2020 Volume 129 Issue 6 Pages 871-880
All living organisms found so far consist of cells with a micro-water droplet surrounded by a lipid bilayer. Such a compartment structure is necessary for living organisms to repress the amplification of parasitic entities. This role of cellular structures is especially important for the primitive lifeforms that first appeared on ancient Earth. This complex lipid-based cell boundary is considered to have been acquired later in the long evolutionary history of life. Instead, ancient life-forms utilized cell-like structures that could be supplied from the ancient Earth environment. What kinds of structure could be utilized by ancient life-forms? Reviewed here are previous hypotheses regarding ancient cell-like structures, such as compartment structures formed inside a hydrothermal vent or on a rock surface, water droplets in the air that spread from geysers, and vesicles composed of simple amphiphilic molecules. Also introduced are a recent experimental verification of droplets in the air repressing parasite amplification using Spiegelman's RNA replication system. Our understanding of the origins of cellular structures is still limited because of a lack of appropriate experimental examinations based on a deeper understanding of the ancient Earth environment, which can be achieved only by collaborations between geologists and biochemists.