Although the progression of evolution is well understood after life first appeared on Earth, the origin of that initial life is still largely speculative. Applied physicists from Harvard, Princeton and Brandeis have suggested a possible candidate for the earliest cells: clay bubbles.
Montmorillonite, first found in the similarly named region of France, is a naturally occurring clay that appears in tiny (one micron across) plates. This type of clay has been previously shown to be a chemical catalyst, assisting in the formation of both RNA and lipids.
According to the researchers, when suspended in water, montmorillonite clay will spontaneously form tiny capsules around any air bubbles it encounters. Because the clay is microscopically porous, that air bubble inside the clay sphere is soon replaced with water. The pores are just large enough to allow single nucleotides and other organic building blocks to enter. Once inside the shell, the montmorillonite catalyzes the formation of larger molecules that are now trapped inside. And voila! You have your first proto-cell.
According to first author Anand Bala Subramaniam,
Whether clay vesicles could have played a significant role in the origins of life is of course unknown, but the fact that they are so robust, along with the well-known catalytic properties of clay, suggests that they may have had some part to play.
Caption: Fatty-acid liposomes compartmentalize inside a clay vesicle.
Credit: Anand Bala Subramaniam, Harvard School of Engineering and Applied Sciences.