What evidence supports land at one point being covered by ocean

The answer is; the presence of diatomaceous earth in the soil.

This means that diatoms existed in the region. Diatoms are silicified microalgae that exist in oceans, brackish waters, even in freshwaters. They divide vegetatively and in large numbers. When they die, they fall off (precipiate) to the ocean beds and accumulate with sediment to form diatomaceous earth over time.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".