Question: when did earth's population reach 1 billion
[{'answer': '1804', 'provenance': [{'wikipedia_id': '33666830', 'title': 'World population milestones', 'start_paragraph_id': 2, 'start_character': 91, 'end_paragraph_id': 2, 'end_character': 95, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '33666830', 'title': 'World population milestones', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 976, 'bleu_score': 0.818485724863316, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15304533213616240890}, 'section': 'Section::::Abstract.'}]}]