Life on planet Earth exists in a variety of shapes: bacteria, plants, insects, animals… Complex organisms like us humans have evolved over billions of years from a primordial and very simple form of life. But how was that first living organism born on Earth?
Some scientists believe that comets brought life to our planet. According to this theory, called panspermy, the ingredients of life already exist in the Universe and are transported on various planets by asteroids and comets.
Comets are leftovers of the primitive space matter that formed when our Solar System was born. They have been travelling in Space for 4.6 billion of years, practically intact, and they are made mainly of ice and dust. What makes comets so interesting is the fact that they contain two key ingredients for life: water and organic molecules.
Organic molecules are formed by atoms of hydrogen, oxygen, carbon and nitrogen, and are the building blocks of all the living creatures we know. Amino acids, which bind together in chains to form proteins, are among these organic molecules.
Various space missions have revealed the presence of amino acids on comets. Even the recent Rosetta mission, carried out by the European Space Agency, has found the amino acid called “glycine” on comet 67P; it has also found phosphorus on the comet: an important element in cell components, like DNA and the cell membrane.
Some scientists think that the energy released when a comet impacts a planet allows the alignment of amino acids in short protein chains, thus creating the first building blocks for the development of a living creature. After that, minerals in clay – which is found on many planets – facilitate the evolution of life by allowing the molecules to rearrange and recombine in more complex structures.
Around four billion years ago, when Earth was just born, our planet was hit by a large number of asteroids and comets. According to some scientists, the comets that fell on Earth during that period may have delivered the first organic molecules, and life could have originated from them.
This means that we could all be children of a comet!