The first 'Earth Summit', officially known as the United Nations Conference on Environment and Development (UNCED), was organized in Rio de Janeiro, Brazil, in 1992. This landmark conference addressed pressing environmental and development issues at a global scale and laid the groundwork for sustainable development initiatives worldwide.

Explanation:

• The conference is significant for introducing important international agreements, such as the Rio Declaration on Environment and Development, and the Agenda 21, which is a comprehensive plan of action to be taken globally, nationally, and locally by organizations of the United Nations System, governments, and major groups.
• The 'Earth Summit' also paved the way for future environmental action and agreements by establishing important conventions like the Convention on Biological Diversity and the Framework Convention on Climate Change (UNFCCC), which later led to the Kyoto Protocol and Paris Agreement.

Elimination of Options:

• 1991: There was no major global environmental conference held in this year.
• 1992: The correct answer, marking the year of the first 'Earth Summit'.
• 1993: No significant environmental summit was held this year concerning the scope of the question.
• 1994: Similar to 1991 and 1993, there was no specific 'Earth Summit' or major antecedent to the summit in this year.

Thus, the correct answer is 1992.