Question: when does thanos first appear in marvel movie
[{'answer': '2012', 'provenance': [{'wikipedia_id': '701741', 'title': 'Thanos', 'start_paragraph_id': 2, 'start_character': 104, 'end_paragraph_id': 2, 'end_character': 108, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]