Department of Earth Sciences Boston University
Redefining the composition of the Earth: Implications for global geodynamics In the beginning. Courtesy of NASA/JPL-Caltech Matt Jackson Department of Earth Sciences Boston University Where is home? Following accretion, a deep terrestrial magma ocean
Siderophile elements (Fe-Ni) to the core, leaving behind the early (primitive) silicate mantle. From the primitive silicate earth, the crust (continental and oceanic) was extracted from the early primitive mantle. Crust subducted back into the mantle & mixed/stirred. Did portions of the earliest primitive mantle survive to the present day? The kinetic energy of in-falling objects was converted to heat upon collision, and the integrated heat of the collisions resulted in a molten Earth Courtesy of NASA/JPL-Caltech 2001 Brooks/Cole Publishing/ITP Brandenburg et al., EPSL 2008 Implications from Neodymium-142
Discovery:Boyet and Carlson (2005) found that 142Nd/144Nd ratios in accessible modern terrestrial lavas are 185 ppm higher than O and C chondrites. - Background:Nd-isotopes, two clocks: 147Sm decays to 143Nd (t1/2=106 Ga) 146Sm decays to 142Nd (t1/2=103 Ma) - Implications: 142Nd variation due to incomplete mixing of s-, r-process nucleosynthetic products. 142Nd variation has nothing to due with 146Sm decay. OR. Nd variation due to 146Sm decay. All modern terrestrial samples evolved from a mantle reservoir with a Sm/Nd ratio ~6% higher than chondrites. Its worth exploring the implications! - What does this mean for 143Nd/144Nd of the Earth? Baffin lavas (de Leeuw et al., 2010) In 2005, a possible solution to this paradox of non-chondritic Nd and primitive He was found. If 146Sm was 5% higher, then 147Sm was 5% higher. ---With r and s, there are predictable anomalies that we would see in other isotopes. (Boyet and Carlson, Science, 2005) There are two models for this: (Earth is not chondritic)
6% diff. +7 -units New Earth model (Earth is not chondritic) 1.Earth has higher 142Nd/144Nd thanchondrites. Therefore, accessible Earth has Sm/Nd 6% higher than chondrites. Therefore, Earths 143Nd/144Nd is higher than chondritic. 6% diff. 18 ppm 6% diff. +7 -units Reservoir parental to modern terrestrial mantle
Predicted parental mantle reservoir overlaps with high 3He/4He reservoir Reservoir parental to modern terrestrial mantle (Ra) primordial chondrite reservoir The predicted 143Nd/144Nd of the reservoir parental to modern terrestrial lavas overlaps with the 143Nd/144Nd of the highest 3He/4He lavas. Jackson et al. (EPSL, 2007) Baffin and W. Greenland picrites plot near the Geochron
Jackson et al. (Nature, 2010) Lavas overlap with the geochron. David Grahams lavas from West Greenland also overlap with the geochron. High 3He/4He lavas from other localities are shifted to the right of the geochron. Primitive Material in LLSVPs?
Global? Primitive Material in LLSVPs? Baffin Island is a flood basalt. Do other flood basalts have similar geochem signatures? Torsvik et al. (Nature, 2010) Jackson and Carlson (Nature, 2011) Trace element composition
Non-chondritic Primitive Mantle (this study) Jackson and Jellinek, in prep Non-chondritic Primitive Mantle (C&B, 2008) 13TW of radiogenic heat (instead of 20 TW) Urey ratio is a lot lower ( convective Urey ratio). To generate the continents, >70% of the mantle must be depleted. DMM must be much larger in a non-chondritic world. Is the deep, primitive reservoir hosted in the LLSVPs?
142Nd/144Nd evidence is consistent with a non-chondritic bulk earth with a 143Nd/144Nd of ! Implications for the origin of the high 3He/4He mantle reservoir.PRIMITIVE? Do flood basalts and oceanic plateaus sample a PRIMITIVE reservoir in the deep mantle? Is the deep, primitive reservoir hosted in the LLSVPs? Non-chondritic BSE (PREMA) C FOZO Early Earth & long-term evolution:Themes perfectly suited for a CIDER interdisciplinary approach.
