Question: what mineral in 4 ga sandstones was dated to determine the age of the earth
[{'answer': 'zircon', 'provenance': [{'wikipedia_id': '4087668', 'title': 'Oldest dated rocks', 'start_paragraph_id': 2, 'start_character': 821, 'end_paragraph_id': 2, 'end_character': 827, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '4087668', 'title': 'Oldest dated rocks', 'start_paragraph_id': 6, 'start_character': 0, 'end_paragraph_id': 6, 'end_character': 717, 'bleu_score': 0.9051729342359011, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 797987785410744269}, 'section': 'Section::::Oldest rocks by category.:Oldest terrestrial material.\n'}]}]