by George Taniwaki
I recently came across a fascinating article with the novel claim that life is older than the earth. The argument is based on a regression analysis that estimates the rate of increase in the maximum genomic complexity of living organisms over time. (Note, this argument only makes sense if you believe that the universe can be more than 5,000 years old, that genes mutate randomly and at a constant rate, that genetic changes are inherited and accumulate, and that mathematics can be used to explain how things work. Each of those assumptions can be argued separately, but that is beyond the scope of this blog post.)
The article entitled Life Before Earth was posted on arxiv.org in Mar 2013. The authors are Alexei Sharov a staff scientist at the National Institute on Aging and Richard Gordon, a theoretical biologist at the Gulf Specimen Marine Laboratory.
They draw a log-linear plot of the number of base pairs in a selection of terrestrial organisms against the time when the organism first appeared on earth (see Fig 1). For instance, the simplest bacteria, called prokaryotes, have between 500,000 to 6 million base pairs in their genome and are believed to have first appeared on earth about 3.5 billion years ago. At the other extreme, mammals including humans, have between about 2.7 billion to 3.2 billion base pairs in their genome. The fossil record indicates the first mammals appeared about 225 million years ago, during the Triassic period. All other known organisms can be plotted on these axes and the trend appear linear, meaning the growth in genome complexity is nearly exponential.
Extrapolating the data back in time, one can estimate when the maximum complexity was only one base pair. That is, the date when the first protoörganisms formed. The trend line indicates this occurred 9.7 billion years ago, or about 4 billion years after the big bang.
Figure 1. The growth in maximum base pair count per genome seems to grow exponentially over time. Image from arxiv.org
The earth is estimated to be only 4.5 billion years old. Thus, if these results are accepted, the implications are pretty astounding.
1. Life did not start on earth. It started somewhere else in the galaxy and reached the microörganism stage. Through some cosmic explosion, the life was transported here. Alternatively, life started on one of the planets around the star that went supernova before collapsing and forming our present-day sun. This hypothesis is called exogenesis
2. It is unlikely that these alien microörganisms only landed on earth as our solar system formed. They probably coated every asteroid, comet, planet, and moon in our solar system. They may still be alive in many locations and are either evolving or dormant
3. If all of the microörganisms that reached our solar system came from the same source, they likely have the same genetic structure. That is, if we find life elsewhere in our solar system, it is likely to contain right-handed double helix of DNA using the same four left-handed amino acid base pairs as life on earth. With effort, we could construct an evolutionary tree that contains these organisms
4. In fact, the same microörganisms may be very common throughout the galaxy, meaning life has arrived on many other planets, or perhaps every planet in our galaxy, even ones with no star, a hypothesis called panspermia
5. It solves Fermi’s paradox. In 1950, Enrico Fermi noted that our Sun is a young star and that there are billions of stars in our galaxy billions of years older. Why haven’t we already been contacted by intelligent life from other planets? The answer based on this analysis is because intelligent life takes 9.7 billion years to form and we may be one of the first organisms to reach the level of intelligence necessary to achieve intentional interstellar communication and travel. Ironically, if Sharov and Gordon are right, unintentional interstellar travel is already quite common and has been for billions of years.
Relationship to Moore’s Law
If the exponential growth of complexity shown in Figure 1 above looks familiar, it is because it is the same shape as the increase in the number of transistors in microprocessor chips over time, a relationship called Moore’s Law. The authors cite this analogy as a possible argument in favor of their case.
Figure 2. The growth in maximum transistor count per processor has grown exponentially over time. Image from Wikipedia
Is this reasonable?
Like I said, this is a fascinating article. But it is all speculation. We have no direct evidence of many of the claims and inferences made in this paper. Specifically, we don’t know:
- The exact size of the genome that various organisms had in the earth’s past
- The nature of possible organisms less complex than prokaryotes
- The existence of any alien microörganisms or evidence that any landed on early earth
- The speed of genetic complexity changes in the early earth environment, or on other planetary environments in the case of the alien microörganisms prior to arrival on earth
- Whether any modern earth organisms, or any potential alien microörganisms, could withstand the rigors of travel through space for the millions of years it would take to get to earth from another star system
Finally, we have no clear explanation why the rate of change in genome complexity should be exponential. The use of the Moore’s Law chart to show that exponential growth in complexity is reasonable is slightly disingenuous. Moore’s Law is generally used as a forecast for the future growth in complexity for a commercial product based on historical data. Further, the forecast is used to estimate product demand, research costs, and necessary production investment, all of which tends to drive advancements and make the prediction self-fulfilling.
On the other hand, genome complexity is not directed. Evolution is a random process that will generate greater complexity only if a new, more complex organism can take advantage of an ecological niche that cannot be exploited by simpler organisms. Nothing is driving greater genome complexity.
Anyway, this is a very controversial theory. But I believe it may lead to new insights regarding microbiology, astrobiology, molecular clock hypothesis, and the use of mathematical models in evolutionary biology.
How long is 13.7 billion years?
As a side note, sometimes we wonder, how could something as complex as DNA and cellular organisms have started from nothing? It seems impossible to comprehend. But if you take a look at Figure 1, you will see that it may have taken over six billion years for a single base pair of DNA to grow in complexity to form an organism that we think of as a simple, primitive prokaryote. Then it took another 3.5 billion years before mammals appeared. Then it only took 200 million more years before our human ancestors appeared. And finally only a few hundred thousand years passed before you and I were born.
To give you a feel for how long 13.7 billion years is, watch this extremely boring YouTube video that compresses each billion years into one minute increments.
Figure 3. Age of Universe, boring, even with music. Video still from Craig Hall
A final thought to close this blog post, there may be aliens living on earth, but don’t be afraid, because it’s us.