Geochemical evolution of a non-chondritic Earth:Continents, DMM, the mantle zoo.reservoirs once considered depleted are now enriched!This is more than just 20 ppm in 142Nd/144Nd! Coupled chemical and thermal evolution of new compositional Earth models:Dynamicists, geochemists, seismologists. How to generate a non-chondritic Earth?Early differentiation, impact erosion, hidden enriched reservoirs, etc.? Seismologists.How will this affect PREM?Extract a bit of melt, look at how seismic structure changes? Composition of high 3He/4He (primitive?) mantle useful for modeling seismic properties of LLSVPs?Superplume theme? CIDER approach: -A week or two of lectures, followed by break-out groups that develop ideas organically. Maybe let this work a bit more organically than in past years?Smaller groups? AGU workshops to follow-up on collaborations? new activities beyond the summer program. What worked for you or did not work as a member of a CIDER research group? Ideas for summer program themes- How can we stimulate and support continuation of research projects after the end of the summer program.? Topics for CIDER working groups- What should a CIDER e-book contain? How do we organize and maintain it? Dear Matt,As the time of the upcoming CIDER post-AGU workshop is approaching,here are some details about the workshop and the afternoon session.We will start at 9 am and finish at 5pm.As you know, the goal of this workshop is to "kick-off" CIDER2 as anFESD "Synthesis Center" -The morning session , 9am pm features 4 plenary talks, 2 short"working group ideas" talks and ample discussion time.Lunch break from 12:30 to 2pm.2-4pm: short presentations and questions/discussion.4-5pm: general discussion and planningDuring the afternoon session, we want to stimulate discussion andideas about CIDER activities, and Because we want to privilege discussion time, please prepare no morethan 5-6 slides, and if you can come up with a title now, please sendit to me at your earliest convenience so I can post it on the web. Weare aiming at ~10 mn presentations (including questions).Looking forward to hearing from you and see you soonRegards Gannoun et al., PNAS 2011 How did the Earth get higher Sm/Nd than chondrites?
143Nd/144Nd= (143Nd=+7) Depleted accessible mantle:142Nd/144Nd requires this is source of all modern mantle reservoirs Hidden early enriched reservoir Chondritic reservoir Early differentiation (melting) event Age (Ga) **We dont know whether elevated 142Nd/144Nd in modern terrestrial rocks results from early depletion event or accretion from a non-chondritic material. Problem:Terrestrial lavas with high 3He/4He dont plot on the Geochron!
After Jackson et al. (EPSL, 2007) Samoa Galapagos Iceland Hawaii Highest 3He/4He Baffin Island lavas bracket the OJP
Jackson and Carlson (Nature, 2011) Relationship between flood basalts and a primitive (non-chondritic) mantle
Relics of the early Earth may not be so rare? Why would this reservoir be sampled by large igneous provinces? Primitive Mantle produces more heat, melts more. Primitive Mantle is more fusible, melts more. A recipe for producing extraordinary volumes of melt? Old Reservoir, Old Idea (new possibilities)
The nominal value of CHUR0 for the continental flood basalts indicates they are derived from a reservoir which has maintained an unfractionated, chondritic Sm/Nd throughout the history of the earth. -DePaolo & Wasserburg, GRL 1976 PREMA? (Prevalent Mantle)
PREMA defined by the most frequently occuring 143Nd/144Nd in global OIB dataset. Zindler and Hart (1986) PREMA is isotopically similar to the highest 3He/4He lavas. Is PREMA a surviving portion of a non-chondritic Primitive Mantle? Does PREMA source flood basalts? chondrite Range for non-chondritic primitive mantle predicted by 142Nd/144Nd Zindler and Hart, 1986 Zindler and Hart (1986): CFBs converge on PREMA Primitive Material in LLSVPs? Most models for this primitive mantle are based on the assumption that it should have relative abundances of refractory lithophile elements similar to those of carbonaceous chondrites the presumed building blocks of Earth Prospecting for primitive mantle: If any of the early-Earth survived, what would it look like today? Noble gas isotopes and abundances (high 3He/4He) A primitive, mantle reservoir should have predictable abundances (chondritic?) of the refractory, lithophile elements (e.g., Sm and Nd). 3.Pb-isotopes will be on the Geochron, the locus of data in Pb-isotope space that have had the same U/Pb for ~4.5 Ga. Any mantle-derived melts satisfying these three requirements?No! Sm-Nd and Nd-isotopes. House of cards? In the beginning. Solar Nebula Theory: Cloud of gas and dust
Courtesy of NASA/JPL-Caltech 4.568 Ga (Bouvier & Wadhwa, 2010) Solar Nebula Theory: Cloud of gas and dust Rotating disk Gravitational collapse Solar nebula with young sun Planets accrete from rotating cloud Survival of early-Earth reservoirs in a chaotic mantle?
