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TOPIC: Planetary mantle differentiation

Blobrana

L

Posts: 131433

Date: May 1 21:00 2012

Samarium-146	Permalink

A 'faster-ticking clock' indicates the early solar system may have evolved faster than we think, say researchers Our solar system is four and a half billion years old, but its formation may have occurred over a shorter period of time than we previously thought, says an international team of researchers from the Hebrew University of Jerusalem and universities and laboratories in the US and Japan. Establishing chronologies of past events or determining ages of objects require having clocks that tick at different paces, according to how far back one looks. Nuclear clocks, used for dating, are based on the rate of decay of an atomic nucleus expressed by a half-life, the time it takes for half of a number of nuclei to decay, a property of each nuclear species. Read more __________________

Blobrana

L

Posts: 131433

Date: Sep 23 07:14 2011

Planetary mantle differentiation	Permalink

Title: Shorter 146Sm half-life and revised 146Sm-142Nd ages of planetary mantle differentiation Authors: N. Kinoshïta, M. Paul, Y. Kashiv, P. Collon, C.M. Deibel, B. DiGiovine, J.P. Greene, D.J. Henderson, C.L. Jiang, S.T. Marley, T. Nakanishi, R.C. Pardo, K.E. Rehm, D. Robertson, R. Scott, C. Schmitt, X.D. Tang, R. Vondrasek, A. Yokoyama The extinct short-lived nuclide 146Sm, synthesized in stellar events by the p-process, serves as both an astrophysical and geochemical chronometer through measurements of isotopic anomalies of its alpha-decay daughter 142Nd. Evidence of live 146Sm, quantitatively established for the early Solar System, constrains the time between p-process nucleosynthesis and condensation of the first solid materials. Samarium-146 is used also to date silicate mantle differentiation events in a number of planetary bodies, including Earth. We performed a new measurement of the 146Sm half-life and our result, t = 68±7 (1sigma) million year (Ma), is significantly shorter than the value currently used for 146Sm-142Nd chronology (103±5 Ma). We show here that the shorter 146Sm half-life value implies a higher initial Solar System ratio, (146Sm/144Sm)_0 = 0.0094±0.0005 (2sigma), than the recently derived value 0.0085±0.0007, or that used in most studies 0.008±0.001. Planetary differentiation processes dated by 146Sm-142Nd converge to a shorter time span, due to the combined effect of the new 146Sm half-life and (146Sm/144Sm)_0 values. The revised 142Nd age of the recently dated Lunar ferroan anorthosite (FAN) 60025, is in agreement with its 147Sm-143Nd age; their weighted average, 196±11 (2sigma) Ma after Solar System birth, is consistent with the 208.8±2.4 Ma Pb-Pb age and with the age derived here (170±15 Ma) from an isochron of Lunar rocks. Read more (1047kb, PDF) __________________

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