Which of the following is/are true about the greenhouse effect?
a. greenhouse gases redirect infrared radiation back to the earth
b. the greenhouse effect is defined primarily as the phenomenon that prevents ultraviolet light from reaching the earth
c. it is something that did not exist before humans started using fossil fuels
d. none of these

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Many archeologists and anthropologists disagree with dr. thorne's view.  thorne strongly believes that what many calls "homo erectus"  was in fact  homo sapiens,  and that they migrated out of africa almost 2 million years ago and dispersed throughout europe and asia. that's way different  from what scientists have always believed about the evolution of the species.