Davies, 2002 Brandenburg et al. (EPSL 2008) Starting composition of the EarthChondritic?
1.) Carbonaceous (C) chondrites Sun 2.) C-chondrites and Earth came from the same (homogeneous?) solar nebula, and the sun represents over 99.9% of solar systems mass. 3.)Therefore, C-chondrites Earth (non-volatile, lithophile elements like Sm and Nd) 4.)If the Earth is a C-chondrite, then Earth and chondrites have the same 143Nd/144Nd.(147Sm 143Nd + 4He) This is a log-log plot covering 10 orders of magnitude! Comparison of solar-system abundances (relative to silicon) determined by solar spectroscopy and by analysis of carbonaceous chondrites (after Ringwood, 1979) Caro et al, 2008 Nature [chondrite] has been considered to define the composition of the Solar System, Primordial helium in Earths mantle?
Helium in the Earths mantle: -Two isotopes:3He (lower abundance) and 4He (greater abundance) -U and Th decay to Pb via alpha decay (4He nuclei production) -Little 3He produced in the earth (mostly primordial) -Therefore, 3He/4He in the earth decreases with time. -Absolute 3He/4He ratios in the solar system are small (10-3 to 10-8),so we normalize to 3He/4He ratio in atmosphere (Ra, 1.38x10-6). The sun (solar wind) and the atmosphere of Jupiter have high 3He/4He.High 3He/4He is thought to be primordial. Lavas with primordial 3He/4He dont have primitive chondritic 143Nd/144Nd
Enriched Depleted (Ra) primitive chondrite reservoir -Mention that this is global OIB compilation representing 30 years of work by the community; The highest 3He/4He lavas are shifted away from chondrite. -This has plagued geochemists for years.Why are primitive 3He/4He associated with distinctly non-primitive Nd?! -The atmosphere of Jupiter (Galileo probe) is 120Ra.The solar wind is ~310 Ra. MORB (depleted).CC (enriched). Jackson et al. (EPSL, 2007) Problem:Terrestrial lavas with high 3He/4He dont plot on the Geochron!
After Jackson et al. (EPSL, 2007) Samoa Galapagos Iceland Hawaii Baffin and West Greenland picrites plot near the Geochron
Jackson et al. (Nature, 2010) Lavas overlap with the geochron. David Grahams lavas from West Greenland also overlap with the geochron. High 3He/4He lavas from other localities are shifted to the right of the geochron. How does a portion of the mantle survive for ~4.5 Ga?
