220 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1954 



Let US try to answer the question of their formation first — that is, 

 how and where. Studies of the many meteorites that have landed 

 upon the earth, many of which may be observed in various museums 

 throughout the world, support the hypothesis that they were once a 

 part of a planet. In the development of this parent planet as the 

 cosmic dust collected into a body, heat would gradually develop as 

 the planet's mass increased (Weizsacker, 1943, 1949). Heating would 

 result not only from the dissipation of potential energy in the con- 

 traction process and from radioactivity, supplemented by radiant en- 

 ergy from the sun, but especially from chemical reactions within the 

 planet's body. As a result the planet would become a molten mass 

 with an estimated temperature near 3,000° C. (Klotz, 1949; Brown, 

 1949) and in which boiling and/or settling processes would result in 

 the concentration of the heavier materials in the planet's core with 

 lighter and lighter material tending to attain chemical and physical 

 equilibrium at higher levels as the various chemical reactions were 

 concluded. Thus the lightest substances, the glasses and glassy sili- 

 cates, would become concentrated in layers or pools on or near the 

 surface of the planet. If the planet had been small, that is of the order 

 in size of our moon or the planet Mars, the materials composing it 

 would have solidified without appreciable chemical separation (Urey, 

 1951a, b), as has been the case with those members of the solar sys- 

 tem. Hence, to account for the resulting temperatures and separa- 

 tions of the different metal and stony phases (illustrated by the dif- 

 ferent types of meteorites) a planet approximating the earth in size 

 and general physical and chemical characteristics is required (Brown 

 and Patterson, 1948). 



From the above picture we have a planet with a nickel-iron core 

 surrounded with troilite (principally ferrous sulfide) and olivine (a 

 magnesium and iron silicate) and topped with the glassy silicates and 

 glasses. The glasses should be uppermost, that is on or near the sur- 

 face. As the planet cooled, the surface would solidify first. After the 

 outer crust had been formed volcanic processes similar to those within 

 the earth would be expected to be operative. Indeed meteorites in 

 various museums clearly show that the process by which they were 

 formed was very complex. There was extensive mixing, crushing, 

 melting, segregation and remelting. In fact no theory has yet been 

 proposed that will account for many of the different structures dis- 

 played by polished surfaces of meteorites. 



No sedimentary rocks, such as shales, limestones, etc., nor structures 

 proving the presence of any type of plant or animal life have ever 

 been observed in any meteorite. That is, no water erosion or organic 

 chemical reactions have left traces within any meteoric material. Al- 

 though traces of organic acids have been reported in certain carbo- 



