古代 gǔdài HSK3 antiquity Definitions Defs Origin Strokes Stroke Words Sentences Sents 古代史 gǔdàishǐ ancient history 元古代 Yuángǔdài Proterozoic Proterozoic (geological era 2500-540m years ago)太古代 Tàigǔdài Archaeozoic Archaeozoic (geological era before 2500 million years ago)