JP wrote: Good to hear from you: I hope everything is well in DC.Take a>> look at Fig.14 in our 2008 EPSL paper - the 5% to 7% EED models are>> the most reasonable.In these results, about 10 to 15% of the mantle>> has never been processed.However, that fraction is going to be>> widely distributed rather than in any coherent reservoir.This may be>> on the high side since we don't have compressibility / phase changes>> (read: more sluggish lower mantle)..Peter is working on that. How does a portion of the mantle survive for ~4.5 Ga? Solid-state convective stirring is thought to process large portions of the mantle on geologic time-scales. Recent dynamic models suggest that pristine portions (up to 10-15%) of the mantle might have escaped differentiation and mixing over the age of the Earth (in convective eddies?). Collaborate with dynamicists to understand nature and distribution of ancient reservoirs and how they might survive. Brandenburg et al. (EPSL, 2008) A growing clamor. Bottom line:Terrestrial oxygen isotopes not like C and O-chondrites (Clayton)! Implications: DMM is >45-90% of the mantle (to >1600 km depth). If primitive mantle 143Nd/144Nd is (instead of ) then much more than 25% of the mantle needs to be depleted to make DMM! What was once considered depleted may actually be enriched! How to preserve for 4.5 Ga? A whole new family of models are needed! Homogeneous? In the beginning. Courtesy of NASA/JPL-Caltech In detail, chondrites arent chondritic
Amelin & Rotenburg (2004) chondrules 142Nd/144Nd of chondrules with superchondritic 143Nd/144Nd? Is the Earth chondritic? Chondrules in primitive chondrites have highly variable 143Nd/144Nd. Are other protoplanetary disks homogeneous?
Gradient observed in the chemical composition of the dust inproto-planetary disks (predicted by radial-mixing models) Are other protoplanetary disks homogeneous? Nature, 2004. (0-2 AU) (2-20 AU) Part 2: Trace Element composition of a non-chondritic Earth
How to construct the spidergram: A. Backbone of the spidergram from parent-daughter ratios of radiogenic isotope systems. Start with 142Nd resultSm/Nd ratio ~6% higher than chondrites). B. Pin the spidergram to the abundance of K in the Earth, which is given by the amount of Ar in the Earth (no missing Ar) Generate continental crust and DMM U, Th and K to satisfy thermal constraints. 87Sr/86Sr from 143Nd/144Nd. Then calculate Rb/Sr.
Non-chondritic Earth Non-chondritic Earth 176Hf/177Hf from 143Nd/144Nd. Then calculate Lu/Hf.
Non-chondritic Earth Non-chondritic Earth Summary of isotope plots Backbone of the spidergram
3 segments based on parent-daughter ratios. Link the 3 segments with canonical ratios. Rare Earth Elements Splice the REEs into the backbone What about K-U-Th-Pb? K/La=constant in OIBs (330; Palme&ONeill)
K/U=constant in OIBs (11,900; Arrevalo et al.) U/Pb= (Earths 238U/204Pb=8.5 to lie on geochron) Th/U=3.9 (Earths 232Th/238U to pass through Baffin Is. lavas). Filling in the stragglers
Ba/Rb= Canonical in oceanic basalts Zr/Hf= Canonical in oceanic basalts Y/Er= Y behaves like a REE, so force it to plot b/t REEs Ti/Gd=Ti has similar compatibility as Gd, forced to be smooth Nb/U=Least constrained.Forced to be smooth b/t U and La. Spidergram has a shape, but no absolute concentrations! Standard (chondrite) model for K in the Earth: Hidden Ar reservoir
K volatile, lost during accretion, so abundance is unknown. U is refractory, so its abundance can be estimated from chondrites.~20 ppb. K/U in Earth known from basalts (~1.2x104). Calc K abundance in chondritic primitive mantle is 250 ppm. 40K decays to 40Ar (t1/2=1.3 Ga). All 40Ar in the Earth radiogenic, accumulated since accretion. There should be ~140x1018 g 40Ar Earth. Only ~95x1018 g 40Ar Earth is accounted for (atm, CC, DM). Ergo, a hidden reservoir in the Earth hosts the missing 40Ar! PM Lyubetskaya & Korenaga (2007) Use 40Ar in Earth to pin primitive mantle K concentration
Turn the problem of missing Ar into a solution: What we see is what we get: no missing Ar reservoir! Three 40Ar reservoirs: Atmosphere:66x1018g 40Ar (Turekian, 1959) Continental Crust: 1-9x1018g 40Ar (say, 4.5x1018g 40Ar) Depleted Mantle (2 independent estimates): A.Assume K in DM: x1018g 40Ar B. 40Ar flux at ridges: x1018g 40Ar Total 40Ar in Earth:95x1018g Therefore, 160 ppm K in the Earth. Atmosphere:66x1018g 40Ar. Continental Crust: 1-9x1018g 40Ar. Depleted Mantle has: Recycled reservoir Surviving portions of non-chondritic primitive mantle. (say, 24x1018g 40Ar) Spidergram with K pinned at 160 ppm
U, Th and K all about 0.6 of chondrite model Can we extract continental crust from non-chondritic primitive mantle?
