The main criteria for living cells are a membrane capable of separating the inside of the cell from its surroundings, genetic material capable of being reproduced, and the ability to acquire and use energy (metabolism). But how did those early single cells “come together” to form organic compounds and eventually self-replicate?

The mechanism(s) that eventually helped to form organic compounds is still a highly debated subject. One suggestion is that the first cells collected together and eventually self-replicated in ocean foam. Another theory states that the clay may have contributed its own energy (clay can store, transform, and release chemical energy) to encourage the growth of cells. British-born American theoretical physicist Freeman Dyson (1923–) hypothesized the “double origin theory,” in which “two separate kinds of creatures [exist], one kind capable of metabolism without exact replication and the other kind capable of replication without metabolism.” And still another idea is that larger molecules called polymers (proteins bonded together) somehow connected together and eventually became self-replicating.