# How to count the age of a tree

## Tree Age Calculator - How Old Is a Tree?

Created by Mehjabin Abdurrazaque

Reviewed by Wojciech Sas, PhD candidate and Rijk de Wet

Last updated: Sep 28, 2022

• How to calculate the age of a tree?
• How to use tree age calculator?
• Tree growth factor chart — the smaller, the faster!
• FAQ

The tree age calculator guides you on how to calculate the age of a tree to understand its ecological and economical benefits, as you can learn at the tree value calculator. Our tool also tells you how much a tree grows in diameter or circumference in the given time so that you can design your yard suitably.

We also try to answer some interesting questions like:

• Do trees die of old age?
• How to tell how old a tree is by counting its rings?

And, don't forget to check our tree growth factor chart to find the fast-growing trees in your neighborhood!

### How to calculate the age of a tree?

The formula for calculating a tree's age is

age=gf⋅dbh\text{age} = \text{gf}\cdot \text{dbh}age=gf⋅dbh

Where:

• age\text{age}age — The tree's age in years;
• gf\text{gf}gf — The tree growth factor; and
• dbh\text{dbh}dbh — The diameter at breast height in inches.

1. Measure the circumference at breast height (cbh) of the tree trunk using a measuring tape at 4.5 feet (1.3 meters) above the ground.
2. Divide the circumference cbh by pi (≈3.14) to obtain its diameter at breast height (dbh\text{dbh}dbh).
3. Convert dbh\text{dbh}dbh to inches.
4. Multiply the diameter in inches with the tree species' growth factor.

Growth factor of a tree
To determine a tree species' growth factor, scientists first estimate the actual age of trees of that species by counting their growth rings. Then, they divide the trees' diameters at breast height (we met this quantity at our tree diameter calculator) with their actual ages to obtain the tree species' growth factor.

### How to use tree age calculator?

It's very simple: select the type of tree and input the tree's circumference or diameter. 😎✨

Suppose you want to know the age of your red maple with a circumference of 6 feet and 3 inches (= 2 feet in diameter). To determine your tree's age using our tool, you'd follow these steps:

1. Scroll down the tree species' drop-down list and select Red maple.
2. To calculate your tree's age from its circumference:
• Choose the unit for circumference at breast height (cbh\text{cbh}cbh) from the drop-down list beside its input box. For your red maple, the unit is feet/inches. Then enter the circumference of 6 feet and 3 inches (if you are not familiar with this way to express length, visit the feet and inches calculator).
• Enter the tree's circumference in the input box — 666 in the box to the left of ft\text{ft}ft and 333 in the box to the left of in\text{in}in.

Ta-da! The calculator shows your tree's diameter at breast height (dbh\text{dbh}dbh) is 61 cm61\ \text{cm}61 cm (you can convert the length to obtain the diameter in feet or feet and inches) and its age 107 years107\ \text{years}107 years! It's a centenarian!

If you want to tell the tree's age from its diameter:

• Choose the unit for diameter at breast height from the drop-down list beside its input box — feet ($$\text{ft}$$).
• Enter your tree's diameter in the input box — 222.

🙋 If you can't find your tree in the list, enter your tree's growth factor in the input box for Growth factor. Most tree species have growth factors of 3, 4, or 5.

Did you know that you can roughly estimate your tree's birthday using our date calculator! Just enter your tree's age in days and today's date in our tool, and you can obtain a date close to your tree's actual birthday.

### Tree growth factor chart — the smaller, the faster!

You can use our tree growth factor not only to calculate your tree's age but also to learn which trees grow faster than your tree. The rule is: The smaller the tree growth factor, the faster the tree grows.

While you are here, check out our tree spacing calculator. It will help you determine the correct distance for planting different types of trees.

The tree growth factor chart for many different species of tree.

Tree species

Growth factor

American beech

6

American elm

4

American sycamore

4

Austrian pine

4.5

Basswood

3

Black cherry

5

Black maple

5

Black walnut

4.5

Black willow

2

Box elder

3

3

Common horse chestnut

8

4.5

Cottonwood

2

Dogwood

7

Douglas fir

5

European beech

4

European white birch

5

Green ash

4

Honey locust

3

Ironwood

7

Kentucky coffee tree

3

Littleleaf linden

3

Northern red oak

4

Norway maple

4. 5

Norway spruce

5

Pin oak

3

Quaking aspen

2

Redbud

7

Red maple

4.5

Red pine (Norway pine)

5.5

River birch

3.5

Scarlet oak

4

Scotch pine

3.5

Shagbark hickory

7.5

Shingle oak

6

Shumard oak

3

Silver maple

3

Sugar maple

5.5

Sweetgum

4

Tulip tree

3

White ash

5

White fir

7. 5

White oak

5

White pine

5

Yellow buckeye

5

### FAQ

#### Do trees die of old age?

As a tree ages, its respiring tissue increases, but the photosynthetic area (leaf surface area) remains somewhat constant. Consequently, an older tree allocates more carbohydrates for life-sustaining respiration and less carbohydrate for root and stem elongation and repair, which initiates its senescence (physiological deterioration) phase. The tree becomes more vulnerable to diseases and other natural enemies and eventually becomes a snag.