Primitive Mantle = Continental Crust + Depleted Mantle New Primitive Mantle:Have to depleted >55% of the mantle to make Continental Crust! Prim Mantle (this study) Previous estimates for DM DMM (this study)=PM-CC Layered Mantle? 660km of DMM? Not if the Earth is non-chondritic!
DMM (25% mantle) DMM >55% mantle) Hofmann, 1997 Thermal budgets of a non-chondritic Earth
U, Th and K are all 66% lower than the standard model. So, 33% less radiogenic heat than the standard model.Lower Urey ratio (radiogenic/total heat) The Earth produces 46 TW. -- Standard model: ~20 TW is radiogenic heat -- New model:~13 TW is radiogenic heat. The rest is primordial heat.Is there enough uncertainty in primordial heat that we can make a non-chondritic Earth work? Who drank the Cool-Aid? -S. Shirey, 2010
Conclusions The specter of a non-chondritic bulk earth? is Primitive Mantle?! What was depleted may actually be primitive, or even enriched! Geochemical evolution of the mantlea whole new family of models:Isotopic & thermal evolution. If the Earth isnt chondritic, then we dont know some of its fundamental properties (e.g., Urey ratio, etc.) Without the chondrite model, the road ahead has no map.These are exciting times! Who drank the Cool-Aid? S. Shirey, 2010 Bill White Dave Graham Hubert Palme Hugh ONeill Bernard Bourdon Guillaume Caro Nobu Shimizu Non-chondritic BSE? FOZO What about initial 3He/4He on OJP? (and the other old flood basalts?)
.olivine phenocrysts in basalt are embedded in basaltic groundmass that has much higher [U] and [Th] than the olivine. Consequently, 4He from alpha-decay of groundmass U is implanted into the rims of the olivine grains. Who drank the Cool-Aid? -S. Shirey, 2010
Rick Carlson? Sujoy? John Lassiter? Chris Ballentine? Bill White Dave Graham Hubert Palme Hugh ONeill Bernard Bourdon Guillaume Caro Nobu Shimizu Highest 3He/4He Baffin Island lavas bracket the OJP
Jackson and Carlson (Nature, TODAY) Relationship between flood basalts and a primitive (non-chondritic) mantle
Relics of the early Earth may not be so rare? Why would this reservoir be sampled by large igneous provinces? Primitive Mantle produces more heat, melts more. Primitive Mantle is more fusible, melts more. A recipe for producing extraordinary volumes of melt? Old Reservoir, Old Idea (new possibilities)
The nominal value of CHUR0 for the continental flood basalts indicates they are derived from a reservoir which has maintained an unfractionated, chondritic Sm/Nd throughout the history of the earth. -DePaolo & Wasserburg, GRL 1976 PREMA (Prevalent Mantle) = BSE?
Jackson and Carlson (Nature, TODAY) chondrite Average MORB If the large proportion of OIB lavas with present-day 143Nd/144Nd near reflects a high proportion of non-chondritic primitive material in the mantle, then primitive material must comprise a substantial portion of the modern terrestrial mantle. Moon-forming event, and the survival of a hidden early enriched reservoir?
