Final answer:
In the 1970s, the Soviet Venera landers confirmed that Venus is uninhabitable, with Venera 7 being the first to land on Venus and broadcast data in 1970.
Step-by-step explanation:
Human spacecraft first concluded that Venus was uninhabitable during the successful missions of the Soviet Venera landers in the 1970s. The first to land and transmit data from Venus' surface was Venera 7 in 1970, which communicated for 23 minutes before succumbing to the harsh conditions. Venus was found to be extraordinarily inhospitable—with a thick atmosphere causing a significant greenhouse effect, extremely high surface temperatures, and surface pressure that is almost 92 times that of Earth. Further missions, including additional Venera probes, confirmed these findings through photographs of the surface, atmospheric analysis, and soil composition studies that revealed a desolate landscape with igneous rocks, primarily basalts, and evidence of lava flows. Additional Venera probes and landers followed, capturing images of the surface and analyzing the atmosphere and soil. These missions provided conclusive evidence that Venus is inhospitable for humans.