when were fossil fuels first used
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when were fossil fuels first used
when were fossil fuels first used as energy
when did humans first use fossil fuels
when were fossil fuels created
when was fossil fuels invented
how long have fossil fuels been used
when were fossil fuels discovered
when did fossil fuels form
how long ago were fossil fuels created
origins of fossil fuels
when were fossil fuels first used, when were fossil fuels first used as energy, when did humans first use fossil fuels, when were fossil fuels created, when was fossil fuels invented, how long have fossil fuels been used, when were fossil fuels discovered, when did fossil fuels form, how long ago were fossil fuels created, origins of fossil fuels