Venus has an incredibly thick atmosphere which has a high component of carbon dioxide gas. Carbon dioxide is a major greenhouse gas, with tremendous capability to trap solar radiation and raise global temperatures. Mercury, on the other hand, due to its close proximity to the sun, has little to no atmosphere. So while Mercury is closer to the sun, it is Venus which has the higher daily temperature, due largely to the "blanket" of carbon dioxide in its atmosphere. Mercurys appearance bears a striking resemblance to that of our moon, which also has little to no atmospheric composition. Mercury is covered in craters, the results of multiple meteoric collisions, which would normally burn up upon entry into the atmosphere. Temperatures on Venus can soar upwards of 453 degrees on the Celsius scale, which is over four times the boiling point of water.
venus has an incredibly thick atmospere.The atmospheric pressure on the surface of Venus is 93 times greater than what we experience on Earth.You'd have to swim down to 1 km beneath the surface of the ocean to experience that pressure.Furthermore,the atmosphere of Venus is made up almost entirely of carbon dioxide,which we know is a greenhouse gas,that helps trap heat better.
Mercury is closest to the sun, this is true. However, because of its proximity to the sun it lacks an atmosphere. Mercury's gaseous molecules reached escape velocity long ago and the atmosphere was 'burned off' leaving a vacant wasteland of rock with a similar surface to the earth's moon. There is nothing to hold in solar radiation, thus is flies out into space.
Venus is a different story. Its atmosphere is primarily composed of carbon dioxide - the primary green house gas -, which acts like a one-way door. The solar heat enters, but it cannot leave. Thus, an oven is created. This is why Venus has no water. Pictures suggest that Venus once had an aqueous environment, but because of climatic changes and intense heat.... it evaporated. Also, because of an overactive core, Venus seems to recreate its continents every 10 years. So, we do not expect to find fossils or many bacteria.