Issues in Biology - Where Does Life Come From?

Issues in Biology

Where does Life come from?

The origin of life or prebiotic evolution means the spontaneous generation of life in a 'primordial soup' containing small organic molecules in salt water. Such a process is generally believed not to be possible (or successful) in today's ecosystems, unless undertaken in controlled laboratory settings. The latter awaits experimental proof. In order to understand the spontaneous formation of life an appropriate definition of life must be at hand. Derived from an analysis of today's organisms life is usually defined at the cellular level. In this definition, the smallest or simplest forms of life are single cell organisms which include bacteria, archaea (halophiles and thermophiles; live in extreme environments), and protozoans (eukaryotic single celled microorganisms, e.g. baker's yeast, paramecium, or amoebae). All modern life forms share fundamental molecular mechanisms, most notably protein biosynthesis and the use of DNA and RNA for reproduction and energy metabolism. Based on these observations, theories on the origin of life attempt to find a mechanism explaining the formation of a primordial single cell organism from which all modern life originates. The primordial cell is thought to form itself through beneficial packaging of self-replicating units in lipid particles (liposomes or vesicles resembling modern cell membranes). The most pressing question is how closely modern organisms resemble a primordial cell. Evidence of prebiotic evolution is obtained through simulating and replicating such an event that happened about 3.5 billion years ago. Although biochemical evidence first obtained in the 1950s showed the spontaneous generation of amino acids in a replica of the 'primordial soup', most biologist now believe that amino acids which are the building blocks of proteins and peptides, today's essential tools in all life forms, were not important at this earliest stage and that proteins and enzymes were indeed preceded by RNA type molecules which still plays an essential role in modern metabolism including energy metabolism, enzymatic catalysis (e.g. protein biosynthesis), and processing and storage of genetic information. DNA, this modern molecular marvel and blueprint of life, may indeed have come into existence after the evolution of proteins as enzymes.

Over the last few years analysis of rocks found in Antarctic ice sheets and originating from Mars contain microstructures consistent with leftovers of Martian organisms because these structures so closely resemble structures or leftovers from bacteria on Earth. The interpretation of whether these deposits are really proof of (ancient) life on Mars are controversial but of enormous interest to biologists. Single celled life on Mars, even if extinct today, would corroborate origin of life theories. Proven or not, the possibility of a future prove is enough to stimulate research including theory building on speculative grounds. It is these theories vaguely supported by experimental evidence (fossil evidence in this case) that will spurn imagination and the design of experimental protocols to actively explore the Martian soil and atmosphere. A note of caution; even if future analysis would prove that life existed on Mars, it would leave open the possibilities that life has been imported from Earth or life on Earth originated from Mars (or some place else). What ever the outcome, the current quest of proving the ancient existence of life on Mars at least gives an excellent example of how scientists work and draw conclusions from observations when events cannot be recreated in the laboratory under controlled conditions as is the case in studying the evolution of life.