Question: what is a solid iron layer that makes up a small amount of earth's mass
[{'answer': 'inner core', 'provenance': [{'wikipedia_id': '2939202', 'title': "Earth's inner core", 'start_paragraph_id': 0, 'start_character': 8, 'end_paragraph_id': 0, 'end_character': 18, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]