#### How can I identify the fast-growing trees near me?

It's easier to find out which trees grow faster than others using the tree growth factor chart. The smaller the growth factor, the faster the tree grows!

#### How do I calculate an oak tree's age by diameter?

To determine an oak tree's age by diameter:

• Convert the diameter to inches.
• Multiply the diameter with the tree species' growth factor.
• The product is the tree's age in years!

For example, the age of your pin oak tree with a diameter of 3 ft at breast height (dbh) is 3 (the growth factor) times 39 (dbh in inches) = 117 years!

#### How do I count tree rings to estimate its age?

Each dark ring of the tree trunk represents a cycle of seasons, or one year. So, the total number of dark rings tells us the age of the tree in years. Count from the innermost dark ring to the outermost.

Mehjabin Abdurrazaque

Tree species

Growth factor

Circumference at breast height

Diameter at breast height

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## How to Tell How Old a Tree Is (Trick Works Every Time on All Tree Types)

Many people know the basic steps of how to tell how old a tree is using a simple trick… just count its rings. 1

It works every time. You can check the cross-section of the tree’s branch and start with the first dark circle. Count outward from this dark circle till you reach the outermost dark ring. The total dark rings give you the age of the tree. Please note that the bark doesn’t count as a ring.

But, this can be tricky unless you have a cross-section of the trunk, and that would require it being cut.

Fortunately, there’s a much better way to tell how old a tree is.

Use a tree age calculator that works using the tree species’ growth factor. You can do it yourself, or use this convenient tool!

### What Is the Trick to Tell the Age of All Trees?

The rings in a tree’s trunk are formed when cells divide and grow in layers during its life. The widths of these bands vary depending on the species and climate. By counting how many dark rings are visible on a tree trunk, you can calculate how old it is.7

However, if you use the calculator above, you can get a very close estimate to a tree’s age, without needing a cross section.

Here are some tips for using it:

• When measuring the circumference of the truck, a fabric tape measure works well, but if you don’t have one, you can use any length of string. Just mark the string, lay it out flat, and then measure it using a regular tape measure or yard stick.
• When making the circumference measurement, make sure to place the string around the trunk at about 4’6″ from the ground… this is about the height of a standard counter top, plus about a foot.

In general, if you see more than seven (or eight) annual growth rings per centimeter, your tree is quite old; if you see fewer than five or six per centimeter, it’s probably younger than that; and if there are none at all, then you have an ancient specimen whose age may be impossible to determine with confidence.

### How To Tell Age of Tree Without Cutting it Down?

Knowing a tree’s age is an essential aspect of tree management. It determines how fast a tree grows, how long it will stay alive, and whether or not it needs to be cut down. There are many methods to determine the age of a tree without cutting into it, but they all have their drawbacks. Some of these methods include:

• Stem diameter2 (the larger the diameter, the older the tree)
• Bark thickness (the thicker the bark, the older the tree)
• Millimeter-scale growth rings in the trunk (the more rings present in a section of the trunk, the older that section is)

### How To Count Tree Rings for Age?

Tree rings are natural markings on the tree trunk that indicate how old it is. A tree’s age can be determined by counting the number of rings, which is how scientists date trees. The number of rings on a tree varies by species and location, so it’s important to know what kind of trees you’re working with when estimating their age.

The amount of information found in these rings depends on many factors, including climate and soil conditions. For example, the temperature will affect how fast your tree grows if you live in a cold climate. This means your tree will have fewer rings if it lives in a cold climate than if it lives in a warm one.

Related Reading: How many trees does it take to build a house?

Counting tree rings can be tricky because there are so many variables involved! If you don’t have experience counting tree rings, it’s best to find someone who does this regularly or hire an expert to help you!

### How To Use Mitchell’s Rule Tree Age Calculator

Mitchell’s rule helps calculate a tree’s age by assuming that a tree’s girth expands by about 2.5 cm each year.

This means you can measure the girth of a tree and divide it by 2.5 to get the age. But, it’s not always the most accurate method.

Related Reading: How many Christmas trees per acre can you plant?

Instead, by using a tree’s specific growth factor, you can approximate its age and still enjoy the stunning beauty of the living tree.

### Tree Diameter Age Estimation Chart

One of the most dependable ways to estimate the age of a tree is by multiplying its diameter by its growth factor. Below are the growth factors for some common tree species.

