How the Year came about:
In April 2005, the initiative for a Year was put forward by the Tanzanian Delegation to UNESCO's Executive Board, which adopted the proposal nem. con. A Draft Resolution on proclamation of the International Year of Planet Earth in 2008 was adopted by Commission III at UNESCO's 33rd General Conference on 12 October 2005. By then, 97 UN Member States had explicitly expressed support for the initiative.

See also:
:: Global Launch Event (12 - 13 February 2008)
:: Photo contest on "The Changing Face of the Earth"
:: Planet Earth: Earth Sciences for Society
:: UNESCO Earth Sciences website

On the occasion of the launching of the International Year of Planet Earth 2008, UNESCO presents this exhibition from 14 to 17 February.
It celebrates the beauty, diversity and complexity of the Earth and explores the challenges facing our planet, highlighting the role of UNESCO and its sustainable development.
The themes of the exhibition are: Earth System; Dynamic Earth, Diverse Earth; Changing Earth; and Sustaining the Earth illustrated through multimedia elements such as the Magic Planet, a digital video globe® courtesy of NASA, and the PentaGlobe® created by Laurent Metterie.
Related link:
:: Exhibition: "Planet Earth: from Space to Place"