Passing through the forest and noticing the old stump, the inquisitive person will certainly stop and pay attention to the mossy cut of the tree. What does he remember? What could I tell by finding a voice? Having wiped the moss cover off, it is easy to notice circles crossed out by cracks. Tree rings can tell a lot. About the youth of the plant, about its life cycle, about cold cold and about hot, dry days. Before the eyes of knowledgeable people reveals year after year, decade after decade. This science was born recently, it is called dendrochronology.
The concept of dendrochronology
The study of cross sections is not difficult. A section of a tree is examined under a microscope, each annual layer is measured in millimeters. According to measurements, a special schedule is drawn up, it indicates the change in the thickness of the rings. The graph creeps up, if the thickness of the rings is wider (years favorable for the tree), the graph decreases when the years were dry and heavy. After analyzing the fresh cut of the tree, and building a graph, you can get a chronicle of his life, testifying to the weather conditions during the life of this plant, that is, the last years of our time. Having found a saw cut of an ancient tree in the forest, you need to do the same work and get a schedule. On it it will be possible to judge the weather conditions of the period in which it grew. So year after year you can delve into history.
But not so simple. In European forests, ancient trees do not survive more than three hundred to four hundred years, unless the oak sometimes reaches half a millennium. But it is very difficult to study a cut of a deciduous tree. Vague rings reveal secrets very reluctantly. Scientists in America were in a better position. There, some trees lived a millennium. These are some gymnosperms, yellow pine, Douglas fir. Alpine pines that have lived four and a half thousand years have even been discovered. During excavations at the place of the Indians' dwelling , saw cuts were found, according to which it was possible to compile dendrochronological charts for a whole millennium.
Annual rings. Research in Russia
For many years, scientists have studied only the wood of America. Europe turned out to be a white spot in this area. Only after the war in Russia, scientists began to search for ancient saw cuts. Favorable for the study of the northern regions. The soils here are well moistened, and the frozen ground perfectly preserved many tree trunks. Scientists gathered a huge "harvest" of wood during excavations in ancient Novgorod. Here, several thousand very different breeds were discovered, layered on each other at different depths. Layer after layer, scientists have uncovered archaeological material: risers of churches, log flooring, log houses. Finds were found at an eight-meter depth. But how could the age of scattered finds be related? Slices of the tree trunk were prepared with more than three thousand specimens. Each breed had to build its own dendrochronological scale.
Dendrochronologists have done tremendous work. They didnโt just line charts. In order to establish a reference schedule, I had to study the entire history of the ancient city, the annals, determine in which year this or that wooden structure was erected.
Aegean Dendrochronological Project
Work in the high-profile Aegean dendrochronological project has been ongoing for 35 years. Its purpose is to create an absolute dendroscale for the Middle East and Aegean regions, inclusive from the trees of the first millennia BC, to modern exhibits. The work is carried out by scientists at Cornell University, USA. The main results of the project:
- Absolute dendroscales of such species as oak, cedar, juniper, pine were made. Their period is estimated at 750 g BC.
- The construction of a floating Aegean dendroscale was completed with an accuracy of 2657-649 BC (for juniper).
- Also, a section of a tree in juniper helped to build a dendroscale floating for the period 2030-980 BC. The results were published in 2005.
- Known issues were identified on the โRoman gapโ and the EVA problem.
The achievements of American scientists are still considered controversial, since the probability of error in some cases is from 100 to 200 years.
Research in Finland
One of the suitable areas for exploration was northern Finland. In these places the line of the climatic border runs. Professor Jan Esper claims that sunken trunks have retained all information for hundreds of years. So, a small cut on a tree lying in a cold lake tells a lot. In the north of Finland there are many such lakes that store invaluable information. Dendrochronologists say they can uncover the secrets of climate for two thousand years. Using a special drill, laboratory workers manually extracted tree rings. They were then examined under a microscope using computer technology. Compiled dendrochronological graphs helped to recognize how the climate changed and even when volcanic eruptions occurred on the territory.
Climate change
According to the data, scientists were able to establish that on the planet every millennium the average temperature decreased by 0.3 degrees. This continued until the beginning of the twentieth century - the Industrial World Revolution. The development of scientific and technological progress has led to the fact that the amount of greenhouse gases on Earth has increased significantly. Dendrochronologists have not studied this period in detail.
At the time of Roman gladiators, the climate on the planet was much warmer. The "warm phase" can be called the Middle Ages. Then came the cooling, which continued every year until 1900. Our modern man, on the contrary, is now worried about global warming. As you can see, even a small cut of a tree branch can tell a lot. Unfortunately, with the onset of the greenhouse effect, with the conditions in which the atmosphere is polluted and the climate depends, in some way, on human activity, dendrochronology data can only indicate temperature fluctuations.