Topic: Did Life Predate Earth? Extrapolating From Recent Evolution
smart2009's photo
Fri 04/26/13 12:32 AM
Basically, it posits that if life becomes more complex at a steadily exponential rate that can be extrapolated from recent evolutionary history, then life predates Earth.
In a thought-provoking paper published at arXiv (a non-peer-reviewed journal that’s a favorite of mathematicians and physicists for pre-press papers), Alexei Sharov, a staff scientist at the U.S. National Institute on Aging, and Richard Gordon, a theoretical biologist at the Gulf Specimen Marine Laboratory in Florida,examined recent increases in genetic complexity. They plotted “genome complexity,” measured by the genome size of majorphylogenetic trees, on a logarithmic scale over time. The resulting graph, shown above, determines that life gets doubly more complex about every 376 million years.
Sharov and Gordon said the relationship reminded them of Moore’s law, which describes how computers increase in complexity exponentially. Moore’s law holds that the number of transistors on a computer processing unit will double every two years (sometimes given as 18 months), accounting for an exponential growth in processing power.
If you use Moore’s law to extrapolate backward from modern computers, you’ll get back to zero in the 1960s, when microchips originated.
But if you apply the same logic to the genomic data (going back to a genome size of just a single DNA base pair) the equation doesn’t seem to square – life would have to originate around 9.7 billion years ago. TheEarth itself is only 4.5 billion years old. On its face, the graph seems to argue for the development of life on other planets -- did our pre-cellular ancestors ride here on the back of an asteroid?
There are several problems with this theory, though. The major one is that, obviously, we don’t have any 9.7-billion-year-old fossils to confirm what’s projected on the graph. As XKCD -- the popular nerdy webcomic -- illustrates, extrapolating beyondyour data can be a dangerous thing.
The “origin point” onthe graph, with a lifeform consisting ofjust a single DNA base pair, is also not really likely to have ever existed. Many scientists think that the early forms of lifeon Earth had genomes made of RNA, or possible some other kind of nucleotide.
What might really raise the eyebrows ofbiologists is the fact that Sharov and Gordon used genomesize as a measure of “genetic complexity.”The largest known genome on Earth belongs to either the amoeba Polychaos dubium (possibly 670 billion base pairs of DNA long, though this claim is disputed) or a rare Japanese flower called Paris japonica (149 billion base pairs of DNA). Humans (3.2 billion DNA base pairs) don’teven rank highest among vertebrates; that honor goes to the marbled lungfish,which has a genome made of 130 billion base pairs of DNA.
Also, Moore’s law of doubling complexity applies to the development of microchips; it wasn’t designed to describe the behavior of a messy biological process like evolution.
Evolution as we understand it now is not a linear path of developing complexity; the theory of punctuatedequilibrium assumes a more chaotic process full of spikes and dips. Short periods can see a furious radiation of evolution and speciation, thanks to a number of factors. A certain trait (like the ability to breatheair) could arise and allow organisms to colonize new territory, or some massive extinction event (like the asteroid blamed for the end of the dinosaurs) clears the board for a new set of species to take over. Some organisms change rapidly over the generations; others, like the coelacanth , are content to stay pretty much the way they are for millions of years.
“Is it reasonable to think that the complexity of life hasincreased at the same rate throughout Earth’s history?” the arXiv blog on MIT’s Technology Review wondered. “Perhaps the early steps in the origin of life created complexity much more quickly than evolution does now, which will allow the timescale to be squeezed into the lifespan of the Earth.”
SOURCE: Sharov et al. “Life Before Earth.”
http://www.ibtimes.co.in/articles/461497/20130426/evolution-moores-law-genome-moores-law-dna-moores-law-life-predate-earth-genetic-complexity-moores-l.htm

metalwing's photo
Fri 04/26/13 02:41 AM
It is NOT reasonable to think evolution has progressed at anything like a linear pace. There is tons of evidence to the opposite.

no photo
Tue 04/30/13 12:42 PM
We are the Martians

no photo
Sat 05/18/13 08:30 PM
There is probably life somewhere in the universe, perhaps not just in another space but in another time, in the distant past or future.....