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The evidence seems to suggest that all life on Earth has developed from a single organism back in the mists of time, and perhaps even from one single common ancestral cell. Current thought suggests that the “last universal common ancestor” (the hypothetical latest living organism from which all organisms now living on Earth descend, or, in other words, the most recent common ancestor of all current life on Earth) is estimated to have lived some 3.5 to 3.8 billion years ago. However, the actual mechanism for its origination is still far from clear.

While the circumstances that led to life on Earth are no doubt special, there is no reason to suspect that they are peculiar to Earth. As Richard Dawkins points out, if the universe contains a billion billion planets (which some scientists consider a conservative estimate), then the chances that life will arise on one of them is not really so remarkable. If, as some physicists claim, our universe is just one of many in a multiverse, each of which contains a billion billion planets, then the chances that life will arise on at least one of them is almost a certainty.

Indeed, many scientists believe that it is entirely possible that different forms of life may have appeared quasi-simultaneously in the early history of Earth. Some of these may now be extinct, or they may survive as extremophiles (an organism that thrives in extreme conditions that are detrimental to the majority of life on Earth), or they may simply have gone unnoticed. It is only in quite recent years that living things have been discovered in conditions as unlikely as hot volcanic vents deep beneath the sea and in totally dark and dry lava tubes in the desert.

As science progresses, there is even the possibility - or the specter, depending on your outlook - of one day creating man-made life. Harvard scientist George Church for example is hot on the trail to building a completely man-made living cell. He has identified a total of 151 essential components which he believes represent the minimum for the creation of life - a sort of blueprint for life itself - and has been making rapid progress in synthesizing them in the laboratory.

This remains an area of intense debate and speculation in both scientific and religious circles and, while new discoveries are made almost every year (which may, or may not, throw some light on the subject), no definitive solutions have yet been yielded.

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