 Tree Species Growth Factor Red Maple 4.5 Silver Maple 3.0 Sugar Maple 5.5 River Birch 3.5 White Birch 5.0 Shagbark Hickory 7.5 Green Ash 4.0 Black Walnut 4.5 Black Cherry 5.0 White Oak 5.0 Red Oak 4.0 Pin Oak 3.0 Linden 3.0 American Elm 4.0 Ironwood 7.0 Cottonwood 2.0 Dogwood 7.0 Redbud 7.0 White Ash 5. 0 Aspen spp 2.0 American Beech 6.0 European Beech 4.0 Basswood 3.0 European White Birch 5.0 River Birch 3.5 Paper Birch (aka White) 5.0 Yellow Buckeye 5.0 Kentucky Coffeetree 3.0 Douglas Fir 5.0 White Fir 7.5 Common Horsechestnut 8.0 Littleleaf Linden 3.0 Black Maple 5.0 Norway Maple 4.5 Northern Red Oak 4.0 Scarlet Oak 4.0 Shingle Oak 6.0 Shumard Oak 3.0 Bradford Pear 3.0 Austrian Pine 4.5 Red Pine 5.5 Scotch Pine 3.5 White Pine 5. 0 Tulip Poplar (Tulip Tree) 3.0 Colorado Blue Spruce 4.5 Norway Spruce 5.0 Sweetgum 4.0 American Sycamore 4.0

### How Old Is a Tree With 3.0 Rings?

If you want to know how old a tree is, and have a number like 3.0, it’s the growth factor. A growth factor is a rate at which a tree grows.

Pin oak, Silver maple, and linden have a 3.0 growth factor. You should find the diameter of a tree and then multiply it by the growth factor (3.0). For example, if the diameter of a silver maple is 16 inches, its age is 48 years.

Related Reading: How many pieces of paper in a tree?

### How To Find the Maximum Age of Tree

There is no correct answer to this. The maximum age depends on various things such as the weather, soil, and other factors that may affect its age. If you are looking for the maximum age of a tree, you can use an online calculator, which will give you a range of ages for your tree.

The best way to find out how old a tree is is to look at it yourself. You can use a ruler or tape measure and see if there are any evident signs that your tree has reached its maximum age. You should also remember that trees grow at different rates depending on their species, climate, soil type, and other factors, so it is impossible to say how old your tree will grow without researching first!

### How To Figure Pine Tree Age by Diameter

Pine trees are often used for landscaping purposes, and their age can be determined3 by measuring their diameter and multiplying it by the growth factor.

Start by taking hold of the tree’s trunk and measuring the circumference. For example, if the circumference is 20 inches, the diameter will be 20 divided by 3.14. This will give you 6.36.

Related Reading: How many trees are planted each year?

The growth factor of a pine tree is 5.0. So the pine tree’s age in this example would be approximately 31. 8 years.

### International Society of Arboriculture Tree Growth Factor

The International Society of Arboriculture uses the diameter of a tree to figure out its age, which is then used to determine whether or not a tree is healthy.

The diameter is measured by figuring out the circumference of a tree first. Use a tape measure to measure the tree’s circumference and divide the number by 3.14. Once you have the diameter, multiply it with the growth factor to get the tree’s age.

### How To Tell How Old a Tree is by Rings

A tree’s lifespan is determined by how often it produces and sheds its leaves and how much water it receives. A tree’s age can be determined based on its size, the number of rings in its trunk and branches, and whether or not the tree is still alive and growing.

The number of rings that your favorite tree has can be used to determine its exact age. Your local park department may also have an arborist who can tell you how old your favorite tree is based on its appearance and size.

Related Reading: How many trees are in the world?

There are several types of trees with varying methods for determining their ages. The deciduous (or “leaf”) tree is the most common type of tree; these include maples, elms, oaks, and birches. Other types include conifers (including pine trees) and evergreens (spruce trees, cypresses, and cedars).

Some trees have unique characteristics that allow for easy determination of their ages; for example, maples have visible rings which can be counted as part of determining their age.

### How To Tell How Old a Pine Tree Is

It’s easy to determine the age of a pine tree. You first need to find the diameter of the tree. You can do this by measuring the circumference and dividing it by 3.14. Once you have the diameter, you multiply it by the growth rate.

The growth rate for a pine tree is 5.0. This calculation helps you determine the age of any pine tree.

### How To Tell How Old a Palm Tree Is

Usually, the best way to tell the age of a tree4 is by looking at the trunk’s rings. However, palm trees do not have very thick trunks, so this method would be complicated.

You can check a palm tree’s age by checking if it survived radiocarbon dating. This is a method that checks the chemicals and assesses the age of the tree. Since this method is scientific, you would need an expert to help determine this.

This method, however, does not account for ailments and habitat. These factors do hinder growth.

### How To Tell How Old a Redwood Tree Is?

To determine how old your tree is, simply use the ring method. The more the number of rings, the older the tree is. Most redwood trees live long, so this method may be time-consuming and frustrating.

