vol 328, Page 1554-1557). This work performs a comprehensive analysis of many radiocarbon dates from throughout the Old, Middle and New Kingdoms in order to better constrain the chronology of Ancient Egypt.

Of particular interest here is that these authors find that reigns of the various Old Kingdom rulers are about a century earlier than K. Spence's model would predict. If these findings are correct, then this would certainly invalidate Spence's method of dating the pyramids. However, this analysis included only a few radiocarbon dates from the Old Kingdom (several from the reign of Djoser, one from the reign of Snofru and one from a fifth Dynastry king Djedkare). The constraints on the age of the Old Kingdom are therefore not as robust as those for the Middle and New Kingdoms, and so some caution is needed when accepting these dates. Hopefully more radiocarbon dates from the Old Kingdom, and especially the fourth dynasty, will become available in the future.

Chapter 4: The Physics of Carbon-14

Chapter 5: Calibrating Carbon-14 Dates and the History of the Air

Added 12/19/08 A nice review article has appeared on www.arxiv.org that describes how Carbon-14 and Beryllium-10 data can be used to infer changes in solar activity over the last few thousand years, complete with numerous references. The article is "A History of Solar Activity over Millennia" by I.G. Sokal www.arxiv.org/abs/0810.3872 .

Chapter 6: Carbon-14 and the Peopling of the New World

Added 07/12/08 Two papers in the 9 May 2008 issue of Science (Volume 320) describe findings relevant to the earliest inhabitants in the New World. The first, by T.D. Dillehay and colleagues (pages 784-786) is titled "Monte Verde: Seaweed, Food, Medicine , and the Peopling of South America" and it reports on samples of seaweed found at the Monte Verde site in south-central Chile. Carbon-14 dates from this material are consistent with earlier evidence indicating that this site was occupied around 14,000 years ago. In other words, these new dates continue to support the idea that people inhabited this site well before the sites containing Clovis points appeared in North America. What is perhaps more interesting, however, is the variety of different types of seaweed found at this location, which provides information about resources used by the people who lived here. For example, some of the seaweed the excavators identify as coming from the Pacific Ocean.

The other paper, by Gilbert et al. (pages 786-790) and entitled "DNA from Pre-Clovis Human Coprolites in Oregon, North America" provides information about a possibly new site where people may have lived before the appearance of Clovis points. This paper describes ancient feces from a cave in southern Oregon that contain human DNA. Carbon-14 dates of this material suggest that people were doing their business here sround 14,000 years ago. While ancient feces may not be the most glamorous thing to study, it does have the advantage that it is organic material with a fairly direct connection with human activity. This greatly reduces the number of possible ways that the dates could provide a misleading estimate of when people were in the area. Also, as a new site, it holds the promise of providing a clearer picture of what people were doing before they created Clovis points. Even so, these new findings still need to be critically evaluated and the relationships of this material to other remains in the area still needs to be researched before the implications of these early dates can be completely understood. (For the masochistic, some technical arguments about the finer points of this analysis appeared in the 10 July 2009 issue of Science, Vol 325, pg 148a-d.)

Added 12/27/08 Another interesting paper on the earliest inhabitants of the New World has been published in the journal American Antiquity (Vol 73(4) 2008, pp 670-698): "Archaeological roots of human diversity in the New World: A compilation of accurate and precise radiocarbon ages from earliest sites" by M.K. Faught. Like the works by Roosevelt et al. and Waters and Stafford referenced in the book, this paper describes a compilation of carbon-14 dates from the earliest known sites from the Americas. Comparing the best-dated sites from all over North and South America, this author demonstrates that there are a few sites found at widely separated locations around the New World before 11,000 years ago, followed by a much greater number of sites in several different regions after 11,000 years ago. The author of this article points out that the rapid incrase in the number of sites occurs at nearly the same time in North and South America, which is difficult to reconcile with an wave of immigrants from the North. He suggests that instead of a wave of people moving through the ice-free corridor into the Americas at the end of the last ice age, the increase in the number of sites found after 11,000 years ago may reflect the dispersal of people away from the coasts prompted by changes in sea levels associated with the end of the Ice Age. This would imply that both the east and west coasts of North America and the western coast of South America were already inhabited before 11,000 years ago. Of course, the details of that early occupation is still unclear.

