Question: when did the trans saharan trade routes begin
[{'answer': 'at least 7000 BC', 'provenance': [{'wikipedia_id': '1437959', 'title': 'Trans-Saharan trade', 'start_paragraph_id': 2, 'start_character': 77, 'end_paragraph_id': 2, 'end_character': 93, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '1437959', 'title': 'Trans-Saharan trade', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 428, 'bleu_score': 0.9328730072843131, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12460021393633812784}, 'section': 'Section::::Abstract.'}]}]