Although I would love to believe that at one point there were behemoth like trees covering the Black Hills region, this is certainly not the case.
However I don't discredit those of you who believe for thinking outside the box, sometimes its good to look at things from different angles!
Now, as a former Geology major (later turned History major, who still harbors a love for rocks and geological processes) I feel like I have a unique
insight into the matter (although in reality I'm just supporting those who have debunked this theory in previous reply's).
Lets start from the top.
Here is an easy to read and convenient map produced by our friendly neighborhood US Geological Survey!
Blackhills Region Geology
Now that we can see what kind of rock formations exist in the area, we can examine the crux's of the giant tree argument.
1. The Petrified Tree Trunk Argument
Those who back the theory that these giant trees (or rather, trunks/branches) have been petrified over time don't seem to have the slightest idea of
how Petrification works. In order for Petrification to even begin, a very specific set of environmental variables needs to happen.
Firstly the tree/branches/twigs needs to be buried in an environment free of oxygen
(this is important) as oxygen is the free radical that
promotes decay in living organisms. The only strata that would create this oxygen free environment would be Volcanic Ash. Buried underneath, our
little tree/stick friend is safe and sound from decay. The second specific environmental variable is that a rich mineral water needs to flow through
the volcanic sediment, dissolving the silica within the sediment which then slowly enters and replaces the trees organic cellular structure (Quartz
Now that we know how the process works, I know some of you may still be thinking "Yeah that could totally happen to these massive trees, I mean, what
about the Petrified Forest?" and that actually brings up a valid point. However, that point will help prove why the petrification of these "giant
trees" is otherwise impossible.
If we are to operate under the maxim that these tree stumps/trunks/twigs are of/from a tree that is a 1/4 mile in diameter, to promote petrification,
we would need a volcanic eruption that can produce at least 15ft of ash (to cover some of the smaller outcroppings shown in the OP's links) or enough
ash to to pile up several stories to cover what some claim to be "tree trunks or stumps". Moreover you would also need a mineral rich constant flow of
water on top of that.
So those on the other side of this argument are assuming that at one point, the remains of these massive trees were covered in at least 1 story of
volcanic ash, mineral rich streams flowed over that volcanic ash and then years and years of erosion were able to uncover these giant plant monoliths.
This would be a highly unlikely event, considering that the only volcano able to produce even a fraction of the required volume of Ash would be the
Yellowstone Caldera, who only clears his throat about once ever 100,000 years, and can only produce anywhere between a 1 to 5 foot thick covering of
about 2/3rds of the continental U.S (which, although impressive is not adequate). This would not even begin to completely cover the outcroppings in
question. As far as I know, there is no geological record to support an anomalous ash-fall resulting in ash high enough to bury an 2 story (30 foot)
2. Trees with trunks around 1/4 of a mile wide.
Since this has already been addressed, I'm not even going to cover it.
So with those two arguments out of the way, that leaves us with the nagging question as to "What exactly are we looking at?"
1. Outcroppings of Sedimentary Rock!! (Or perhaps igneous?)
To me, a student of Geology, the formations shown in the pictures were clearly of sedimentary rock. However to others who have not studied this
subject, it would obviously be a source for questioning. I can't deny that some of these formations bare resemblance to a giant tree(s). With ridges
and layers very synonymous with that of tree bark (i.e. the Phellem, Phellogen and Phelloderm layers) . However, what we are truly looking at, and the
Map I shared earlier in my post supports this, is outcroppings of Sedimentary rock.
The ridges that look to be bark, are actually condensed layers of sediments that, under pressure create a molecular solid, chemically bonded rock. In
fact, if we go back many many years in Geological Deep Time (around the Devonin period), we know that much of Northern America was located very close
to the Equator, in what is now the Caribbean/Pacific-ish Ocean region. In fact, there were many regions that were actually submerged underwater! So,
as many aquatic crustations die and leave their calcified shells on the seafloor, we begin to get our first layers of sediment; as continental drift
and other geological processes happen, we end up with many many layers of sedimentary rock...who then get eroded by rains and continue the process. So
based on an approximation of the locations given, its likely we are looking at Sedimentary rock, or we could also be looking at volcanic Shale or
metamorphic Slate as there is indded a ring of crystalline igneous and metamorphic layers around Mount Rushmore.
Well anyway, there is my 2 cents I hope that helped you get an idea as to what is really going on in the region!
edit on 20-9-2013 by
GreenCross because: (no reason given)