Redwoods also have scars from diseases that affect their growth rate, but these scars do not always appear on the outside of their trunks.

If you see a dark patch on a redwood’s outer bark or trunk, this means there was a large-scale infestation of fungal root rot that caused damage to some parts of the tree’s root system. This is also a factor you should consider when calculating its age.

### What Do Tree Rings Mean?

Tree rings are a form of tree growth that can indicate the age of a tree. It is essential to know when an individual tree was planted and how old it is. This can be used to determine whether or not a species is growing at the rate it should be.

To understand what tree ring samples mean, you need to understand what they are and why they’re essential. Tree rings are made up of a series of layers that form around a tree trunk after it has been cut down or pruned, which makes them easy to identify.

The different layers form in different parts of the tree depending on what caused them to grow in that area. For example, if an insect attacked the bark during growth, that part of the ring will show up as more brittle than other parts due to lackluster growth during that period.

### Are Thick Tree Rings the Same as Smaller Rings?

The answer is yes, but not in the way you might think. Thick tree rings are a marker of a tree that grew in more favorable conditions. The thicker the ring, the more years and growth cycles it took for the tree to reach its full height.

This means that it could bloom and produce fruits earlier than other trees of its species.

Related Reading: How much carbon does a tree capture?

Smaller rings mean a tree did not reach its full height because it lived during a period when weather conditions were less favorable for growth. In other words, some trees do not grow larger than others because they couldn’t thrive under ideal conditions.

### How Are Black Tree Rings Formed?

Black tree rings are formed when a tree grows during late summer and fall. This is because the leaves on a tree are still alive at this time and produce sugars. The sugars are then transported to the leaves through photosynthesis, which converts them into starch.

When the leaves wither back in the spring and summer, it’s only then that the sugars begin to be depleted. The trees begin to store energy by building up their wood matter, especially if there is not enough food available for them during their winter months.

They also begin to lose their leaves early in the spring because they do not have enough energy from photosynthesis to maintain them throughout the warmer season.

The trees’ reserves of energy are depleted as they cannot produce enough starch during these months while they build up more wood structures in preparation for winter.

### How To Care for Older Trees?

Trees are an essential part of the ecosystem and can be a great addition to the landscape. However, there comes a time when you need to learn how to care for your trees and keep them healthy and happy. If you have older trees in your yard, you will want to know how to care for them so they can live a long healthy life.

The first thing you should do is make sure that you are watering your trees properly. If they are not getting enough water, they might not be able to grow to their full potential. You should also ensure that the soil around your tree is good and has plenty of nutrients so the roots can get what they need from there.

You should also ensure that all dead branches on your tree are cut off before winter comes because this will help protect them from freezing during cold weather. While it may seem easy at first glance, it requires some work upfront so that you can enjoy these beautiful trees for years to come!

Trees provide the planet with a much needed, and abundant source of carbon capture technology. Older trees especially need to be protected using carbon offset tree planting strategies and many of the best carbon offset programs do just that. These older forests work to reduce the overall eco footprint of the planet, and can be strengthened with new growth while protecting the old growth.

### Are Older Trees More Susceptible to Diseases?

Trees over 30 years old are more susceptible to diseases5 because they have already had many years to develop their immune systems. If you have an older tree, it’s essential to ensure that you take care of it properly to prevent disease.

This means regularly watering the tree, keeping the soil moist, and not allowing the roots to dry. Ensure your tree gets enough sunlight by placing it where it gets plenty of natural light throughout the day. If you have a large tree, consider planting it near a fence or other structure so that it can get shade during hot summer days.

### Can You Tell the Age of a Tree by Looking at its Leaves?

If you are looking for information about trees and how they grow, then yes, you can! Trees have leaves because they need them to photosynthesize. This means that they need sunlight to survive. When a tree is young, its leaves will be green and healthy. As it grows older, the leaves will begin to change color and become more mature.

If you want to find out how old a tree is, use the ring counting method. This will give you an idea of how long it has been since it was planted.

You can also use this method when you’re trying to determine if your tree is healthy or not. If there are cracks in the bark or pieces missing, this could mean that the tree needs some TLC before it can live another day!

It’s essential to know a tree’s age so you can care for it adequately. It’s also important to know the specific kind of tree you have and what its health needs are.

For example, if your tree has brown spots on its leaves and looks unhealthy, you might suspect a fungal infection. If you suspect this, it is recommended that you call a professional to come out and assess your tree.

The best way to care for your tree is by keeping it healthy, which means being able to monitor the health of its roots and trunk and applying natural pest fighters and fungal treatments when required.

