why do scientist assume that the layers in ice core are annual?

Question

I have noticed many layers in the snow and ice in one winter in my own back yard. Is it possible they are rushing to a conclusion because they want to be right about global warming? was there not catascrophic weather hundreds and thousands of years before automobiles?

Answer 1

One of the limited resources is permission to engage atomic
Tom. The earliest records of atomic numbers were not measurables that had estimates. Ice being a visual element.
Let us assume it is actually not there unless the permission is
actively recorded by the natural client. A year is amendable.

Answer 2

Good observation.

Any excuse to prove their point of view. The people pushing global warming down our throats aren't really interested in facts, they are interested in manipulation.

Answer 3

Dating ice cores isn't the same as dating tree rings, it's not just counting of visual layers. Here's a discussion of the science behind it:

The basis of this method lies with looking for items that vary with the seasons in a consistent manner. Of these are items that depend on the temperature (colder in the winter and warmer in the summer) and solar irradience (less irradience in winter and more in summer). Once such markers of seasonal variations are found, they can be used to find the number of years that the ice-core accumulated over. This process is analagous to the counting of tree rings. A major disadvantage of these types of dating is that they are extremely time consuming.

Temperature Dependent
Of the temperature dependent markers the most important is the ratio of 18O to 16O. The water molecules composed of H2(18O) evaporate less rapidly and condense more readily then water molecules composed of H2(16O). Thus, water evaporating from the ocean it starts off H2(18O) poor. As the water vapor travels towards the poles it becomes increasingly poorer in H2(18O) since the heavier molecules tend to precipitate out first. This depletion is a temperature dependent process so in winter the precipitation is more enriched in H2(16O) than is the case in the summer. Thus, each annual layer starts 18O rich, becomes 18O poor, and ends up 18O rich.

This process also depends on the relative temperatures of different years, which allows comparison with paleoclimatic data. For similar reasons the ratio of deuterium to hydrogen acts the same way.

The major disadvantage of this dating method is that isotopes tend to diffuse as time proceeds.

Irradiation Dependent Markers
Of the irradiation dependent markers the two most important are 10Be and 36Cl. Both of these isotopes are produced by cosmic rays and solar irradiation impinging on the upper atmosphere, and both are quickly washed from the atmosphere by precipitation. By comparing the ratios of these isotopes to their nonradioactive counterparts (i.e. 9Be and 35Cl) one can determine the season of the year the precipitation occurred. Thus each annual layer starts 10Be and 36Cl poor, becomes 10Be and 36Cl rich, and then becomes poor again.

CORRECTION: I really mucked this one up. Although what is said above is true, this is an exceedingly minor effect. Both 10Be and 36Cl are formed as charged ions in the ionosphere. The Earth's magnetic field then traps them, with only a slight "leakage" of the isotopes to the lower atmosphere. The amount of "leakage" depends on the height of the ionosophere, which changes primarily in response to the Solar cycle, with periods of maximum solar activity corresponding to the highest extent of the ionosphere.

It should be noted that the 10Be/9Be ratios for some ice cores have been compared with the known solar cycle and are in excellent agreement with what is known (accurately showing the time of the European Little Ice Age, which corresponded with a remarkably low amount of solar activity).

The major disadvantage of this dating method is that these isotopes also tend to diffuse over time.

Using Predetermined Ages as Markers
In these methods, one uses the age of previously determined markers to determine the age of various points in the ice-core. The major advantage of these methods is that they can be completed relatively quickly. The major disadvantage is that if the predetermined age markers are incorrect than the age assigned to the ice-core will also be incorrect.

Previously Measured Ice-Cores
In this method one compares certain inclusions in a ice-core whose age has been determined with a seperate method to similar inclusions in an ice-core of a still undetermined age. These inclusions are typically ash from volcanic eruptions and acidic layers.

The major disadvantage of this method is that one must have a previously age-dated ice core to start with.

Oceanic Cores
In this method one compares certain inclusions in dated ocean cores with related inclusions found in the ice-core of a still undetermined age. Examples of such inclusions are a decrease (or increase) in temperature over a period of years that can be determined from flora and fauna found in the oceanic core and a decrease (increase) in the 18O enrichment over this same period of years. Another example is volcanic ash.

ADDITION: R. Hyde has posted separately some of the relationships between ocean core data and their astronomical causes. These are the primary "inclusions" that are compared. I apologize for my use of nondescript terminology here.

The major disadvantages of this method are that one must compare different signatures of climatic change that correspond to the same event and that one is not certain of the lag times (if any) between oceanic reactions and glacial reactions to the same climatic changes.

Volcanic Eruptions
After the eruption of volcanoes, the volcanic ash and chemicals are washed out of the atmosphere by precipitation. These eruptions leave a distinct marker within the snow which washed the atmosphere. We can then use recorded volcanic eruptions to calibrate the age of the ice-core. Since volcanic ash is a common atmospheric constituent after an eruption, this is a nice signature to use in comparing calibrated time data and an ice-core of undetermined age. Another signature of volcanism is acidity.

The major diasadvantage of this method is that one must previously know the date of the eruption which is usually not the case. Furthermore the alkaline precipitants of the ice ages limits this measure to approximately 8000 BC.

Ph Balances
One unique marker of periods of glaciation is that precipitation during the ice ages are markedly alkaline. This is due to the fact that the ice ages tied up a large quantity of the available water thus exposing a larger portion of the continental shelves. From these shelves huge clouds of alkaline dusts (primarily CaCO3) were blown across the landscape.

The major disadvantage of this method is that it gives only very approximate age ranges (i.e. this ice was laid down during the ice age). Furthermore, the lag time between the onset of glaciation and increased alkalinity are uncertain.

Paleoclimatic Comparisons
In this method, one compares long range climatic changes (e.g. ice ages and interglacial warmings) with markers (such as the 18O/16O ratios) found within the ice-cores.

Radioactive Dating of Gaseous Inclusions
In this method one melts a quantity of glacial material from a given depth, collects the gases that were trapped inside and use standard 14C and 36Cl dating.

The major disadvantage of this method is that a huge amount of ice must be melted to gather the requisite quantity of gases.

Ice Flow Calculations
In this method, one measures the length of the ice core and calculates how many years it must have taken for a glacier of that thickness to form.

This is the most inaccurate of the methods used for dating ice-cores. First one must calculate how the thickness of the annual layer changes with depth. After this one must make some assumptions of the original thickness of the annual layer to be dated (i.e. the amount of precipitation that fell on the area in a year).