Evidence of the earliest life forms based on secular science
One cornerstone for our estimate of early life is seen in the stromatolites, which represent ancient cells. The oldest “stromatolites” reported are from rocks of Isua Supracrustal Belt, Greenland, dated at 3,750 million years (Ma) ago, but they have been questioned as to whether they can really be considered as the first imprint of life. More solid data exist about formations that are 3,500 Ma old containing remnants of ancient cells: (i) One is the Pilbara region of Western Australia with an age of 3,430 Ma; a recent report supports the suggestion that these Pilbara-Craton structures might be of biotic origin.3 (ii) Another of about the same age with evidence of microbial biomarkers is the pillow lava from the Baberton Greenstone Belt in South Africa.4 Such ancient cells must have genes (from RNA?) and a translational apparatus, i.e., the genetic code has an age of 3.2 to 3.6 billion years. This estimate has been backed up in an elegant study of Eigen and coworkers,5 where tRNA sequences from various organisms were used to conclude that the genetic code has an age of 3,300 ± 300 Ma. It follows that chemical evolution, the development of the genetic code and the existence of the “RNA world” must be squeezed into a time span of 400 to 800 Ma, corresponding to the time gap between the formation of the first rocks (4,000 Ma) and the appearance of the first cells (3,600 to 3,200 Ma). Another important landmark is the observation, in many iron deposits around the Earth at the geological layer of about 2 billion years ago (2,000 Ma), of FeIII (ferric state) precipitates indicating the appearance of the oxidizing power of O2, a product of photosynthesis. The earliest FeIII deposits are found in the Hamersley iron formation in Western Australia.6 At deeper layers, FeII (ferrous state) deposits are usually present. It follows that cyanobacterial photosynthesis developed before 2,000 Ma. Appearance of the pollutant O2 in the atmosphere was a major threat to early life, since every cell contained and still contains a reducing milieu—a relic of the origin of life when the atmosphere was reducing. The consequence was obviously a massive extinction. Only a few cells survived due to a membrane composition that prevented the passage of oxygen into the cell. Over the long run the cells eventually turned the appearance of atmospheric oxygen into a major advantage by inventing respiration.
One cornerstone for our estimate of early life is seen in the stromatolites, which represent ancient cells. The oldest “stromatolites” reported are from rocks of Isua Supracrustal Belt, Greenland, dated at 3,750 million years (Ma) ago, but they have been questioned as to whether they can really be considered as the first imprint of life. More solid data exist about formations that are 3,500 Ma old containing remnants of ancient cells: (i) One is the Pilbara region of Western Australia with an age of 3,430 Ma; a recent report supports the suggestion that these Pilbara-Craton structures might be of biotic origin.3 (ii) Another of about the same age with evidence of microbial biomarkers is the pillow lava from the Baberton Greenstone Belt in South Africa.4 Such ancient cells must have genes (from RNA?) and a translational apparatus, i.e., the genetic code has an age of 3.2 to 3.6 billion years. This estimate has been backed up in an elegant study of Eigen and coworkers,5 where tRNA sequences from various organisms were used to conclude that the genetic code has an age of 3,300 ± 300 Ma. It follows that chemical evolution, the development of the genetic code and the existence of the “RNA world” must be squeezed into a time span of 400 to 800 Ma, corresponding to the time gap between the formation of the first rocks (4,000 Ma) and the appearance of the first cells (3,600 to 3,200 Ma). Another important landmark is the observation, in many iron deposits around the Earth at the geological layer of about 2 billion years ago (2,000 Ma), of FeIII (ferric state) precipitates indicating the appearance of the oxidizing power of O2, a product of photosynthesis. The earliest FeIII deposits are found in the Hamersley iron formation in Western Australia.6 At deeper layers, FeII (ferrous state) deposits are usually present. It follows that cyanobacterial photosynthesis developed before 2,000 Ma. Appearance of the pollutant O2 in the atmosphere was a major threat to early life, since every cell contained and still contains a reducing milieu—a relic of the origin of life when the atmosphere was reducing. The consequence was obviously a massive extinction. Only a few cells survived due to a membrane composition that prevented the passage of oxygen into the cell. Over the long run the cells eventually turned the appearance of atmospheric oxygen into a major advantage by inventing respiration.