As you know, a tree’s lifespan is directly linked to how well it’s cared for. A tree expert will be able to recognize a variety of indicators that provide clues to its age. So, if you want to maximize your enjoyment of the beautiful trees around you, it’s worth investigating if you could do anything better for them. Knowing how to tell how old a tree is can help you inspire others with a love and respect for these vital parts of nature.

## How scientists determine the age of things

### Method One: Dendrochronology

Tree growth rings are a pattern that climate change creates. This pattern remains on old buildings and other wooden things and betrays their age.

How it works

Any schoolchild knows that the age of a tree can be determined by the number of growth rings on the cut. They appear due to the fact that in summer the tree grows quickly, and in winter cold growth slows down. Therefore, on the cut one can see the alternation of wide light rings of the warm season and narrow dark ones of the cold season.

Tree stump rings tell more than just the age of the felled tree. They judge climate changes: one year could be dry - and the tree grew more slowly, and the second, on the contrary, turned out to be rainy, and the tree grew great. Therefore, trees growing in the same region at the same time develop a similar pattern of growth rings. Scientists make archives of these patterns, then compare them with the pattern of wooden archaeological finds and determine the age of the finds. Wood clocks cover a period of more than 8000 years, and their accuracy reaches 1 year: after all, a tree adds only one ring per year.

Application example

In Veliky Novgorod, dendrochronology was used to date ancient pavements. A long time ago, Novgorod streets were narrow, three to four meters wide, but they were paved with glory: three pillars of logs with a diameter of 18-20 cm were laid along the street, and thicker logs with a diameter of 25-30 cm were laid on top. Approximately once every 20 Over the years, this impressive wooden structure has been renovated, and new logs were laid on top of the old logs. Such are the puff pies of wooden pavements: in some places, as many as 28 tiers have been preserved! Dendrochronologists had a place to roam.

Dinosaurochronology

Dinosaur bones also have growth rings (as well as amphibians, reptiles, and some mammals). Light rings are wide and looser layers of bone tissue, which are laid down during periods of active growth: in spring and summer. And in winter, thin and dense layers formed. By peering into the rings of a dinosaur, scientists can understand how it grew and developed over its lifetime.

### Second method: geochronological record

Different fossil animals and plants are characteristic of different geological periods. Almost like in the Chinese calendar: only instead of the year era - trilobites, unicellular fossils, etc. If an archaeologist or geologist has found such a characteristic fossil, then you can determine the approximate age of the reservoir.

How it works

Here lies a layer of rocks in front of the archaeologist. In this bed, he found some kind of fossil and is trying to figure out how old the fossil is. Guiding fossils will help him establish the geological era - plants and animals characteristic of a certain geological period, but not found either earlier or later.

To qualify as a leading fossil, a fossil must meet several difficult requirements: it must be easily recognizable, occur frequently in sediments, have a wide geographic distribution, and have a narrow time frame. If an archaeologist or geologist saw acritarchs * in the excavated layer, then he was in the Upper Precambrian. And if you stumble upon the shell of extinct arthropod trilobites, then the geochronological clock has struck the Cambrian**.

*Acritarchs are microscopic fossils of unicellular or seemingly unicellular organisms.

**Cambrian is a geological period that began 540 million years ago. We know little about the inhabitants of the Precambrian, and the Cambrian is characterized by the appearance of a mass of diverse multicellular creatures - the Cambrian explosion.

Application example

In 2014, members of the Pavlodar Geographical Society decided to go on a small expedition to the Shiderty River. It would seem that an ordinary river in the middle of the steppe, on the bank of limestone, some pebbles. But it was worth taking a closer look at the pebbles: some of them turned out to be fossils of ancient brachiopod molluscs. Yes, yes, in the steppe, far from the sea and the ocean, scientists have found the remains of marine animals. These fossils seem to whisper to researchers that hundreds of millions of years ago, in the far, far Devonian, the ancient Tethys ocean raged here.

Time passes - radioactive isotopes decay. If you know what fraction of the isotope has decayed, you know how much time has passed.

How it works

The guide fossils described in the previous chapter are a way to measure the approximate age of a find. To determine it more precisely, scientists use radioisotope dating. If an object contains a radioactive isotope*, then, based on its half-life and how much of the isotope has decayed, you can calculate the age of the object.

*Isotopes are varieties of the same chemical element with different numbers of neutrons in the nucleus. There are stable isotopes, and there are decaying over time - radioactive.

The most famous variation of this method is radiocarbon dating. Living organisms, along with food, absorb both ordinary carbon 12C and radioactive 14C. But when a plant or animal dies, it stops exchanging radioactive carbon with the environment. Remaining in the body, it gradually disintegrates, and its residual proportion becomes an indicator of age.

The limit of radiocarbon dating is 55,000-60,000 years. But there are other isotopes that allow you to look much further into the past. They are also used to measure age. For example, a very convenient mineral is zircon, it is used for uranium-lead dating of rocks. Zircon contains uranium isotopes, which then decay into lead isotopes. The starting point - analogous to the moment of death of an animal for the radiocarbon method - is the crystallization of zircon during lava cooling. There are other methods: potassium-argon, argon-argon, lead-lead.

