Have you ever wondered if you could kick-start life on another planet? In the Origins of Life laboratory at McMaster University in Canada, there is a machine that allows you to try this very task.
Exactly how life began on the Earth remains heavily debated, but one of the most famous ideas was proposed by Charles Darwin in a letter to a friend in 1871:
“But if (and oh what a big if) we could conceive in some warm little pond with all sorts of ammonia and phosphoric salts…” Darwin began.
In contrast to the vast ocean, a pond would allow simple organic molecules to be concentrated and increase the probability of reactions that would form chains of longer molecules such as RNA; a single-stranded version of DNA that is thought to have been used for genetic information by the earliest forms of life.
It is highly likely that such warm little ponds would have the necessary ingredients to build such complex molecules. Experiments performed by Stanley Miller and Harold Urey in the 1950s demonstrated that water containing just the basic molecules of methane, ammonia and hydrogen would react to form a wide range of simple organics. Meteorites have also been found to contain similar molecules, proposing an alternative way of populating pools of water on the early Earth.
These ponds should therefore contain plenty of simple organics such as nucleotides, which stack together to form RNA. However, this stacking step turns out to be tricky.
“Anywhere where you have stagnant water and take sample, you will find organic molecules,” explains Maikel Rheinstädter, associate director of McMaster’s Origins Institute. “But you only find the building blocks, not the longer chains. Obviously, something is missing.”
In pond water, molecules are free to move around and potentially meet to initiate a reaction. The problem is that nucleotides carry a negative charge which repels the molecules from one another. While their motion is unconstrained, the nucleotides will therefore not approach close enough to react and form a longer molecule.
The solution is to dry out the pond.
As winter turned to summer on our young planet, shallow pools would have evaporated to leave the molecules suspended in the water lying on the muddy clay bottom.… Read more