Added 4/29/11: A very interesting paper has recently been published on pages 1599-1603 in Volume 331 of the Journal Science (2011). This paper, entitled "The Buttermilk Creek Complex and the Origins of Clovis at the Debra L. Friedkin Site, Texas" by M.R. Waters and collaborators, describes a site that provides some of the best evidence yet for a pre-Clovis occupation in North America. This site preserves a very clear sequence of lithic artifacts in a series of strata dating back a couple of thousand years before the Clovis era. These strata are nicely layered and have been dated, not by radiocarbon methods, but instead by optically-stimulated luminesence methods. These dates form a coherent sequence and thus seem robust, but what makes the site particularly interesting is that it preserves multiple stone tools that seem to redate to distinctive Clovis artifacts. This site thus provides an opportunity to better understand what artifacts might be used to identify other potential pre-Clovis occupations.

Added 01/07/12 Another bit of information about pre-Clovis people in North America has been published in the paper "Pre-Clovis Mastodon Hunting 13,800 Years Age at the Manis Site, Washington" by M.R. Waters et al. (Science, 334, 351-353, 2011). This paper describes a stone point lodged in a Mastadon bone that dates back about 1000 years before people started making Clovis points.

Chapter 7: Potassium, Argon, DNA and Walking Upright

Added 03/29/08: A couple of interesting papers on early ancestors of humans have appeared recently. First, on page 1662-1664 of volume 319 of Science there is an article "Orrorin tugenensis Femoral Morphology and the Evolution of Hominin Bipedalism" by W.F. Richmond and W.L.Jungers. This paper analyzes a 6-million-year-old femur (leg bone) belonging to an early hominid named Orrorin tugenensis and compares measurements of this bone with those of humans, hominids and other great apes. This analysis indicates that Orrorin was bipedal, which if correct would imply our ancestors first began to walk upright at least 6 million years ago.

Another interesting paper by A.-E. Lebatard and colleagues entitled "Cosmogenic nuclide dating of Sahelanthropus tchadensis and Australopithecus bahrelghazali: Mio-Pliocene hominids from Chad" has appeared in The Proceedings of the National Academy of Science (Volume 105, pages 3226-3231). This article describes efforts to date the early hominid fossils found in Chad. As mentioned in the book, these fossils cannot be dated directly with Potassium-Argon techniques because this region does not contain the right sorts of volcanic deposits. The authors of this paper therefore turned to another unstable nuclei, Beryllium-10, which is created in the atmosphere by cosmic rays much like Carbon-14. Unlike Carbon-14 atoms, however, Beryllium-10 atoms do not remain in the atmosphere as part of gas molecules, but instead fall to earth in rain and collect in lakes, etc. The sedimentary deposits laid down in the bottom of lakes therefore contain some Beryllium-10 when they form, which then steadily decays away with a half-life of about 1.4 million years. As with any other method of measuring age with unstable nuclei, the trick is to estimate how much Beryllium-10 these deposits contained originally, which is especially challenging because the total Beryllium content of a lake includes material extracted from local rocks, so the original Beryllium-10 content of a deposit (relative to other isotopes of Beryllium) can vary from place to place. The authors of this study deal with this issue by comparing the Beryllium-10 content of the fossil-bearing deposits with those from the same region, which is a large basin centered on Lake Chad.

The authors find that the ages they estimate for various deposits in this region match those derived based on the types of fossil animals found in the different layers of rock. In particular, they find that the deposits containing the early hominid Sahelanthropus tchadensis are about 7 million years old, confirming the previous dates based on the presence of certain fossil animals. These new dates therefore can provide some additional support to the great age of these fossils, and their importance in understanding the origins of bipedalism.

Added 10/16/09 An extremely important series of papers have appeared in the 10/02/09 issue of Science (available here). These papers describe in detail a fossil hominid Ardipithecus ramidus found in Ethiopian deposits dating back to about 4.4 million years ago. The age of the fossils is well established by virtue of being sandwiched between two volcanic deposits that can be dated with the Potassium-Argon system. These fossils are not as old as the Sahelanthropus and Orrorin finds, but they are nevertheless signficant because they include many bones of a single individual, including parts of the hands, feet and pelvis. This is therefore the oldest fossil hominid specimen that is complete enough to provide a reasonable picture of how it moved around, and therefore can potentially shed important new light on the origin of our peculiar form of bipedalism.

While Ardipithecus has some characteristics in its pelvis and feet which indicate that it could walk on two legs, it does not appear to have all the characters of later hominids that make them efficient bipedal walkers. Furthermore, some characteristics of Ardipithecus, such as a big toe that is out of alignment with the rest of the foot, indicate that it retained adaptations for clambering through trees. Also of interest is the fact that the hands and feet of Ardipithecus do not show adaptations for vertical climbing or knuckle-walking found in modern chimpanzees. This suggests that the ancestors of chimpanzees acquired these traits sometime after they split off from the ancestors of modern humans, while our ancestors retain a more generalized anatomy suitable for clambering on branches until they developed the ability to walk upright. These findings certainly cast important new light on the origin of bipedalism.

