Discovery Science: Earth- Evolution – The First Biological Molecules

Earth Science:  Origins Of Life

The origins of life on Earth may never be proved with complete certainty. It seems likely that simple organic molecules combined under the right environmental conditions, eventually producing cell-like organisms.

From these, prokaryotic and later eukaryotic cells developed. These cells were the starting point for the evolution of multicelled organisms such as today’s plants, animals, and human beings.

Earth Science: Biology – Evolution – The First Biological Molecules

The primordial soup theory and the biofilm theory are the most popular explanations of how molecules became organized life forms. The panspermia theory, which says that life arrived on comets, is less discussed.

Scientists in many fields have offered theories in their attempts to solve the mystery of the appearance of life on Earth. Since Louis Pasteur first observed bacterial cells dividing under a microscope, biology has recognized the basic concept that life arises only from already existing life. An exception to this rule would seem to be found in the first appearance of life on Earth. Physical and chemical conditions then were very different from today.

The first organic molecules, from which life first developed, were seemingly produced when energy was added to nonliving material about 3.4 billion to 4 billion years ago. The primordial soup theory described the mechanisms and individual steps in this process, which was recreated in laboratory experiments in 1953. According to this hypothesis, simple organic molecules formed from chemical reactions among inorganic molecules in the primordial sea.

After the primordial soup theory, the most popular theory of life’s origins is the biofilm theory. According to this theory, the first components of life, and life itself, originated around heat sources in the sea. The panspermia or exogenesis theory suggests that life first arrived on Earth via a meteorite collision. The mechanisms proposed for interstellar panspermia are hypothetical and unproven, and the theory is given little credence among scientists.

Hydrothermal vents: breeding grounds of life

The hydrothermal vents found on the ocean floor are particularly interesting to the study of the origins of life. Black smokers are those vents which emit very hot water, darkened by its high sulfide content. The mineral pyrite forms when the hot water contacts cold seawater.

The surface of pyrite crystals has the special ability to form molecules that accumulate as thin skins, or biofilms. This characteristic of pyrite is now the focus of research. According to one scientific opinion, it was only a matter of time before the components connected to form organic molecules and, ultimately, a primitive form of life.


In 1953, American biologist and chemist Stanley Lloyd Miller astonished the experts. In a system of glass tubes, he imitated the first atmosphere, ocean, and thunderstorm. He boiled water, then added ammonium, methane, and hydrogen to the steam. The gas was exposed to an electric current.

Within a few days, organic compounds like amino acids formed in the water. The mystery of the origins of life seemed to be solved. The term “primordial soup” was coined to describe this process.