15 November 2011

Not even close: 6 vs. 1,657,100,000,000

Genesis 1 lays out in a poetic manner a six-day sequence for the creation of the Earth. It's very simple, something I imagine an unschooled shepherd could easily deal with. 

19th Century geologists in Europe (especially England - the British Geologists Association formed in 1858) had watched as sediments accumulated in basins and puddles. They realized that they could rather easily calculate the rate of sediment accumulation. They also had seen and mapped huge stacks of similar, consolidated sediments in many places - and had even begun to correlate some distinctive bedding sequences in one place with bedding sequences a long ways away. This permitted British geologists, blessed with pretty much the fullrange of geologic ages on one small island, to figure out which layer sat on top of another layer, which must be older, and that units below these were older still.  By the turn of the 20th Century, even conservative geologists looking at their numbers had concluded that the Earth had to be many millions of years old. 

Geologists could also see another kind of time-line: progressively more sophisticated fossils, remains of ancient life forms not currently found walking or swimming the Earth, as the sediments got younger - more towards the "top" or modern day of the stratigraphic stack. A curator at the BYU Geology Museum once walked me through a series of dinosaur vertebrae, showing me how with time the vertebrae became lighter but at the same time structurally stronger. This meant they could run faster. Evolution.

Then Pierre and MarieCurieBecquerel, and others discovered radioactive decay. They could measure a decay rate for a given amount of a particular element, and they could see the daughter products forming as a result of that decay. It's an easy step to measure the ratio of radioisotope to its daughter products (uranium-lead, for example, and of course there are intermediate steps) and so you should be able to figure how long that particular crystal (a zircon, for example, containing uranium and lead) has been sitting there since it solidified out of a magma somewhere.  

WhoaGeochronologists started coming up with HUGE numbers. As more and more rock units were sampled and dated, the push-back for an oldest rock - homing in on an origin of the Earth - passed into the hundreds of millions of years, and then billions of years. 

Radiometric dating currently suggests that the age of the Earth is 4.54 +/- 0.01 years. 

Times 365 days per year, this is 1,657,100,000,000 days, at least, that this rock has been orbiting what is now our Sun.  This number is not really comprehensible to people who count on their fingers. "...7, 8, 9, 10!" Can you count higher than that? "Sure, (raises both hands overhead) "1, 2, 3, 4...".

However, as you consider the actual processes involved, as we understand them from geology and astronomy, it certainly can't be this precise. There was a protoplanetary disk, gravitational clustering, segregation, a crust formed, modified repeatedly by continued heavy early bombardment, and then later in the game there was an impact of another protoplanet that led to the formation of the Moon. So it's unrealistic to place such a precise three-decimal-point age as a "start" - better to point at the oldest piece of unmelted material ever found. The current record-holder comes from the Jack Hills of Western Australia, at 4.4 By.  If you compare the mass and luminosity of the Sun to other stars, and age-date meteorites, it is apparent that the Solar System can't be much older than that

Certainly there are complications with radiometric dating; the Carbon-14 creation rate in the atmosphere varies over time depending on cosmic ray flux, for instance. You can calibrate for this using tree-rings, however. Radiometric dating also must necessarily make some assumptions, among them that the decaying radioisotope and its daughter products remain together for the entire time that the age is calculated for (no remelting), and also that the decay rate today is the same now as it was when the original material solidified out of a melt. It's more complicated than that, even, but at this point we're only quibbling about small plus-and-minus stuff.

Science writing being as persistent as it is, rather few people take the Six Days of Genesis as literal truth these days. Genesis IS, after all, a translation of a translation, and the original writer had rather little experience with orbital mechanics, conservation of angular momentum, and the weak nuclear force. This is to say, he had a limited vocabulary to work with. 
In this context, I found some interesting things in the writings of Latter-Day Saint apostles who were also scholars: 

John A. Widtsoe wrote about the "vast periods of time" required for each class of animal to rise, dominate the Earth, and then become extinct. (Joseph Smith as Scientist, manual distributed by the General Board of the YMMIA, Church of Jesus Christ of Latter-Day Saints, 1908).

Here's something even more specific, unlike anything I've seen in any other church doxology: "What is a day? It is a specified time period; it is an age, an eon, a division of eternity; it is the time between two identifiable events. And each day, of whatever length, has the duration needed for its purposes." --Bruce R. McConkie, Mormon Church Apostle, during General Conference, 1982. 

I also was pointed at an interesting quote from the (atheist) astronomer Carl Sagan:

"How is it that hardly any major religion has looked at science and concluded “This is better than we thought! The Universe is much bigger than our prophets said, grander, more subtle, more elegant. God must be even greater  than we dreamed”? Instead they say, “No, No, No! My god is a little god, and I want him to stay that way.” A religion, old or new, that stressed the magnificence of the Universe as revealed by modern science might be able to draw forth reserves of reverence and awe hardly tapped by the conventional faiths. Sooner or later, such a religion will emerge." - Carl Sagan, "Pale Blue Dot:A Vision of the Human Future in Space" (1994).
I think that religion has emerged, actually. 

But let's put this all in perspective. Can you count to a million? Neither can I, so the difference between a million years and a billion years seems somewhat irrelevant - unless you are a geochronologist. I once poured over $250,000 into instrumentation for a rock-dating laboratory - because it was important to know how long ago a volcanic eruption had taken place, in order to get a sense of how dangerous that particular volcano was. That can be important, right? Especially if you live in, say Seattle, or Tokyo... or anywhere in the Mediterranean or Pacific Rim.

But consider this: allow for a minute the possibility that there is life after life. I have agnostic friends, even atheist friends, who go back and forth on this one. I myself have a number of strong experiential reasons for no longer questioning this. If you are an atheist, then the Age of the Earth doesn't matter. If you are faith-based, then... it doesn't really matter either. It's sort of like Pascal's Wager

When we die and make that transition, cross the Veil, I think there may be some questions asked of us. Like: Where is your family? What did you do to help others? 

Somehow I don't think that Someone is going to ask me "While you were in your mortal state, what was your opinion about the age of the Earth?"


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