Of special relevance to the discussion in the book is a comment made by White et al. on page 81. Here the authors call into question the estimated age of the split between the ancestors of modern Chimpanzees and the ancestors of modern Humans. They argue that many characters shared by gorillas and chimpanzees (such as knuckle walking) are not found in Ardipithecus, so these animals probably differ more from the last common ancestor of chimpanzees, gorillas and humans than was previously appreciated. They then suggest that this could mean that more time might be neccesary from the different groups to acquire their unique characters. While I agree with the first point, I think the second is rather questionable. If there was clear evidence for knuckle-walking chimpanzee-ancestors from 6 million years ago, then there might be reason to question the age estimates derived from molecualr analyses, but at present the fossil record of the ancestors of chimpanzees and gorillas is so sparse that I cannot see any way to make any sensible argument about how long it should have taken the ancestors of chimpanzees or gorillas to acquire their unique traits. It seems to me that the Ardipithecus findings simply emphasize that we need information about both our unique ancestors and the ancestors of our nearest relatives, the chimpanzees and gorillas to clarify the history of bipedalism. Only by comparing the trends and traits among these different lineages will we be able to fully understand the particular circumstances that led to our unique mode of locomotion.

Added 8/18/12: An interesting analysis of divergence times between the ancestors of humans and great apes has recently appeared in the Proceedings of National Academy of Science. K.E. Langegraber and coleagues' article "Generation times in wild chimpanzees and gorilla suggest earlier diverge times in great ape and human evolution" describes an effort to compute divergence times independent of any fossil information. In essence, they use the number of mutations found between generations in humans and new estimates of generation times in great apes to estimate how much time would be needed for chimps and humans to have the number of genetic differences observed today. These calculations inidcate that humans and chimpanzees last shared a common ancestor between 7 and 13 million years ago. These are quite a bit older than the 4-6 million year estimates of previous studies, and might have implications for the interpretation of some of the early hominid fossils like Orrorrin, Ardipithecus and Sahelanthropus /

Chapter 8: Molecular Dating and the Many Types of Modern Mammals

Added 11/03/07: There have been a number of interesting papers published recently using new gene sequence data to examine and refine the relationships between the different orders of placental mammals. These papers, instead of looking at the point substitution mutations discussed in the book, focus on insertions and deletions of short stretches of DNA. These sorts of mutations are relatively rare and are less likely to occur multiple times, so they can potentially help resolve some of the relationships among mammalian orders.

Two recent analyses suggest slight re-arrangements of the relationships shown in Figure 8.3 of the book. One study finds that within Laurasiatheria, the animals in the orders Carnivora (and presumably Pholidota), Chiroptera and Perrisodactyla are more closely related to each other than any of them is to animals in the orders Cetacea or Artiodactlya (see "Pegasoferae, an unexpected mammalian clade revealed by tracking ancient retroposon insertions" by Nisihara et al. in Proceedings and of the National Academy of Sciences Volume 103 (2006), pages 9929-9934.) Another analysis finds that Dermopterans or Flying Lemurs are more closely related to Primates than to Scandentians or Tree Shrews (see "Molecular and Genomic Data Identify the Closest Living relative of Primates" by Janecka et al. in Science Volume 792 (2007), page 792-794.)

At a more fundamental level, another recent paper provides genetic data suggesting that Xenarthrans may be more closely related to Afrotherians than to Euarchontoglires or Laurasiatherians (see "Using genomic data to unravel the root of placental mammal phylogeny" by Murphy et al. in Genome Research Volume 17 (2007) pages 413-421. If correct, these findings could bring the the picture of mammal migrations inferred from the genetic data more in line with the fossil evidence. If Xenarthrans and Afrotherians are more closely related to each other than either one is to Euarchontoglires or Laurasiatherians, this might mean that one group of early eutherians from the northern continents moved into the southern hemisphere to become the ancestors of Afrotherians and Xenarthrans, while another group remained in the northern hemisphere and formed the ancestors of Euarchonotoglires and Laurasiatherians.

One challenge presented by these new findings is that because the insertion or deletion of DNA sequences is comparatively rare, only a small number of these mutations identify any given group. These mutations therefore cannot themselves provide estimates of when these various groups diverged. Age estimates therefore still must be derived from the point substitution mutation data. Since analyses of these data favor somewhat different groupings of the orders, there are clearly some issues with the reliability of such dates. Future research should help clarify this situation and help resolve whether any of these seeming inconsistencies are merely due to the limited number of organisms studied thus far.