146Sm-142Nd systematics require that an early differentiation event happened within 30 million years of accretion. 182W-182Hf systematic require that Moon formation occurred 50 Ma or more after accretion. Thus, Moon formation (after 4.51 Ga)must have followed any early differentiation event (before 4.53 Ga). How would a hidden reservoir remain hidden during a giant impact event? Also, how to keep a hidden ENRICHED reservoir hidden? Lots of U,Th,K, so hot.plumes! Touboul et al. (2007) showed that no mare basalt sample has a 182W anomaly relative to terrestrial samples. This result suggests both that the Moon formed from the Earth after terrestrial core formation had occurred, and that the compositionally distinct source reservoirs of mare basalts formed after 182Hf had completely decayed to 182W, or later than 60 Ma after the start of solar system condensation. With the removal of the HfW evidence for rapid Moon formation, the age of the Moon remains uncertain with little convincing evidence that the Moon was a separate planetary object much prior to the age of the oldest lunar crustal rocks (4.46 Ga; Carlson and Lugmair, 1988; Norman et al., 2003; Nyquist et al., 2006). Half an Hour After the Giant Impact, based on computer modeling by A. Cameron, W. Benz, J. Melosh, and others. Copyright William K. Hartmann The alternative? A non-chondritic Earth!Is neither option palatable? Why do high 3He/4He lavas from other localities plot off of the Geochron(and have somewhat lower 3He/4He)? Recycled crust is rich in Pb, U and Th. If recycled crust mixes with ambient mantle, or surviving pieces of primitive mantle, the mixture will be shifted away from the geochron. U and Th in recycled crust will generate 4He and will reduce the 3He/4He of the mixture. Recycled crust Jackson et al. (Nature, 2010) Jackson and Carlson (Nature, TODAY) Starting composition of the EarthChondritic?
1.) Carbonaceous (C) chondrites Sun 2.) C-chondrites and Earth came from the same (homogeneous?) solar nebula, and the sun represents over 99.9% of solar systems mass. 3.)Therefore, C-chondrites Earth (non-volatile, lithophile elements like Sm and Nd) 4.)If the Earth is a C-chondrite, then Earth and chondrites have the same 143Nd/144Nd.(147Sm 143Nd + 4He) The next step requires a huge assumption: This is a log-log plot covering 10 orders of magnitude! Comparison of solar-system abundances (relative to silicon) determined by solar spectroscopy and by analysis of carbonaceous chondrites (after Ringwood, 1979) Caro et al, 2008 Nature [chondrite] has been considered to define the composition of the Solar System, Baffin Island and West Greenland picrites
Samples are from Padloping Island, east coast of Baffin Island. Lavas erupted ~62Ma as part of the proto-Iceland plume. Starkey et al., 2009 Caveat: Crustal contamination
Previous slide Jackson et al. (Nature, 2010) Larsen and Pedersen, J. Pet. 2009 Larsen and Pedersen, J. Pet. 2009 Trace elements indicate no role for continental contamination in our sample suite
Average Mantle Jackson et al. (Nature, 2010) Kent et al. (2004) obtained a trace element dataset on Baffin Island glasses (pillow rims).The glasses are extremely fresh, give pristine Pb and U. Another Caveat: Radiogenic 4He
Jackson et al. (Nature, 2010) Ref. 1 = Stuart et al., 2003; Ref. 2 = Starkey et al., 2009; Ref. 9 = Graham et al., 1998 Relationship between helium concentrations and 3He/4He. Magmatic He is hosted in the olivine, U and Th in the basalt matrix
Jackson et al. (Nature, 2010) More degassed 1.Helium is massively degassed before and during eruption. Following degassing of He, parent-daughter ratios (U/He & Th/He) are increased by many orders of magnitude. 4He generated by U and Th decay diminishes 3He/4He ratio. Lesson:Avoid measuring 3He/4He on old lavas (62 Ma)! Primitive Material in superplumes?
