Question: when was the first earth summit un conference
[{'answer': 'June 1992'}, {'provenance': [{'wikipedia_id': '324783', 'title': 'Earth Summit', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 281, 'bleu_score': 0.9418562503469401, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3815421926437451176}, 'section': 'Section::::Abstract.'}]}]