The Age of the Carbonates in Martian Meteorite ALH84001

Borg, L. E.; Connelly, James N.; Nyquist, L. E.; Shih, C.-Y.; Wiesmann, H.; Reese, Y.

doi:10.1126/science.286.5437.90

Cited by 170 publications

(123 citation statements)

References 23 publications

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“…3). Petrographic relationships show that the Ca-rich phase postdates the more abundant Mg-and Fe-rich rosettes and formed in a distinct alteration event (5,23,27). The absolute timing of this later alteration event is difficult to constrain and may represent either an event that occurred soon after the primary population of carbonate rosettes formed (∼3.9 Ga) or an even later event, perhaps the one that ejected the meteorite from Mars (∼15 Ma) (28).…”

Section: Discussionmentioning

confidence: 99%

“…The Martian meteorite ALH 84001 is a critical source for understanding the history of the Martian atmosphere, as it is the oldest known rock (crystallographic age ∼4.09 ± 0.03 Ga) (4), and its carbonate fractions (<1% wt/wt) are considered to have preserved the carbon isotope signature of the ancient atmosphere ∼3.9 Ga ago (5). These carbonates are chemically (Mg-, Ca-, and FeMn rich) and isotopically (δ 13 C VPDB = 27-64, where VPDB stands for Vienna Pee Dee Belemnite, and δ 18 O SMOW = −10-27‰, where SMOW stands for Standard Mean Ocean Water) heterogeneous on micrometer scales; carbon and oxygen isotopes show a covariant relationship that is correlated with Mg content of the mineral (6)(7)(8).…”

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confidence: 99%

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Carbonate formation events in ALH 84001 trace the evolution of the Martian atmosphere

Shaheen

Niles

Chong

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Carbonate minerals provide critical information for defining atmosphere-hydrosphere interactions. Carbonate minerals in the Martian meteorite ALH 84001 have been dated to ∼3.9 Ga, and both C and O-triple isotopes can be used to decipher the planet's climate history. Here we report Δ 17 O, δ 18 O, and δ 13 C data of ALH 84001 of at least two varieties of carbonates, using a stepped acid dissolution technique paired with ion microprobe analyses to specifically target carbonates from distinct formation events and constrain the Martian atmosphere-hydrosphere-geosphere interactions and surficial aqueous alterations. These results indicate the presence of a Ca-rich carbonate phase enriched in 18 O that formed sometime after the primary aqueous event at 3.9 Ga. The phases showed excess 17 O (0.7‰) that captured the atmosphere-regolith chemical reservoir transfer, as well as CO 2 , O 3 , and H 2 O isotopic interactions at the time of formation of each specific carbonate. The carbon isotopes preserved in the Ca-rich carbonate phase indicate that the Noachian atmosphere of Mars was substantially depleted in 13 C compared with the modern atmosphere.Martian meteorite | oxygen isotope anomaly | aqueous interaction | carbon isotope | photochemistry G eological evidence suggests that early Mars was sufficiently warm for liquid water to flow on the surface for at least brief periods, if not longer (1). Identifying the nature and duration of warmer conditions on the Martian surface is one of the key pieces of information for understanding atmosphere-hydrosphere-geosphere interactions, the evolution of the atmosphere, and potential past habitability. A better understanding of the evolution of the Martian atmosphere and, in particular, the behavior of its primary component, CO 2 , provides a means for characterizing the nature of the ancient Martian environment. The amount of CO 2 present in the atmosphere should provide critical insight into the characteristics of the Martian climate, with a denser atmosphere being more likely to be able to support prolonged warmer temperatures (2, 3).The Martian meteorite ALH 84001 is a critical source for understanding the history of the Martian atmosphere, as it is the oldest known rock (crystallographic age ∼4.09 ± 0.03 Ga) (4), and its carbonate fractions (<1% wt/wt) are considered to have preserved the carbon isotope signature of the ancient atmosphere ∼3.9 Ga ago (5). These carbonates are chemically (Mg-, Ca-, and FeMn rich) and isotopically (δ 13 C VPDB = 27-64, where VPDB stands for Vienna Pee Dee Belemnite, and δ 18 O SMOW = −10-27‰, where SMOW stands for Standard Mean Ocean Water) heterogeneous on micrometer scales; carbon and oxygen isotopes show a covariant relationship that is correlated with Mg content of the mineral (6-8). The exact process responsible for their formation is not clear, although low-temperature aqueous precipitation, biogenic production, evaporation, and high-temperature reactions are all candidate processes (9-13). Decoding the fingerprints of various oxygen-carry...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Carbonate formation events in ALH 84001 trace the evolution of the Martian atmosphere

