We interrupt what was looking to be a reasonably pleasant week (at least in these parts) to announce that the ICR has returned to the old creationist gambit of “why haven’t the continents eroded already?” “Pleasant” having been replaced by the “hilarity” that last week seemed to lack, of course.
Today’s DpSU, from the Institute’s ‘Science Writer,’ Brian Thomas, is called Continents Should Have Eroded Long Ago. As I said, this is an old Creationist argument, but it is trotted out again because of the existence of a new erosion study. Let’s see what he’s got to say, and if it’s anything new…
According to standard evolutionary models, the earth is supposed to be 4.5 billion years old, and its continents supposedly formed 3.5 billion years ago. But if this is true, why haven’t earth’s landforms been completely eroded and deposited into the seas?
There’s the first problem – not all of the huge amounts of science that creationists disagree with have got anything to do with biology or evolution. Certainly not this. Chucking all of them together into one heap does not help people taking you seriously. But I digress – this is standard creationist mistake, and nothing out of the ordinary.
A new study indicates that the earth’s overall erosion rate, although slow, would have leveled the continents at least 70 times over if they are as old as the evolutionary claim maintains!
Geologists have been measuring quantities of 10Be, an isotope of the element beryllium that becomes radioactive with exposure to the sun. The more 10Be that is present at a given site, the longer it has been exposed to the sun without being carried off by erosion. This system was used by dozens of geologists to estimate erosion rates around the world.
But didn’t Mr Thomas tell us only a few weeks ago that all things radioactive are “Unreliable”? So much for that…
The “new study” is called Understanding Earth’s eroding surface with 10Be, from the GSA. Using this study to generalise over the entire earth is extremely questionable. They analyse readings taken from outcrops and basins across the world done by other researchers. You will note that they measure erosion in meters per million years. Numbers vary wildly – basins (which they found to erode more quickly) apparently have a mean of 218 m Myr−1, but a median of only 54 m Myr−1. For outcrops, the mean was still double the median (12 and 5.4 m Myr−1 respectively). One of the first things you learn when maths touches on stats is that when there is such a discrepancy between the “two averages” you’re treading on a minefield. Outliers – in this case, situations where mountains have more-or-less disappeared over night – are most likely the cause. Certainly you shouldn’t use it to say that everything should’ve eroded already, that geology is all wrong etcetera etcetera etcetera…
Judging by this quote – “The researchers…found that erosion occurs 18 times faster in drainage basins than it does in outcrops.” – Mr Thomas is using the outlier-affected means in his calculations (218/12 ≈ 18, while 54/5.4 ≈ 10).
According to the study, the average [again, mean] erosion rate for outcrops was 40 feet every one million years. The average thickness of continental crust above sea level can be estimated at about 623 meters, or 2,044 feet.2 To erode 2,000 feet of crust at 40 feet per one million years would require only 50 million years. So, if the earth is billions of years old, why is its surface not completely flat?
That’s really too much of a generalisation. basins and outcrops are only two kinds of surfaces open for erosion, and arguably they are the ones most prone to it. The more you erode an outcrop, the slower it will erode. Eroding a basin makes it flatter, and the study found that the flatter the basin the slower it erodes.
Continental basins, or low-lying areas that receive more rainfall from higher elevations, erode much faster. Applying this rate, continents would have eroded down to sea level in less than three million years. So the data in this study indicate that the overall time needed for continents to erode lies between three and 50 million years, a range that includes the 2007 estimate by ICR President John Morris of 14 million years.3
Remember, these aren’t the studies conclusions, they are Mr Thomas’.
But wait, aren’t eroded materials replaced by continental uplift? B.T. has an answer to that:
In order to maintain their belief in long ages, some might suggest that landforms were repeatedly uplifted by tectonic forces, providing more land mass for weather to erode. However, Loma Linda University [“a Seventh-day Adventist coeducational health sciences university located in Loma Linda, California, United States.”From wikipedia] geologist Ariel Roth noted that this scenario would have obliterated the very rock layers that supposedly represent evolution’s millions of years! He wrote:
It has been suggested that mountains still exist because they are constantly being renewed by uplift from below. However, this process of uplift could not go through even one complete cycle of erosion and uplift without eradicating the layers of the geologic column found in them. Present erosion rates would tend to rapidly eradicate evidence of older sediments; yet these sediments are still very well-represented, both in mountains and elsewhere.2
There is an important problem with this. That would be true if the replacement for eroded sediments came primarily from below. But it doesn’t. As far as I am aware, this is more-or-less what happens:
- Sure, mountains erode. Incidentally, the mostly erode into the basins, complicating the maths there significantly. And these basins too erode. But where does this stuff go? Have you ever heard of ‘deltas’? The point I’m trying to make is that a given piece of sediment can be eroded multiple times before it is lost completely, which makes Mr Thomas’ simple division rather pointless.
- When the stuff finally gets to the sea, it deposits there. Much of this sediment goes along for the subduction ride into the upper mantle, when it becomes magma.
- This is then deposited by volcanoes on top of what is there already. If nothing else, this slows the rate of the destruction of the sediment beneath, taking one for the team, as it were.
- And what of the stuff that doesn’t get subducted? It generally just sits there in shallow basins and similar, piling up layer after layer. It it here that most of the sediment that forms the geologic column that we go and dig up, having since been transported by the uplift of continents and mountains and then exposed by these very processes. Due to the ways that sediments deposit and erode, there is a serious bias towards ones that come from such seas. Why do you think there are so many good dinosaur fossils in the middle of the USA? There was once an inland sea there, which has never since subducted into anything, being technically on continental shelf and all. The full geologic column (particularly the early parts, which are much more rare than the higher portions) does not exist in its entirety everywhere, but it does exist.
- And, of course, the new rocks on the surface break down and erode in stages all the way back to the bottom of the sea.
- And is it too much to guess that the flatter and lower the continents, and the more sediment being subducted, the more volcanoes that will make their way up to the top, to deposit more fresh stuff on the surface. You couldn’t flatten the earth – it wouldn’t let you.
You may be wondering where the picture at the top comes in. It is of Mt Parícutin, a volcano that famously turned up in a farmers field in 1943. The picture is from the same year – it had certainly deposited a lot of stuff in a short time, far more than would have been eroded from the place if you could truly use those numbers to determine erosion across the world. And here is another picture, from just over 50 years later – that’s a big volcano!
As an aside, the Talk.Origins page on erosion mentions that the erosion claim directly contradicts another creationist claim, this time that:
Volcanoes are adding material to the crust too rapidly for an earth as old as is claimed. At present rates, volcanoes could have formed the entire crust in 500 million years.
Anything to disprove an old earth, eh?
I’d call this a Type AE – Misrepresented Study