In the early 1960s he showed that a greenhouse effect should be operating on Venus and calculated its surface temperature to be 500–800 K. He repeated H. C. Urey and S. L. Miller’s experiment of irradiating a gas mixture resembling the Earth’s primordial atmosphere, and found among the products many organic chemicals that are essential to life. He was best known for his espousal of the possibility of extraterrestrial life, and for his popular science writing.