Application example

In 1988, a report on radiocarbon dating of the famous Christian holy shroud, the Shroud of Turin, made a lot of noise. The traditional version says that this canvas contains traces of the blood of the crucified Christ, that is, it refers to the 1st century AD. But radiocarbon analysis conducted in three laboratories (Oxford University, Arizona State University and the Swiss Institute of Technology) showed that the shroud is much younger - about 1200-1300 years old. Around the same time, in 1353, the first mention of the shrine was recorded.

### Fourth method: spectral analysis and gyrochronology

How to understand how old a star is? After all, it is impossible to reach out to it and take a piece for analysis and dating. So you have to watch how it glows and spins.

How it works

Stars age very unevenly: they do not change for 90% of their lives, and then they suddenly begin to transform dramatically. You can imagine it this way: a person reached the age of 3-4 years, then did not change for 80 years, and then turned gray in a year, hunched over and died. Astronomers are in a difficult position: it is very difficult to determine how old a star is.

Fortunately, much can be seen by looking closely at her light. If you expand the spectrum of the Sun, you get a rainbow with thin, thin black lines. These are absorption lines that correspond to different chemical elements. From the spectral absorption lines, one can judge the composition of the star. What does age have to do with it, you ask? The fact is that in the process of a thermonuclear reaction * the hydrogen in the star burns out, and the helium content grows. This means that the older the star, the more helium and less hydrogen in it, and you can see this from the absorption lines in the spectrum.

*We remind you that a star is a giant thermonuclear reactor in which helium nuclei are synthesized from hydrogen nuclei (that is, from protons).

In addition, the age of a star reveals its rotation period*. A young star spins at a certain speed, which steadily decreases as it grows older. One problem - it is difficult to see this rotation, very sensitive telescopes are needed. Astronomers use sunspots as a guide. But working with old stars is problematic because they have fewer and fewer spots. The method of determining the age of stars by rotation is called gyrochronology.

*Stars, like planets, rotate around their own axis. The sun, for example, makes one revolution in 30 days.

Application example

The Kepler space telescope, the same one that has already found thousands of exoplanets, helps scientists observe the rotation of stars. To calibrate the gyrochronology method, in 2011, scientists at the Harvard-Smithsonian Center for Astrophysics tracked the 1-billion-year-old star cluster NGC 6811. It turned out that the stars of this cluster rotate around their axis about once every 10 days, as predicted by the method. Scientists decided to track the stars of the older cluster - NGC 6819, they are about 2.5 billion years old. And again, the speed of their rotation coincided with theoretical calculations - the method worked. But the arrows of gyrochronology still have to be tweaked, making adjustments for different groups of stars. Sometimes they don't spin the way the calculations predict. As soon as the magnetic field weakens, the star begins to "younger" - to spin faster.

### Method Five: Paleomagnetism

Ceramics and other ferrous materials are a broken compass: they show the Earth's magnetic field of the past. Therefore, the magnetization of antiquities can indicate their age.

How it works

Archaeologists often come across ceramics: earthenware pots broken a thousand years ago, fragments of antique wine jugs, plates that once long ago gathered dust in our ancestors’ cupboards, bricks... It turns out that science is capable of to tell when the excavated brick was burned in a furnace or when porridge was last cooked in an ancient pot. The point is paleomagnetism: at high temperatures, iron-containing materials like clay become magnetized, and when they cool down, they seem to “remember” the direction and intensity of the Earth’s magnetic field at a given moment (they are constantly changing, after all). The information that the pot or kiln retained at the time of firing can be analyzed and correlated with the chronological scales of the change in the magnetic field. So scientists find out the age of ancient ceramics with an error of only 10 years.

Application example

In the Trans-Baikal Territory there is a hill strewn with fragments of stones and tiles; some of them show green icing. In some places, the bases of columns peep out of the grass. This is the Kondui settlement. 600 years ago, here, in the valley of the Kondui and Barun rivers, stood the palace of the Genghisides, the heirs of the great Mongol Khan. Gold-plated discs of dragons glittered on the roof of bright green tiles, and monsters scowled from the walls. During the excavations of the Kondui Palace, archaeologists came across an abundance of building ceramics: several types of bricks, floor slabs, and tiles. So, somewhere nearby there should have been large kilns for firing. Paleomagnetism helped archaeologists find these furnaces. Ancient structures that were once heated to high temperatures remembered the Earth's magnetic field of the past and fonils, creating magnetic anomalies. Scientists identified them using a quantum magnetometer, found furnaces and divided them according to their functions: here they made bricks, and here they made tiles. So we learned a little more about the medieval palace, from which only tiles and a legend remained*.

