Naturally occurring deposits of bitumen are formed from the remains of ancient, microscopic algae (diatoms) and other once-living things.
nˈætʃɚɹəli əkˈɜːɹɪŋ dᵻpˈɑːzɪts ʌv bɪtˈuːmɛn ɑːɹ fˈɔːɹmd fɹʌmðə ɹᵻmˈeɪnz ʌv ˈeɪntʃənt, mˌaɪkɹəskˈɑːpɪk ˈælɡiː dˈaɪəɾəmz ænd ˈʌðɚ wˈʌnslˈɪvɪŋ θˈɪŋz.