Kirschvink J L, Maine A T, Vali H
Division of Geological and Planetary Sciences, California Institute of Technology, 170-25, Pasadena, CA 91125, USA.
Science. 1997 Mar 14;275(5306):1629-33. doi: 10.1126/science.275.5306.1629.
Indirect evidence for life on Mars has been reported from the study of meteorite ALH84001. The formation temperature of the carbonates is controversial; some estimates suggest 20 degrees to 80 degrees C, whereas others exceed 650 degrees C. Paleomagnetism can be used to distinguish between these possibilities because heating can remagnetize ferrimagnetic minerals. Study of two adjacent pyroxene grains from the crushed zone of ALH84001 shows that each possesses a stable natural remanent magnetization (NRM), implying that Mars had a substantial magnetic field when the grains cooled. However, NRM directions from these particles differ, implying that the meteorite has not been heated significantly since the formation of the internal crushed zone about 4 billion years ago. The carbonate globules postdate this brecciation, and thus formed at low temperatures.
对陨石ALH84001的研究报告了火星存在生命的间接证据。碳酸盐的形成温度存在争议；一些估计表明是20摄氏度至80摄氏度，而另一些则超过650摄氏度。古地磁学可用于区分这些可能性，因为加热会使亚铁磁性矿物重新磁化。对来自ALH84001破碎带的两个相邻辉石颗粒的研究表明，每个颗粒都具有稳定的天然剩磁（NRM），这意味着火星在这些颗粒冷却时具有强大的磁场。然而，这些颗粒的NRM方向不同，这意味着自约40亿年前内部破碎带形成以来，这块陨石未受到显著加热。碳酸盐小球形成于这次角砾化之后，因此是在低温下形成的。
