In response
to John and his November, 2002, feedback entitled 'Re
Greenland ice core project:', I would like to offer a more
detailed response.
The most obvious way to observe present-day accumulation
of Greenland snow and ice is to lay a marker, like a
one-meter square piece of stiff plastic on the surface, and
come back one year later and collect a one-square
centimeter column of snow and ice on top of it. Then by
melting the snow and ice, and measuring the height of the
equivalent one-square centimeter column of water, you know
what the annual accumulation was, in an equivalent
thickness of water. Other kinds of markers can be used, but
I think you get the idea.
This has been done for many, many years. The average
equivalent accumulation over the last 150 years, or so, is
about 0.25 meters of equivalent water. (See 'Snow
Accumulation at GISP2 Summit, Greenland' ) This number
can be compared to visible layering in the snow and ice,
especially the top layers where annual measurements have
been made. By direct observation one visible layer is one
year's worth of accumulation.
Individual visible layers have been counted downward
with slightly increasing uncertainty as you go deeper. (See
GISP2, on-line
which discusses the conservative age error estimates of
+/-2% from 0 to 11.64 kyrs, +/-5% from 11.64 to 17.38 kyrs,
and +/-10% from 17.38 to 40.5 kyrs, Alley, et. al. 1993; or
on the CD-ROM available from the National Snow and Ice Data
Center, University of Colorado at Boulder, and the World
Data Center-A for Paleoclimatology, National Geophysical
Data Center, Boulder, Colorado.) But down to a depth of
about 1680 meters in the borehole named GISP2 the
individual layers counted stand at 11,640 and that count is
quite accurate. (See
GISP2 Layer Counted Timescale and the Meeser/Sower
official GISP2 timescale discussed on
A Note on the Timescales.) This point in time,
approximately 11,640 years before 1950 A.D., marks the end
of the event called the Younger Dryas. This event is the
global weather phenomenon used to delineate the transition
from the Pleistocene Epoch to the Holocene Epoch, the
Holocene being the geological time period we live in today,
also called the Recent. It is a very illuminating exercise
to plot various different data logs from the GRIP and GISP2
boreholes and observe this climatic event leaving its mark
on so many of them.
Greenland is covered by a continental glacier that is
3,000 meters thick at the 'continental divide' or the
'summit,' being the approximate geographical center.
Deposition of ice has been recorded in the recent past and
continues today. In analogy to geological sedimentation,
the oldest deposition is at the bottom and younger
deposition sits on top, becoming progressively younger from
bottom to top. In Geology this is known as Steno's Law of
Superposition, first explained in print by the Dane,
Nicolaus Steno, in the late 1600's. Some Young-Earth
Creationists deny this simple, logical premise with regard
not only to the Greenland ice but to all of Geology as
well. (See 'Those
Remarkable Floating Rock Formations'.)
If there are any physical differences in the ice as one
descends through the depths, then those physical
differences might be able to be used to date the ice and to
discern something about Earth's climate over that time
period. Boreholes have been drilled, and cores have been
recovered. (Core drilling uses a cylindrical drill bit that
cuts a circular ring of material away while leaving the
interior material undisturbed. At certain intervals, like a
few meters, this 'core' is broken at its base and
physically removed up the borehole to the surface where it
is preserved for study.)
A host of physical measurements have been made both in
the boreholes and on the cores. These include visual
observation of layers, electrical conductivity,
concentration of various chemical ions, concentrations of
Deuterium, concentrations of Oxygen isotopes, Carbon-14
dating of entrapped carbon dioxide, volcanic ash, borehole
diameter, borehole orientation (boreholes are not perfectly
vertical nor perfectly straight), temperature, and
more.
Layering is visible in almost all of these logs.
Deuterium and Oxygen isotope concentration logs, for
instance, depend upon the surface temperature of the oceans
from which the water came. During evaporation the seasonal
differences in surface temperature make for different
partial pressures of water composed of Oxygen-18 and
Oxygen-16, and between common water molecules with Hydrogen
and molecules with one Deuterium and one Hydrogen. The
process of depletion of one isotope at a higher rate than
the other continues to depend upon the temperature of the
water as it travels from the ocean to the Greenland Summit.
Summers are warmer and winters are colder, even in
Greenland. Thus we see a record of seasonal temperature
variations in the two different isotope concentration logs
- Oxygen-18 vs. Oxygen-16, and Deuterium vs. Hydrogen. (See
GISP2 Bidecadal Oxygen Isotope Data and Deuterium data
cited below.)
The Deuterium log has been recorded at high resolution
in GISP2 down to a depth of 194 meters, with an age of 680
years, or 680 warm-cold cycles, with an average sampling
interval of about 3 centimeters, and about 16 samples per
warm-cold cycle near the top, and about 9 samples per
warm-cold cycle near the bottom. (See GISP2 Stable Isotopes
(Deuterium) data file deltad.dat available on-line at
GISP2 Stable Isotopes (Deuterium, High Resolution).)
