1 SEARCHING FOR SPECTRAL SIGNATURES OF FOSSILS: MODELLING AND APPLICATIONS Politi R., Marzo G.A., Blanco A., Fonti S., Orofino V. Physics Department, University of Lecce Address: C.P. 193, 73100 Lecce, Italy, Tel.: +390832297479 Fax: +390832297505 e-mail: Romolo.Politi@le.infn.it Abstract. Using a numerical model together with a suitable set of experimental measurements, we show that some effects caused by microfossil inclusions in a crystalline matrix should be detectable in the IR spectra and, most of all, by Raman spectroscopy. Such effects are basically due to the increase of disorder linked to the presence of microfossils. Our findings can be very useful for astrobiological investigations connected with future Mars missions 1. Introduction. The likely past existence of liquid water on the surface of Mars could suggest the presence of simple forms of life on the planet (bacteria, archeae or eukariota) [1,2]. In particular we focalize our attention on the possible evolution of basic forms of life in the Noachian age when an ocean was believed to exist. In this scenario it can be useful to foresee and organize a set of laboratory measurements which can best provide a means for fossils and microfossils detection. For the interpretation of the experimental data we have developed a simple model of fossils inclusions in a Calcite monocrystal. The choice of Calcite (CaCO 3 ) is due to the consideration that, looking for microscopic forms of life, it is reasonable to search in sedimentary rocks and calcite is the most common sedimentation product found in paleo-basins of standing water. In this work we applied our method to some samples collected at the K-T Boundary layers in Gubbio, Italy. In this geological sequence, on either side of the Iridium layer, it is possible to find samples with the same chemical composition (CaCO 3 ), but with different fossils content. As laboratory analyses we have chosen three different techniques which can give complementary information about the properties of the samples. The techniques are Visual Albedo for morphology studies, FT-IR Spectroscopy for a global view of the crystalline status and Raman Spectroscopy for information of the local structure of our samples. 2. The Model. In order to build our model we assembled the elementary cell of Calcite (Trigonal - Hexagonal Scalenohedral) both mathematically and graphically by means of several “ad hoc” routines written using IDL language. Once the synthetic cell has been obtained, we simply joined such “bricks” to simulate a perfect crystal plane representing an ideal picture of our Calcite sample. In this ideal view of the crystal we inserted some circular. At this stage of work we decided to adopt a simple approach, since we found that the shape of the inclusions has no major influence on the comparison between modellization and measurements. This because the FT-IR beam is much larger than the size of the single inclusion, while the Raman beam is smaller. Figure 1. The rendered model of the crystal plane with the fossil inclusions simulated by cells with random orientations. 3. Analysis Technique. Visual Albedo can give information about the morphology, important to discriminate between microfossils and inclusions of different nature. We overlapped three different albedo images in the R (0.63 -0.69 µm), G (0.54 - 0.60 µm) and B band (0.52 - 0.54 µm) obtaining something similar to a standard photo, but with more information. We have done a survey of our sample and from the resulting map we have been able to identify some features suggesting the presence of microfossils. On each candidate found in the sample, we performed the FT-IR and Raman spectroscopy. Figure 2. Two examples of likely fossil inclusions: 160403k on the left and 160403p on the right. In this paper we report only two examples of the candidates found in our sample, 160403k and 160403p, shown in Figure 2. Figure 3 reports the comparison between the experimental spectrum (solid line) and theoretical spectrum (broken line). The latter was