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
9.12.6.16.17 (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.