Shaheen

Niles

Chong

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…Approximately 600 Ma later (Borg et al, 1999), secondary carbonates were deposited by low temperature hydrothermal processes in pre-existing fractures and fissures within the groundmass.…”

Section: Introductionmentioning

confidence: 99%

Origins of magnetite nanocrystals in Martian meteorite ALH84001

Thomas‐Keprta

Clemett

McKay

et al. 2009

Geochimica et Cosmochimica Acta

108

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The Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks. These carbonate disks are believed to have precipitated 3.9 Ga ago at beginning of the Noachian epoch on Mars during which both the oldest extant Martian surfaces were formed, and perhaps the earliest global oceans. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe 3 O 4 ) with unusual chemical and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that these magnetites are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of magnetite and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. For example, the magnetites might have already been present in the aqueous fluids from which the carbonates were believed to have been deposited. We have sought to resolve between these hypotheses through the detailed characterization of the compositional and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in which they are embedded. Extensive use of focused ion beam milling techniques has been utilized for sample preparation. We then compared our observations with those from experimental thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios. We conclude that the vast majority of the nanocrystal magnetites present in the carbonate disks could not have formed by any of the currently proposed thermal decomposition scenarios. Instead, we find there is considerable evidence in support of an alternative allochthonous origin for the magnetite unrelated to any shock or thermal processing of the carbonates.

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“…The large difference in both 14 C and δ 13 C measurements of organic and carbonate fractions of ALH84001 indicates that it is extremely unlikely that they could have formed from a common reservoir of carbon. Also, we know from the work of Nyquist et al (1999) that the carbonates likely formed 3.9 Gyr ago. Hence, if the organic material and carbonate coexist and were formed from a common reservoir, we would have to find a mechanism to produce the large differences in δ 13 C. If we only had the δ 13 C, we know that isotopic fractionation between methane and carbon dioxide can be large (about 70‰) at low temperatures can occur, but only under certain conditions.…”

Section: Mckaymentioning

confidence: 99%

Radiocarbon Beyond this World

et al. 2000

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ABSTRACT. In this paper, we review the production of radiocarbon and other radionuclides in extraterrestrial materials. This radioactivity can be produced by the effects of solar and galactic cosmic rays on solid material in space. In addition, direct implantation at the lunar surface of 14 C and other radionuclides can occur. The level of 14 C and other radionuclides in a meteorite can be used to determine its residence time on the Earth's surface, or "terrestrial age". 14 C provides the best tool for estimating terrestrial ages of meteorites collected in desert environments. Age control allows us to understand the time constraints on processes by which meteorites are weathered, as well as mean storage times. Third, we discuss the use of the difference in 14 C/ 12 C ratio of organic material and carbonates produced on other planetary objects and terrestrial material. These differences can be used to assess the importance of distinguishing primary material formed on the parent body from secondary alteration of meteoritic material after it lands on the earth.

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The Age of the Carbonates in Martian Meteorite ALH84001

Cited by 170 publications

References 23 publications

Carbonate formation events in ALH 84001 trace the evolution of the Martian atmosphere

Carbonate formation events in ALH 84001 trace the evolution of the Martian atmosphere

Origins of magnetite nanocrystals in Martian meteorite ALH84001

Radiocarbon Beyond this World

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