"age.universe" <-
structure(list(lower = c(7.5e-05, 0.24, 1, 0.02, 2, 10, 16, 12.07, 
10, 12, 11, 9.5, 13, 11.2, 13.56), upper = c(NA, NA, 10, NA, 
NA, 15, 20, NA, NA, NA, 20.2, 15.5, 14, 20, 13.84), year = c(1760, 
1831, 1852, 1897, 1929, 1970, 1980, 1996, 1997, 1999, 1999, 2001, 
2002, 2003, 2003), source = structure(c(2, 11, 1, 12, 6, 14, 
14, 4, 9, 8, 5, 3, 7, 10, 13), class = "factor", .Label = c("Bok. galactic clusters", 
"Buffon. time of cooling from molten state. Earth", "Cayrel", 
"Chaboyer", "Cowan ", "E. Hubble. Redshift", "Hubble telescope", 
"Hubble telescope. Hubble constant", "Krauss", "Krauss, Chaboyer, Science, 2003", 
"Lyell. age of mollusks. Earth", "Thomson. Thermodynamics of earth. Min is between 20-400million", 
"WMAP satellite. Microwave radiation", "various"))), .Names = c("lower", 
"upper", "year", "source"), row.names = c("13", "14", "11", "15", 
"1", "5", "8", "4", "2", "6", "10", "9", "7", "3", "12"), class = "data.frame")