MIT’s technology review has a though provoking snippet on the origin of life. Alexei Sharov & Richard Gordon have published a paper (a copy can be seen here) that uses the concepts of Moore’s Law to extrapolate back in time to predict the date at which life first emerged.
Moore’s law states that the number of transistors on a circuit doubles every two years, leading to an exponential increase in the number of transistors on a microchip through time. If you graph the increase today on a log scale and extrapolate backwards, the line crosses the zero axis in the 1960s, when transistors were indeed born.
Interestingly, the same process can be applied to scientific publications. Between 1960 and 1990 the number of science papers doubled every 15 years or so. Graphing this and extrapolating back takes you to 1710. Isaac Newton’s Philosophie Naturalis Principia Mathematica was published in 1687, with additional editions in 1713 and 1726.
Sharov and Gordon applied this to life itself, using the complexity of the genome and known fossil events as data points. They suggested that the genome size doubles every 376 million years, give or take.
So, using Sharov and Gordon’s technique, when did DNA originate? Their thought provoking extrapolation came up with an age of around 9 ½ billion years. That’s about 5 billion years older than the Earth.
Like all good analysis, this work raises many more questions than it answers.
For instance, applying Sharov and Gordon’s technique to human population growth yields the first human at about 0AD, which is clearly wrong. This is because the human population bumbled along, not doing a great deal, until quite recently, hitting its real exponential and stratospheric stride with the technological and health advances of the Industrial Revolution. So trends can change…
The ancient date also raises questions about the early Earth. The young Earth is envisaged as a hell-like volcanic surface of mixed molten rock and patchy crust. In fact, the geologic age is named the Hadean (4000-4500Ma). Collisions with other solar bodies such as asteroids, comets, and small planetoids were common, with an intense period called the Late Heavy Bombardment between 4,100 and 3,800Ma. The moon is believed to be the result of such an impact, in which a Mars side planet collided with the Earth. Surprisingly, it is possible that water existed on this hellish surface, even though the surface temperature was >230 Celsius, as the atmosphere was likely thick with CO2 and the pressure would have kept the seas from boiling. The first direct evidence of water is from between 4.4 and 4 billion years ago, recorded in detrital zircons. The end of the Hadean is marked by the emergence of a fully solid surface, with plate tectonics, and rainfall driven by volcanism.
The earliest potential evidence for life is from Australia, where fossils that appear to be simple stromatolites are found in rocks 3.5 billion years old, but some contest their organic origin. The first uncontested fossils are microfossils and chemical traces in rocks that are 2.7 billion years old, almost 2 billion years after the formation of Earth.
So, there are some interesting issues regarding the technique, and some of its implications, but Sharov and Gordon’s paper does re-ignite the concept of panspermia.
Did life arrive from outer space?