Carbon and hydrogen.
The simplest group of organic molecules are the alkanes which have only these 2 elements. Eg methane, CH4.
The main type of evidence the scientists used is fossils.
Palaeontologists study plants and animals that existed in the geologic past. To do so, they use fossils and try to determine an organism's evolution and relationship with the environment and other organisms. In this example, palaeontologists used fossils from ancient horses that have gone extinct and try to decipher their evolutionary path. Recognising the evolutionary steps of the ancient horses will make it possible to compare them to the modern horses.
