2. minerals 

                                 Any naturally occurring homogeneous solid that has a definite chemical composition and a distinctive internal crystal structure. Minerals are usually formed by inorganic processes.  While  this  definition  is  applicable  in most cases, there are certain notable exceptions. The term mineral is also applied to certain organic substances,such as coal,graphite,oil,and natural gas, that are obtained from the Earth for commercial use. Synthetic equivalents of various minerals, such as emeralds and diamonds, can be produced in the laboratory for experimental or commercial purposes. Although most minerals are chemical compounds, a small number (e.g., sulfur, copper, gold) are elements. The composition of a mineral can be defined by its chemical formula, and the identity of its anionic group determines the group into which the mineral is classified. For example, the mineral halite (NaCl) is composed of two elements, sodium (Na) and chlorine (Cl), in a 1:1 ratio; its anionic group is chloride (Cl-)--a halide--so halite is  classified  as  a  halide.  Minerals  can  thus be classified into the following major groups: native elements, sulfides, sulfosalts, oxides and hydroxides, halides, carbonates, nitrates, borates, sulfates, phosphates, and silicates. Silicates are the most commonly occurring minerals because silica is the most abundant  constituent  of  the  Earth's crust ( about 59 percent ). A mineral crystallizes in an orderly, three-dimensional geometric form, so that it is considered to be a crystalline material. Along with its chemical composition, the crystalline structure of a mineral helps determine such physical properties as hardness, colour, and cleavage. Minerals combine with each other to form rocks. For  example,  granite  consists of the minerals  feldspar,  quartz,  mica,  and  amphibole  in varying chemical ratios.  Rocks  are  thus distinguished from minerals by their heterogeneous composition. A mere 100  of  the  several thousand  known  types  of  minerals  constitute the main components of rocks. Minerals are treated in a number of articles.   For the composition, physical properties, occurrence, and classification of important rock-forming minerals, see Minerals and Rocks. For the characteristics, origins, and distribution of the major mineral fuels,  see Fuels,  Fossil.   For the methods of removing and refining or treating industrially important minerals, see Industries, Extraction and Processing. For minerals used primarily for personal adornment, see Dress and Adornment: Gems. For mineralogy, the scientific study of minerals, see Earth Sciences, The: Mineralogy .

 3.fossils.

                                 Remnant,  impression,  or  trace of an animal or plant of a past geologic age that has  been  preserved  in the Earth's crust. The complex of data recorded in fossils worldwide,  known as the fossil record,  is  the  primary  source of  information about the history of life on Earth. Only a small fraction of ancient organisms are preserved as fossils,  and  usuall only organisms that have a solid and resistant skeleton  are readily preserved.  Most  major groups of  invertebrate animals have a calcareous skeleton or shell (e.g., corals, mollusks, brachiopods, bryozoans). Other forms have shells  of  calcium  phosphate  ( which also occurs in the bones of vertebrates ), or silicon dioxide.  A shell  or bone that is buried quickly after deposition  may  retain these organic tissues, though they become petrified ( converted to a stony substance ) over time. Unaltered hard parts, such as the shells  of  clams  or  brachiopods,  are  relatively  common  in  sedimentary  rocks, some of great age.  The hard parts of organisms that become buried  in  sediment  may  be  subject  to  a variety of other changes during their conversion to  solid rock,  however.  Solutions may fill the interstices,  or pores,  of  the  shell  or  bone  with  calcium carbonate or other mineral salts and thus fossilize the remains,   in a process  known  as  permineralization.   In  other  cases there may be a total replacement of the original skeletal material by other mineral matter, a process known as mineralization, or replacement.  In still other cases,  circulating acid  solutions  may  dissolve  the original shell but leave a cavity corresponding to it, and circulating calcareous or siliceous solutions may then deposit a new matrix in the cavity, thus creating a new impression of the original shell. By contrast, the soft parts of animals or plants are very rarely preserved. The embedding of insects in amber and the preservation of the carcasses of Pleistocene-era mammoths in ice are rare but striking examples of the fossil preservation of soft tissues. Traces of organisms may also occur as tracks or trails or even borings.  The  great  majority  of  fossils  are  preserved  in  a  water environment  because  land  remains  are  more  easily destroyed.  Anaerobic  conditions  at the bottom  of  the  seas  or  other  bodies  of water are especially favourable for preserving fine details, since no bottom  faunas, except for anaerobic  bacteria,  are  present  to  destroy the remains. In general, for an organism to be preserved two conditions must be met:  rapid burial to retard decomposition and to prevent  the  ravaging  of  scavengers;  and  possession  of  hard  parts capable  of  being fossilized.  In  some  places,  such  as  the  Grand Canyon  in  northern Arizona,  one can observe  a  great   thickness   of  nearly  horizontal strata representing  the  deposition  of sediment  on  the seafloor  over  many  hundreds  of millions of years. It is often apparent that each layer in such a sequence contains fossils that are distinct from those of the layers that are above and below it. In such sequences of layers in different geographic locations, the same, or similar, fossil floras or faunas occur in the identical order.  The study of the fossil record has provided important information for at least four different purposes.  In recent years, geologists have been able to study the subsurface stratigraphy of oil and natural gas deposits by analyzing microfossils obtained from core samples of deep borings.