Why do scientists believe that ancient green algae could be the ancestors of higher plants?

Initially, there was only water on the ground, therefore, most likely algae appeared first. After the appearance of land, plants began to develop (roots appeared, etc.).

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.