*Once upon a time rich and powerful Tumur Khan lived in Mongolia. He had a son, Contoy. Traveling around the country, Contoy fell in love with the beautiful Baljit and married her without the permission of his father. Fearing his father's wrath, Kontoy settled near the river Kondui, became a khan and built a palace. But the father did not forgive his son and sent troops against him. The beautiful Baljit was killed, Kontoy was captured, and the palace was destroyed.

### Sixth method: epigenetic clock

Cells are traitors worse than wrinkles. In their DNA (and not only in DNA) they store age markers that cannot be hidden.

How it works

Scientists use DNA to determine cell age. The fact is that as the cell determines its profession - whether it will be a neuron or a vessel cell - it winds the genes it does not need into balls and fixes them with something like molecular adhesive tape - methylation. The sections of DNA, on which the methyl group has been hung, become sticky and stick together with each other. Generally, the older a cell is, the more coiled DNA it has.

Knowing that the methylation profile changes with age, Steve Horvath, professor of human genetics and biostatistics at UCLA, analyzed human DNA methylation data for four years. And in 2013, he received an epigenetic clock that makes it possible to determine a person’s age by the methylation pattern of 353 DNA regions with a very small error. This indicator is many times more accurate than many other signs of aging, for example, the length of the DNA end section - telomere.

You can also see how the cage cleans up internal debris. One of the "cleaners" used by the cell is the digestive enzyme beta-galactosidase. It gets bigger with age.

The cell is gradually, division by division shortened. After about 50 divisions, telomeres end, the cell loses the ability to divide and becomes decrepit.

Application example

Horvath's epigenetic clock was first used a few years ago by European forensic scientists. The fact is that when a refugee without documents arrives in the country, his age is estimated by eye or from his own words. It is beneficial for a refugee to reduce his age, because minors have more rights and privileges. For example, they may summon adult relatives to the country or receive a lighter sentence for a crime. For example, in 2018, a young Afghan refugee filed a lawsuit against the police in the German city of Hildesheim demanding to recognize that, as a minor, he can count on concessions. The police responded by turning to age-determining methods based on methylation patterns. The actions of the authorities were then criticized because of the immaturity of the technology. But will the "Horvat's watch" ever mature?

Stress instantly made her an old woman!

Unlike a person, a cell can become decrepit at any moment - no matter how old it really is. To age, a cell only needs to be exposed to severe stress, such as exposure to toxic substances. After such a shock, she refuses to work normally and benefit the body. Scientifically decrepit cells are called senescent.

### Seventh method: measuring the temperature of a corpse

We saved a gloomy example for the brave in spirit for the finale. It's not really about age - it's more about the fact that the medical examiner must carefully examine, sniff, feel the corpse and take its temperature in order to determine the approximate time of death.

How it works

There is a common plot in TV series about forensic science: the medical examiner moves his hands over the body, drops something into a test tube, looks through a microscope and names the exact time of death. In reality, everything is not so sterile-contactless. Rough and approximate indicators of the time of death are rigor mortis and cadaveric spots. Rigor occurs because muscle cells need energy to relax, and a dead body does not have it. Stopped blood circulation is to blame for the spots: the heart and vascular tone no longer drive the blood, therefore, under the influence of gravity, it moves and accumulates on the underside of the body.

The medical examiner can examine muscle irritability in a variety of ways. But most often he uses a simple and accurate method - temperature measurement. While the body has not yet cooled down to the ambient temperature, cooling occurs according to a certain schedule. The medical examiner measures the temperature, enters correction factors into the formula depending on body weight and cooling conditions (ambient temperature, clothing, humidity, and so on) and, taking into account other signs, sets the approximate time of death. Only the temperature must be measured very accurately: the usual method of "thermometer under the arm" is not suitable, nor is an infrared thermometer. The temperature has to be measured rectally.

Application example

Researchers in the Netherlands have recently suggested determining the time of death by skin temperature rather than rectal temperature. This method allows you to set the moment of death with an accuracy of 38 minutes, and not with an error of several hours, like earlier methods. Scientists came up with a mathematical model of cooling: they took the shape of the head as an ellipsoid, the limbs as cones, and the torso and neck as cylinders. Cooling time was then modeled for each item, taking into account body weight, thermal conductivity of fat, lean tissue, and cotton garments. They also examined the bodies of donors who bequeathed themselves to science. The method worked: the predictions that the model gave out coincided with the temperature that was observed in reality.

Prehistory of the scientific measurement of time

6000 BC e. - Sumerians in Mesopotamia use the concepts of "year", "month" and "zodiac".

At this time, the Sumerian zodiac is 36 constellations in which the Moon appears, and not the Sun, because the first calendar is lunar. Later, the Sumerians will come up with a "week".