Chapter 9: Meteorites and the Age of the Solar System

Added 09/06/09 A recent paper has come out that lends further support to the idea that the short-lived radioactive nuclei like Aluminum-26 was distrubted uniformly in the early Solar System and thus can be used to date events from that time. The paper is called "Homogeneous Distribution of 26Al in the Solar System from the Mg Isotopic Composition of Chondrules" by J. Villeneuve, M. Chaussidon and G. Libourel in Science Volume 325, pg 985-988. In it, the authors, provide evidence that objects which formed with a lower fraction of Aluminum-26 also initially had a higher initial concentration of Magnesium-26. This is what one would expect if Aluminum-26 was introduced into the Solar System in a single burst, and as time went on, that Aluminum-26 steadily decayed away to produce more and more Magnesium-26. The authors also provide new evidence that the Chondrules in a particular Chondritic meteorite solidified over a time-span of a couple of million years.

Added 05/20/10 A paper has now appeared in the journal Science ("238U/235U Variations in Meteorites: Extant 247Cm and Implications for Pb-Pb Dating" by Brennecka et al. Volume 327, pages 449-451 (2010))that reveals some new complications for efforts to accurately date meteoritic material using the decay of various isotopes of Uranium into Lead. Normally, this technique assumes that all materials have the same ratio of Uranium isotopes. However, these researchers have found that the ratio of Uranium-238 to Uranium-235 can in fact vary by 0.3% in various parts of certain meteorites. Much of these variations in the Uranium isotope ratio seem to be correlated with the abundance of elements like Thorium and Neodymium. Just as the correlation between the variations in Magnesium isotope ratios and the amount of Aluminum in different parts of meteorites imply that the meteorite originally contained some short-lived isotopes like Aluminum-26 that decayed long ago. In this case the most likely explanation for these variations is that the meteorites that now contain more Thorium and Neodynium also contained more short-lived isotopes of Curium, which has similar chemical properties. This Curium then decayed to produce excess Uranium-235. This excess Uranium-235 can affect the dates derived from Uranium-Lead by a few million years. Given these rocks are 4.5 billion years old, this is not a big affect, but it is important in efforts to measure small differences in ages between CAIs, chondrules and other components of meteorites.

Chapter 10: Colors, Brightness and the Age of Stars

Added 07/12/08 I recently became aware of another paper that discusses the implications of the new measurements of nuclear reactionrates on the age of globular clusters. This article is by Degl'Innocenti et al. and is published in Physics Letters B 590 (2004) 13-20.

Added 01/10/08 A brief review article has appeared in Science that cites various methods for measuring the age of stars (and provides some useful references). It is "How Old Is That Star?" By D.R. Soderblom in Science, Vol 323 (2009) pg 45-46.

Chapter 11: Distances, Redshifts and the Age of the Universe

Added 03/29/08 New measurements of 60 Type Ia Supernovae and their implications for the composition of the universe are described in three papers in volume 666 of the The Astrophysical Journal , pages 674-725 by Miknaitis et al., Wood-Vasey et al. and Davis et al. These additional continue to support the idea that the present-day universe on average contains about three parts Dark Energy for every one part matter, and that the Dark Energy can be treated as a cosmological constant.

Added 05/20/10 A good review of efforts to measure the Hubble constant by W.L. Freedman and B.F. Madore (Annual Review of Astronomy and Astrophysics, Vol 48, arXiv:1004.1856). These measurements provide information about the distances to various galaxies which are essential to determine the expansion history of the universe.

Chapter 12: Parameterizing the Age of the Universe

Added 03/09/08: New data on the brightness variations in the Cosmic Microwave Background (CMB) have recently appeared on-line. High-resolution measurements from an earth-based instrument known as ACBAR can now be found here , and a series of papers describing the latest results from the WMAP spacecraft can be found here . The WMAP papers include refined measurements of many cosmological parameters, including the curvature and the age of the universe, as well as comparisons with other astronomical measurements. All these data still indicate that the universe is close to flat, and if flat is about 13.7 billion years old.

It is interesting to note that in some of these recent papers the authors state that the CMB data alone cannot provide tight constraints on the curvature of the universe (see the paper by Komatsu et al., for example). By contrast, I describe in Chapter 12 how the patterns in the CMB can provide us with a pretty good measure of the curvature and the total energy density in the universe. This is not so much a contradiction as much as a measure of how far cosmology has come over the last few years in determining the structure and composition of the universe. As I discussed in the book, the apparent size of structures in the CMB is most sensitive to the overall curvature of the universe. However, it is also true that these measurements can also be affected somewhat by the composition of the universe (which can change the expansion history). This places limits on how precisely cosmologists can measure the curvature with CMB data alone. With the increasing precision of the various data sets, cosmologists are not satisfied with these limits and so are using data from other observations (like supernovae) to constrain the composition and structure of the universe and refine their estimates of parameters like the curvature or age of the universe.