One of the big scientific questions is how life began on earth. Many scientists are now agreed that life is almost certain to have originated out of simpler, chemical compounds. Further, that this is practically inevitable given the early conditions on earth. This isn’t about faith, but the evidence that has been accumulated.
Since the Miller experiments of the 1950s, the application of the principles of chemistry and physics to this problem has shown that nearly all the components of a simple-cell can and do form naturally.
The evidence can be summarised as:
- Environmental - There are several conditions that must apply to make chemical evolution possible. First, there has to be an external energy source*. Prebiotic earth has lots of these- lightning, volcanoes, radiation. Second, we can’t have a lot of oxygen. Lots of oxygen will make any formed complex molecules short-lived. Again, prebiotic earth had little atmospheric oxygen. Third, there has to be the chemicals available for life around to work with. That means 6 indispensable macro-elements- C, H, O, N, P and S have to be around. Again, these are known to be present.
- Why not Panspermia? Every cell of every organism is remarkably the same at an elemental level. It doesn’t matter if we are looking at fungi or fish or humans. The percentages of the macro-elements above are very similar. This is exactly what we’d see if life started by using the available chemicals on earth. In fact, the proportions of elements in every organism aligns most closely to river water. This supports abiogenesis occurring here on earth, and is a smoking gun for a natural origin of life.
- Forming complex molecules- the environmental conditions above are necessary for abiogenesis but not sufficient to show its feasibility. Since the Miller-Urey experiments of the 1950s, we have shown that the building blocks of a cell will occur naturally. We have shown that amino-acids, sugars, RNA/DNA bases, hydrocarbons, phosphate esters, peptides etc will all be formed under the right abiotic conditions. The 8 amino-acids that dominate these abiotic conditions are also those most common in proteins. This is another ‘smoking gun’ that life began from abiotic conditions on earth.
- The Proto-cell - A cell is basically a package of organic & inorganic molecules surrounded by a double-lipid membrane. We have shown small double-lipid membranes will form in small vesicles that surround organic molecules (since the experiments of Fox in the 1970s). In fact, it is remarkably easy to generate these.
- Replicating molecules. Life also needs molecules to be able to replicate. This is also a natural chemical phenomenon. In 1996 the jounal Nature reported the discovery of a self-replicating alpha-helical peptide. This had a 32-amino-acid sequence, and interestingly, had several dipeptides found in the membrane proteins of ancient archaebacteria.
The scientific evidence is consistent with and supports an origin of life on earth out of abiotic conditions. There has been no chemical, biological or physical law that has been discovered in this research that would prevent life emerging. We have discovered so much about the processes of this chemical evolution that recreating life in the test-tube now looks feasible.
Of course, we should for completeness consider the evidence for a divine creator or intelligent designer. I’ve made a list, but it’s blank.
* The external energy sources for abiogenesis is why Pasteur’s experiments on spontaneous generation don’t apply. Pasteur looked at a closed thermodynamic system. Abiogenesis is about open thermodynamic systems. In order for complex molecules to be formed, local entropy has to be reduced and this is only possible in open-energy systems.