5000 BC e. - the first annual calendar circles known to science.

Even then, on the territory of modern Germany, the beginning of the new year, like here, fell on the winter solstice.

3300 BC e. - the first sundial.

Discovered in 2013 in the Valley of the Kings in Egypt.

3000 BC e. The ancient Egyptians use the solar calendar.

A year consists of 365 days and is divided into 12 months of 30 days. The remaining five days are added at the end of the year.

2500-1300 BC e. - Water clocks are used in Persia, Mesopotamia, Egypt and China.

Water clock is a device for measuring time intervals in the form of a cylindrical vessel with a jet of water flowing out.

45 BC e. - Julius Caesar introduces the calendar developed by Alexandrian astronomers, named after him Julian. The year in it begins on January 1 - the traditional date of entry into office of elected consuls.

By the way, the word "calendar" comes from the Latin calendarium - debt book. In Rome, debtors paid interest to creditors on the first days of the month.

725 - The first mechanical watch is created in China.

Arabs soon borrowed them.

XIV c. - in some European cities, mechanical clocks appear on the towers, at first without a pendulum and a minute hand.

Dante describes such clocks in the Divine Comedy (at the very beginning of the 14th century).

1504-1508 - Invented the first pocket watch.

According to legend, they were created by craftsman Peter Henlein from Nuremberg during his stay in a poor shelter.

1656 - Dutch scientist Christian Huygens creates the first pendulum clock.

The pendulum clock remained the most accurate instrument for measuring time for 300 years.

## How to determine the age of an oak tree

How to determine the age of an oak tree, a question that sooner or later gardeners or just passers-by face when looking at a huge and powerful representative of this tree species. And since oaks are long-lived and have a fairly strong trunk and a luxurious crown, it’s not so easy to answer the question about age. For all the time of the existence of mankind, there are only a few ways to find out this information. Let's consider them in more detail.

Since childhood, we were told that the age of any tree can be determined by counting the annual rings on the cut of the trunk. Yes, this is true, but the method, firstly, is too radical, because it is unlikely that someone will cut down an oak tree just to find out its age. There are other, less radical methods that can provide information of interest to us. These include:

• whorls count;
• stem diameter measurement;
• Pressler drill application.

But none of the methods described above will help to determine the age of a tree with an accuracy of 99%, why we will consider this further.

Therefore, if the question is quite fundamental, then in addition to the methods described, it is necessary to resort to searching for information about the oak you are interested in. It is collected in several ways. The first is a survey. It is necessary to interview local residents, for sure someone has information about when the tree was planted or maybe knows for sure that it grew in this place when his grandmother was a child (such information gives certain ideas about age). The second way is to study documents and photographs. These can be newspaper archives, home photo albums, and if the tree grows in a park area, then you can try to find information from the city authorities. After all, most likely the alleys and parks were planted during subbotniks or were timed to coincide with some memorable events. It happens that the tree of interest grows on the territory of someone's former estate or church, then it is worth looking for information about the owners of the estate or studying historical data about the church and talking with the priest. Sometimes the search for the necessary information allows you to get the most reliable data, and besides, to learn a lot of new things, and not only about the tree.

But if it was not possible to determine the age of the oak by information, then it is necessary to proceed with biological.

And so, counting whorls. What it is. Simply put, it is necessary to count the number of tiers of tree branches that are located around the trunk. Every year the tree forms a new ring of branches. Having counted the whorls, it is necessary to add the number three to their number, since the oak only in the third year begins to form branches that form the annual circle. The added numbers are the age of the tree. But, since the oak belongs to the centenarians, and today individual specimens are known that are already more than a thousand years old, this method of determining the age of it is suitable only for young trees. This is due to the fact that after thirty years of life, the lower branches of oaks begin to die off and fall off, and its size can reach fifty meters in height, so it is almost impossible to correctly calculate whorls.

The next way to determine the age of an oak tree is to measure the diameter of its trunk. This will require a special device - a forest measuring fork, but you can also use a regular tailor centimeter for measurement. Measurements are taken at a distance of one meter thirty centimeters from the ground. Having measured the circumference of a tree, simple mathematical calculations determine the diameter through the circumference and the number pi. Next, you need to know the data on the average annual growth. Oak grows on average by forty-four millimeters. To calculate the age, the diameter is divided by a factor of 44. This is how we find out how old the tree is. But it should be noted that melon calculations have a mathematical error of five to fifteen percent. Since it is impossible to give exact figures on annual growth. These natural processes depend on the environment and conditions in which the tree grows.

The indicated methods for determining the age of a tree are quite loyal and allow you to determine the age without cutting down the trunk.

Less loyal, but still not so cardinal, is the use of a Pressler drill. With it, you can take a sample of wood from the bark to the core. Rings are counted on the obtained sample. Now a few words and technique. The drill must be suitable in size, its length is seventy-five percent of the diameter of the tree.