Question: when did prokaryotic cells first appear on earth
[{'answer': 'approximately 3.5 billion years ago', 'provenance': [{'wikipedia_id': '19172225', 'title': 'Prokaryote', 'start_paragraph_id': 35, 'start_character': 55, 'end_paragraph_id': 35, 'end_character': 90, 'bleu_score': 1.0, 'section': 'Section::::Evolution.\n'}]}, {'provenance': [{'wikipedia_id': '19172225', 'title': 'Prokaryote', 'start_paragraph_id': 35, 'start_character': 0, 'end_paragraph_id': 35, 'end_character': 444, 'bleu_score': 0.9712154609069981, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16442118215580704671}, 'section': 'Section::::Evolution.\n'}]}]