These natural deposits of bitumen have been formed during the Carboniferous period, when giant swamp forests dominated many parts of the Earth.
ðiːz nˈætʃɚɹəl dᵻpˈɑːzɪts ʌv bɪtˈuːmɛn hɐvbɪn fˈɔːɹmd dˈʊɹɹɪŋ ðə kˌɑːɹbənˈɪfɚɹəs pˈiəɹɪəd, wˌɛn dʒˈaɪənt swˈɑːmp fˈɔːɹɪsts dˈɑːmᵻnˌeɪɾᵻd mˈɛni pˈɑːɹts ʌvðɪ ˈɜːθ.