Torsvik et al. (Nature, 2010) PREMA? (Prevalent Mantle)
PREMA defined by the most frequently occuring 143Nd/144Nd in global OIB dataset. Zindler and Hart (1986) PREMA is isotopically similar to the highest 3He/4He lavas from Baffin Island. Is PREMA a surviving portion of a non-chondritic Primitive Mantle? PREMA chondrite Range for non-chondritic primitive mantle predicted by 142Nd/144Nd Zindler and Hart, 1986 Extracting continental crust from a non-chondritic primitive mantle
Depleted MORB mantle and continental crust are geochemically complementary. If primitive mantle 143Nd/144Nd is , instead of , then much more than 25% of the mantle needs to be depleted to make DMM! DMM is >45-90% of the mantle! DMM extends down to 1600 km? Radial variation of the RMS amplitude of relative variation of bulk sound and shear wavespeed Dashed line depicts the radial variation of the root mean square (RMS) amplitude of relative variation of bulks sound and shear wavespeed van der Hilst et al., Science 1999 Nucleosynthetic anomalies?
Ranen & Jacobsen (2006): Measured anomalies in the abundance of 137Ba and 138Ba in a variety of chondrites, and concluded that the difference in 142Nd/144Nd between chondrites and terrestrial rocks reflects nucleosynthetic heterogeneity in the solar nebula.They argued that imperfect mixing of the nucleosynthetic contributions from various stars thus could result in variations in 142Nd/144Nd that are not related to 146Sm decay. 1. These anomalies not confirmed in either previous (Hidaka et al. 2003) or more recent studies (Andreasen & Sharma 2007; Carlson et al. 2007; Wombacher & Becker 2007). 2. Although excesses in 135Ba and 137Ba, which are related to variations in the ratio of r- to s-process components, have been observed in carbonaceous chondrites, they have not been observed in ordinary chondrites or eucrites (Hidaka et al. 2003; Andreasen & Sharma 2007; Carlson et al. 2007). 3.When Ba isotopic anomalies are measured in carbonaceous chondrites, they show little or no correlation with the magnitude of 142Nd deficit measured in the same sample (Carlson et al. 2007). Ba isotopic anomalies in carbonaceous chondrites appear to have little or no significance for the interpretation of the 142Nd/144Nd difference between chondrites and terrestrial rocks. Of greater concern is the discovery that carbonaceous chondrites contain approximately 100 ppm deficits in 144Sm (Andreasen & Sharma 2006; Carlson et al. 2007), which, like 146Sm, is produced by the p-process.This result indicates nucleosynthetic variability in C-chondrites. 1.It is possible to correct for this p-process deficit in C-chondrites.A 100 ppm deficit in 144Sm/152Sm would translate into an 11 ppm deficit in 142Nd/144Nd due to the reduced abundance of 146Sm (Andreasen & Sharma, 2006). Therefore, the correction brings the average C-chondrite 142Nd/144Nd value to ~21 ppm below terrestrial, a value that is similar to that obtained for other meteorite groups. 2. P-process heterogeneity does not appear to be significant for O- and E-chondrites, basaltic eucrites or lunar samples, as all these materials have the same 144Sm/152Sm as measured for terrestrial rocks Conclusion:The observed difference between chondritic and terrestrial 142Nd/144Nd does not reflect nucleogenic heterogeneity in the solar nebula, but instead is best explained by the decay of 146Sm. -142Nd is made primarily by s-process nucleosynthesis -144Nd and 146Nd are made by a combination of s- and r-process nucleosyntheses. -146Sm is made by the p-process (Woosley & Howard 1978). Nucleosynthetic heterogeneities are a concern for interpreting Nd isotopic variations because the different isotopes of Nd and Sm are made by different nucleosynthetic processes in stars.Primitive carbonaceous chondrites display isotopic anomalies in Nd and Sm that are best explained by incomplete mixing of various nucleogenic contributions to the solar nebula, but these anomalies are found neither in ordinary or enstatite chondrites nor in basaltic eucrites. Carbonaceous chondrites thus are not good choices to represent the building blocks of the Earth. Correcting for these nucleogenic anomalies, however, still leaves all terrestrial rocks with 142Nd/144Nd higher than observed in any chondrite, most likely as a result of the decay of 146Sm in a portion of the Earth that has superchondritic Sm/Nd ratio.