Clay, what many think to be an infertile amalgamation of minerals, could conceivably have been host to a hotbed of life on Earth, as we know it. These assertions come in the wake of a recent study, the findings of which were published in the journal Scientific Reports by Nature Publishing.
A research initiative, spearheaded by researchers from Cornell University, aimed to explore the properties of clay in an ancient seawater simulation experiment. Under these conditions, the group discovered that clay forms a hydrogel. The clay hydrogel possessed numerous microscopic pores, capable of absorbing liquid, almost akin to a sponge.
There is currently no precise and limiting definition for the term hydrogel. However, the Encyclopedia of Pharmaceutical Technology defines it to be produced when a water-insoluble polymer absorbs a large amount of water. Within this structure, the hydrogel swells after absorbing large amounts of water, without dissolving.
The research team posit that these small spaces could have provided an ideal breeding ground for intricate chemical reactions to transpire, allowing synthesis of proteins, DNA and, ultimately, the development of highly specialized organelles that combine to form the cellular machinery. These small pockets could have provided adequate shielding to facilitate chemical processes, until the very first cell membranes started to form.
Professor of Biological and Environmental Engineering Dan Luo, who also belongs to the Kavli Institute of Cornell for Nanoscale Science, summarized his team’s hypothesis:
“We propose that in early geological history clay hydrogel provided a confinement function for biomolecules and biochemical reactions.”
Luo and colleagues elected to test this theory more extensively, through demonstration of protein manufacture within a clay hydrogel. The research team had previously employed synthetic hydrogels to show this process in action, adding all of the cellular ingredients necessary for protein synthesis, including DNA, amino acid building blocks and the correct enzymes needed for catalysis. Using this configuration – just as you would see inside a normal, membrane-bound cell – proteins encoded by the DNA stretches were successfully produced.
Synthetic polymer hydrogels were first discovered by a pair of Prague professors, Lim and Wichterle, who first synthesized the material and speculated its utility for biomedical purposes. It was found to be incredibly resilient across a broad range of temperatures and alkalinities, making it ideal for all manner of uses.
Synthetic hydrogels are still a relatively new and rapidly developing group of materials. Use of hydrogel substances varies wildly, from pharmaceutical and medical applications to agriculture. In ophthalmology, the material is used to create contact lenses, whilst its sponge-like properties are exploited during surgery for absorbable sutures. They have also been used for novel dressings, specifically designed to treat burns, and in tissue engineering techniques, drug delivery methods, and as durable coatings for biosensors.
For drug manufacturing processes, a great deal of synthetic hydrogel is required for these processes. A post-doc researcher, called Dayong Yang, observed that clay materials could be harnessed to form hydrogels. Luo argues that clay hydrogels are particularly useful for two principal reasons; they are incredibly cheap, and actually enhance protein production.
Carl Sagan, a now-deceased experimental researcher from Cornell, produced evidence substantiating the notion that a number of biomolecules were first formed within primordial oceans, channeling energy from volcanic vents and lightning.
However, the mystery over the exact mechanisms that were involved in driving these complex biochemical processes remains somewhat elusive. Researchers have desperately tried to fathom how these molecules could coalesce and assemble to generate more complex structures, whilst remaining protected from the environment.
Some scientists have alleged that polymers, or small bubbles of fatty materials, could have served as preliminary iterations of cell membranes. Clay hydrogel is a likely candidate for such a structure, since biomolecules are able to affix to their surfaces. This suggestion is strengthened by the finding that the cytoplasm behaves akin to a hydrogel substance, capable of providing partial protection to DNA from the catalytic activities of nuclease enzymes. The study literature discusses this point, at greater length:
“We noticed that the clay hydrogel inhibited nuclease activities, but did not inhibit the transcription/translation enzymatic reactions… we speculate that evolution might have already selected certain enzymes to be much more functional in the clay hydrogel environment than others.”
Furthermore, clay first appeared around about the same period that biomolecules began to form rudimentary cells (i.e. protocells).
Meanwhile, Luo and his research group remain committed to studying more about why clay hydrogel works so effectively, whilst definitively proving its historic function as the original hotbed of life. It is hoped that this research might be used to enhance cell-free protein production, and provide an even great array of applications for the material.
By James Fenner