The composition of the Earth

Approximation of terrestrial lead isotope evolution by a two-stage model

[1] We present a 53-Myr stack (the “LR04” stack) of benthic δ18O records from 57 globally distributed sites aligned by an automated graphic correlation algorithm This is the first benthic δ18O stack composed of more than three records to extend beyond 850 ka, and we use its improved signal quality to identify 24 new marine isotope stages in the early Pliocene We also present a new LR04 age model for the Pliocene-Pleistocene derived from tuning the δ18O stack to a simple ice model based on 21 June insolation at 65°N Stacked sedimentation rates provide additional age model constraints to prevent overtuning Despite a conservative tuning strategy, the LR04 benthic stack exhibits significant coherency with insolation in the obliquity band throughout the entire 53 Myr and in the precession band for more than half of the record The LR04 stack contains significantly more variance in benthic δ18O than previously published stacks of the late Pleistocene as the result of higher-resolution records, a better alignment technique, and a greater percentage of records from the Atlantic Finally, the relative phases of the stack's 41- and 23-kyr components suggest that the precession component of δ18O from 27–16 Ma is primarily a deep-water temperature signal and that the phase of δ18O precession response changed suddenly at 16 Ma

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A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records

Coral reefs drilled offshore of Barbados provide the first continuous and detailed record of sea level change during the last deglaciation. The sea level was 121 ± 5 metres below present level during the last glacial maximum. The deglacial sea level rise was not monotonic; rather, it was marked by two intervals of rapid rise. Varying rates of melt-water discharge to the North Atlantic surface ocean dramatically affected North Atlantic deep-water production and oceanic oxygen isotope chemistry. A global oxygen isotope record for ocean water has been calculated from the Barbados sea level curve, allowing separation of the ice volume component common to all oxygen isotope records measured in deep-sea cores.

A 17,000-year glacio-eustatic sea level record: influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation

Solar photospheric and meteoritic CI chondrite abundance determinations for all elements are summarized and the best currently available photospheric abundances are selected. The meteoritic and solar abundances of a few elements (e.g., noble gases, beryllium, boron, phosphorous, sulfur) are discussed in detail. The photospheric abundances give mass fractions of hydrogen (X ¼ 0:7491), helium (Y ¼ 0:2377), and heavy elements (Z ¼ 0:0133), leading to Z=X ¼ 0:0177, which is lower than the widely used Z=X ¼ 0:0245 from previous compilations. Recent results from standard solar models considering helium and heavy-element settling imply that photospheric abundances and mass fractions are not equal to protosolar abundances (representative of solar system abundances). Protosolar elemental and isotopic abundances are derived from photospheric abundances by considering settling effects. Derived protosolar mass fractions are X0 ¼ 0:7110, Y0 ¼ 0:2741, and Z0 ¼ 0:0149. The solar system and photospheric abundance tables are used to compute self-consistent sets of condensation temperatures for all elements. Subject headings: astrochemistry — meteors, meteoroids — solar system: formation — Sun: abundances — Sun: photosphere

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Solar System Abundances and Condensation Temperatures of the Elements

Sm-Nd isotopic evolution of chondrites

▪ Abstract We present a review of nucleosynthesis in AGB stars outlining the development of theoretical models and their relationship to observations. We focus on the new high resolution codes with...

/pdf/nucleosynthesis-in-asymptotic-giant-branch-stars-relevance-1594it3sxd.pdf

Nucleosynthesis in asymptotic giant branch stars: Relevance for galactic enrichment and solar system formation

^(147)Sm ɑ-decays to ^(143)Nd so that ^(143)Nd/^(144)Nd reflects the
time-integrated Sm/Nd environment of a sample. The increase
in 143/144 in a reservoir with chondritic Sm/Nd is
1.2% in 4.5AE. There exists sufficient variation of Sm/Nd to
cause sizeable effects in 143/144. Young samples were
measured to elucidate the nature of their source regions. An
oceanic high Fe, Ti basalt (113152) and alk. basalt (113031), a continental alk. besalt (BCR-l), an apatite (Khibiny massif) and two reagent "normals", NN1 and NN2, were analyzed. Isotopic ratios of NN2 and BCR-1, normalized to 148/144=0.241572 are tabulated. Following the pioneering
work of Lugmair, et al. (EPSL 27, 79) our 143/144 data are
presented relative to the total rock value for Juvinas
(0.51278). the present value of a chondritic reservoir. Data
are given as deviations from this value in parts in 10^4 (є)
and show a wide range. Nd in the source regions of the rock
samples evolved in an environment of approximately chondritic Sm/Nd (±5%) over the history of the earth. Small
variations exist, reflecting long time scale differences of
Sm/Nd in the source regions. The low Sm/Nd observed in
alkali basalts cannot reflect an ancient source region with
low Sm/Nd as є is near zero. REE patterns of alkali basalts
must thus reflect relatively recent fractionation from a
source with essentially chondritic relative abundances.
Study of initial ^(143)Nd/^(144)Nd in conjunction with REE patterns promises to contribute important petrogenetic information.

/pdf/nd-isotopic-variations-and-petrogenetic-models-32156m6uzg.pdf

G. J. Wasserburg

Papers

Sm-Nd isotopic evolution of chondrites

Nucleosynthesis in asymptotic giant branch stars: Relevance for galactic enrichment and solar system formation

Nd isotopic variations and petrogenetic models

238U234U230Th232Th systematics and the precise measurement of time over the past 500,000 years

U-Th-Pb systematics in three Apollo 14 basalts and the problem of initial Pb in lunar rocks