This data shows that there are no higher 'frequencies' of
warm-cold cycles in the the ice, higher than one cycle per
annum. These highly detailed warm-cold cycles correspond to
the visible layers. This is another, independent
confirmation that one visible layer is one annum.
Using the best available methods and the best available
data for layer counting and for determining the time period
for each layer, scientists have developed a time scale for
the Greenland ice cores. The ice is more than 100,000 years
old at the base. (See the Meese/Sower timescale,
GISP2 Meese/Sowers Timescale, for time of deposition
versus depth in GISP2 and
GRIP Depth Age Scale from Flow Modeling for time of
deposition versus depth in GRIP based upon flow
modelling.)
Young-Earth Creationists oppose the interpretation of
the Greenland ice cores as a continuous record of Earth's
climate for the past 100,000 years, or more. If true then
these ice cores, and the logs of various data recorded from
the boreholes and from the recovered cores themselves,
offer positive evidence that the Earth is at least 100,000
years old and certainly not less than 10,000 years old as
the Young-Earth Creations insist.
Young-Earth Creationists attempt to discredit the
Greenland ice cores at all costs because they destroy the
very foundation of their belief in a young Earth.
One way they attempt to discredit the Greenland data is
to insist that the layers are not annual layers but
individual storms that occur more frequently that once per
year. Never mind that the layering in the Oxygen isotope
and Deuterium logs represent alternating warm and cold
deposition. (Why would many tens of thousands of storms
alternate between one warm storm and one cold storm for so
many thousands of storms in a row? The Young-Earth
Creationists respond by saying that the physicists must
have gotten it wrong. There must be another explanation for
the layers other than warm/cold deposition. Perhaps there
was evaporation between storms, they argue in desperation.)
They simply distrust the layer counting as annual layers
and say "we just don't know" when asked to explain how the
layers came about.
When presented with demonstrable evidence that
present-day deposition is precisely equivalent to visible
layering near the surface (and therefore one layer per
year) they insist that in the past there must have been
more than one visible layer per year. They offer no
explanation of how this could have happened.
Young-Earth Creationists deny the efficacy of
radiocarbon dating. They throw out the age dating of the
ice from entrapped carbon dioxide. Because one radiocarbon
date may have been wrong once in the past (due to perfectly
well-known reasons, it should be noted) they throw out all
radiocarbon and all radioisotope dating. (The radiocarbon
dates of the Greenland ice agree with the layer-counting
dates but are almost always a few hundred years younger.
The carbon dioxide in the atmosphere circulates down into
the firn until the firn becomes ice and entraps the carbon
dioxide.)
Young-Earth Creationists deny the correlation of the
Greenland ice cores with known volcanic eruptions. They say
that the record of the ash in the ice shows peaks where no
one can name a corresponding volcano, and shows no peaks
where volcanoes are known to have occurred. Thus
correlation with volcanoes cannot be trusted. They ignore
the multitude of positive correlations of known volcanic
eruptions with ash in the Greenland ice.
Another way to discredit the accepted Greenland ice
dating is by seeking independent evidence of the age of the
ice without reference to other methods. This line of
investigation is a valid means of research. But it is easy
to misuse, to misconstrue, and to arrive at conclusions
that will not stand up to critical scientific analysis.
One Young-Earth Creationist, with a Ph.D. in Physics,
has published on a creationist website a document arguing
that the Greenland ice is younger than scientists claim.
(See 'Ice
Cores and the Age of the Earth'.) His argument depends
upon the World War II airplanes found buried in the ice
recently. He demonstrates how their depth, divided by their
known age, corroborates a young age for the ice, without
considering the sinking of the airplanes into the ice and
the thinning of the layers deeper down as the ice flows
toward the sea. Then he applies an overly simplistic, and
improperly chosen, average of the layer thinning observed
from a coastal borehole to the thickness of the summit ice
in order to compute a slightly older, but still young, age
for the ice.
Strangely he says his calculations are in good agreement
with annual layer counting but fails to mention that there
are about 12,000 annual layers down to a depth of about
1,700 meters in the ice, increasingly thinner with depth on
average. How many more annual layers are there in the lower
1,300 meters of ice? More than 12,000 to be sure. Layers
become increasingly more difficult to count individually
with increasing depth, but in the lower 1,300 meters of ice
it is estimated, based on good science, that there are at
least 98,000 additional annual layers. The Creationist
mentions none of this.
As a physicist he should know that the ice near the
surface, called firn, is riddled with air-filled pores and
is much less dense than solid ice. As a physicist he should
know that airplanes are much more dense than firn, or ice,
and that they sink with time. As a physicist he should know
that simplistic computations on data from the edge of a
glacier (averaging values from the surface and 'near the
bottom' instead of applying integration and curve fitting)
should not be applied to the center of a continental
glacier hundreds of kilometers away.
His computation of the short number of years needed to
deposit more than 3,000 meters of Greenland ice is an
extrapolation of his faulty annual deposition, overly
simplistic math, and his failure to recognize that glacier
edges are different from continental glacier centers.
It strains credulity that a Doctor in Physics can
overlook these errors. Such is the scholarship, or
integrity, of Young-Earth Creationists.
