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Thylakoids are little pouches located in the chloroplasts of plants. They store chlorophyll, the substance in plant that reacts to sunlight and triggers photosynthesis. They are found in ancient, light-sensitive bacteria called cyanobacteria. The latter, multiplied in the oceans billions of years ago, and are believed to be responsible for the vast stores of oxygen that are found in the atmosphere and thus, a precursor to life as we know it. However it is now believed that thylakoid membranes in cyanobacteria were what made them capable of using sunlight to create energy and release oxygen.
The oldest known fossil thylakoids date back to around 550 million years. Researchers at the University of Liège, Belgium have identified microstructures in fossil cells that are 1.75 billion years old. These thus become the oldest thylakoid membranes, ever found. The discovery of preserved thylakoids in an ancient microfossils, called N. Majensis, of the coasts of Australia, providesdirect evidence of a minimum age of around 1.75 billion years for the divergence between cyanobacteria with thylakoids and those without. The recent discovery also raises the possibility of discovering thylakoids in even older cyanobacterial microfossils, and to test the hypothesis that the emergence of thylakoids may have played a major role in the so called ‘Great Oxygenation’ of the early Earth around 2.4 billion years ago. Around that time, the oxygen released by cyanobacteria, filled the ocean and made its waters oxygen rich. Over time, this oxygen started escaping into the atmosphere, where it reacted with methane. As more oxygen escaped, methane was eventually displaced, and oxygen became a major component of the atmosphere. This event is known as the Great Oxidation Event.
