Ahrens, L.H.
Distribution of the element in our planet
McGraw-Hill, 1965
Buku Teks
Ballard, Robert D.
Exploring our living planet
National Geographic Society, 1983
Buku Referensi
Our planet, our health : report of the WHO Commission on Health and Environment. / WHO Commission on Health and Environment.
World Health Organization, 1992
Buku Teks
Moon, Glenn W.
Story of our land and people
Holt, Rinehart and Winston, 1964
Buku Teks
Edel, May
The story of our ancestors
Little, Brown, 1955
Buku Teks