Reading extra material about the origins of life
The paragraph is about ideas around how life might have got going on Earth. It could be something you have found in a book you have picked up in the library.
In the 1950s interest in self-replicating units and the chemicals from which they are made was stimulated following a famous experiment by Miller & Urey at the University of Chicago. They set up what was effectively a sealed model of the Earth’s early atmosphere – which they thought to be methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O). They passed an electrical discharge through it to simulate lightning. After about a week they found that some complex organic molecules, including amino acids (components of proteins), had been formed. It suggested that life could have erupted spontaneously on Earth simply through a chance coexistence of the right precursor molecules and the right environmental conditions. Numerous more complex experiments followed, confirming and extending Miller & Urey’s original results. But there were many critics who argued that that the atmosphere in the experiments was wrong or that the continuous electrical discharge did not reflect the real action of lightning. In some ways, these experiments have only added to the uncertainty of the origin of life on Earth, as has the discovery that many of the organic compounds created in these experiments can also be found in meteorites that have arrived on Earth from deep space. Other theories abound: it has been suggested, for example, that the unusual environmental conditions found in the vicinity of deep-sea hydrothermal vents could be suitable for the creation of complex organic compounds. Another possibility, however unlikely it sounds, is that the ice/water layer beneath sea ice, might provide a stable platform for the required chemical activity. The reason is that the deep sea and the region beneath the polar ice is well protected from harmful UV light, levels of which would have been very high before oxygen and hence ozone was present in the atmosphere.