Ältestes erhaltenes Material der frühen Erde

[styria-met]

http://stores.ebay.com/Crystal-World-Prehistoric-Journeys/Rough-Mineral-Rock-/_i.html?_fsub=540123012&_sid=47993852&_trksid=p4634.c0.m322

Hier gibts nun auch die Zirkone!!!

Aber Achtung: Es dürfte fragwürdig sein, wie viele Zirkone überhaupt in den Steinen stecken und ob überhaupt einer davon überhaupt ein übermäßig hohes Alter aufweist. Selbst nachweisen wird man beides wohl nie können.

Habe mir von ihm eine Scheibe schicken lassen 

Stefan

[karmaka]

Ergänzendes zum Thema:

Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography
by John W. Valley et al

Nature Geoscience (2014), doi:10.1038/ngeo2075

LINK

LINK

The only physical evidence from the earliest phases of Earth’s evolution comes from zircons, ancient mineral grains that can be dated using the U–Th–Pb geochronometer1. Oxygen isotope ratios from such zircons have been used to infer when the hydrosphere and conditions habitable to life were established2, 3. Chemical homogenization of Earth’s crust and the existence of a magma ocean have not been dated directly, but must have occurred earlier4. However, the accuracy of the U–Pb zircon ages can plausibly be biased by poorly understood processes of intracrystalline Pb mobility5, 6, 7. Here we use atom-probe tomography8 to identify and map individual atoms in the oldest concordant grain from Earth, a 4.4-Gyr-old Hadean zircon with a high-temperature overgrowth that formed about 1 Gyr after the mineral’s core. Isolated nanoclusters, measuring about 10 nm and spaced 10–50 nm apart, are enriched in incompatible elements including radiogenic Pb with unusually high 207Pb/206Pb ratios. We demonstrate that the length scales of these clusters make U–Pb age biasing impossible, and that they formed during the later reheating event. Our tomography data thereby confirm that any mixing event of the silicate Earth must have occurred before 4.4 Gyr ago, consistent with magma ocean formation by an early moon-forming impact4 about 4.5 Gyr ago.

[karmaka]

Aktuelles zum Thema:

Pervasive remagnetization of detrital zircon host rocks in the Jack Hills, Western Australia and implications for records of the early geodynamo

Benjamin P. Weiss, Adam C. Maloof, Nicholas Tailby, Jahandar Ramezani, Roger R. Fu, Veronica Hanus, Dustin Trail, E. Bruce Watson, T. Mark Harrison, Samuel A. Bowring, Joseph L. Kirschvink, Nicholas L. Swanson-Hysell, Robert S. Coe

Earth and Planetary Science Letters
Volume 430, 15 November 2015, Pages 115–128

LINK

[karmaka]

Neues zu einer spannenden Frage:

Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon

Elizabeth A. Bell, Patrick Boehnke, T. Mark Harrison, and Wendy L. Mao

PNAS2015 ; published ahead of print October 19, 2015, doi:10.1073/pnas.1517557112

PDF (Volltext)
abstract
supporting information

Significance

Evidence for carbon cycling or biologic activity can be derived from carbon isotopes, because a high 12C/13C ratio is characteristic of biogenic carbon due to the large isotopic fractionation associated with enzymatic carbon fixation. The earliest materials measured for carbon isotopes at 3.8 Ga are isotopically light, and thus potentially biogenic. Because Earth’s known rock record extends only to ∼4 Ga, earlier periods of history are accessible only through mineral grains deposited in later sediments. We report 12C/13C of graphite preserved in 4.1-Ga zircon. Its complete encasement in crack-free, undisturbed zircon demonstrates that it is not contamination from more recent geologic processes. Its 12C-rich isotopic signature may be evidence for the origin of life on Earth by 4.1 Ga.

Abstract

Evidence of life on Earth is manifestly preserved in the rock record. However, the microfossil record only extends to ∼3.5 billion years (Ga), the chemofossil record arguably to ∼3.8 Ga, and the rock record to 4.0 Ga. Detrital zircons from Jack Hills, Western Australia range in age up to nearly 4.4 Ga. From a population of over 10,000 Jack Hills zircons, we identified one >3.8-Ga zircon that contains primary graphite inclusions. Here, we report carbon isotopic measurements on these inclusions in a concordant, 4.10 ± 0.01-Ga zircon. We interpret these inclusions as primary due to their enclosure in a crack-free host as shown by transmission X-ray microscopy and their crystal habit. Their δ13CPDB of −24 ± 5‰ is consistent with a biogenic origin and may be evidence that a terrestrial biosphere had emerged by 4.1 Ga, or ∼300 My earlier than has been previously proposed.