If there were no oceans, and the Mariana Trench, which is the deepest part of the world's oceans, was completely exposed, the sun would indeed illuminate its bottom. The Mariana Trench would essentially become a large, deep valley on land, and sunlight would penetrate the atmosphere and reach the bottom of the trench.
However, it's important to note that the Mariana Trench is approximately 10,911 meters (35,797 feet) deep, and sunlight's ability to reach the bottom would depend on various factors. Light penetrates water and gets absorbed or scattered, causing it to diminish with depth. In clear ocean water, sunlight can penetrate several hundred meters, but beyond that, it becomes increasingly dark.
On land, the atmosphere also affects the amount of sunlight reaching the surface. The atmosphere scatters and absorbs sunlight, reducing its intensity as it travels through the air. Therefore, even if the Mariana Trench were exposed on land, the sunlight reaching the bottom would be considerably diminished compared to the surface.
Additionally, without the presence of water, the Mariana Trench would lack the unique ecosystem and conditions that support various forms of life found in the deep ocean.