How the age of the Earth was Calculated?

What is the age of the earth? Nowadays we know the answer to this question but back in the decade of the 60s and 70s, it was the most sensational question.

Today we know the age of the Earth and that is around 4.5 billion years. But how was it calculated? How someone found the age of the earth?

In today’s article, I am gonna tell you how the earth’s true age was calculated? And what were the challenges faced by the man who calculated it? And the key figures in the research of the age of the Earth.

Archbishop James Usher’s Theory

In the year of 1650, Archbishop James Usher of Ireland made a calculation on the age of the earth. This calculation has somehow seemed very satisfactory and the problem was settled for time being.

Like everyone else of his time in the world, he accepted the biblical theory of the creation of humanity. But as we know, the bible does not give the exact year of the creation.

So, Ussher searched for an event in the Old Testament that corresponded to a known historical date. He found that in the second book of the kings and that was the death of Babylonian King Nebuchadnezzar in 562 B.C.

Ussher added up the generations of the Prophets and the Patriarchs. He found the time between Adam and Nebuchadnezzar and discovered the age of the earth.

The world began on 22nd October in the year 4004 B.C. at 6:00 PM and that was a Saturday.

This chronology of Archbishop Ussher was taken as a gospel in the western world. This theory was believed until someone found the other way of finding the true age of the earth. That method was calculating the sedimentary layers in the grand canyon rocks.

Layered Sedimentary Rocks of Grand Canyon

Rocks in the Grand Canyon, USA, are made of sediments, deposited as fine grains in the time when this part of the world was a sea.

The sediments were compressed into the rock under the weight of succeeding layers. This way the oldest ones are at the bottom. Each layer had taken some time to be deposited.

Do you want to calculate the age of the earth? Just calculate how long it took to deposit each layer. And then instead of counting the “Begats” like James Ussher, add up all the layers.

Easy, Isn’t it? But there is a problem. We know from observing this process because it still happens today in the ocean and lakes around the world. The sediments can be laid down at widely different rates.

It usually happens very slowly, say a foot of sediments take around 1000 years. But in case of a rare catastrophic flood, it can happen much faster, as much as a foot in just a few days.

Many geologists tried this method to calculate the age of the earth. They used the Grand Canyon and other sedimentary sequences around the planet.

But their responses ranged too widely to be of much use, it was anywhere between 3 million years and 15 billion.

There was one more problem with this method and that is even the deepest layer of the rock is not the oldest one. Why? Because not even rocks could survive the earth’s violent infancy.

An Asteroid drift in the Space

Moving to space where everything started. Even our earth and the other planets of the solar system. Million years ago, an asteroid from the asteroid belt located in between the orbit of the Jupiter and Mars got collided with another huge asteroid.

This collision resulted in the diversion of the path of the first asteroid. Due to this diversion, the asteroid moved towards the earth. It clashes the earth around 50,000 years ago at a place called Arizona today.

The Iron fragment of that asteroid has survived intact. If we somehow find out long ago that iron was forged, we would know the age of the solar system. Including the earth.

But how could we know that? Take a rock any kind of rock. Some atom in that rock could be radioactive which means they spontaneously disintegrate and become other element.

Nuclear Transmutation

A Uranium atom first becomes a thorium atom. On average, this process takes a billion of years. The thorium is much more unstable. In less than a month it turns into an atom of Protactinium.

A minute later, the Protactinium atom becomes something else. The atom undergoes 10 more nuclear transmutations until it reaches the last stop of the decay chain. A stable atom of lead and the lead will remain for eternity.

In the 20th century, there was a huge effort, lasting decades, to measure the time it takes for each radioactive element to transmute into the other element.

Physicists discovered that the atoms of each unstable element decay at a constant rate.

Keeping this in mind, what will be the best way to find the true age of the earth than with the Uranium atom? If you know what fraction of Uranium in a rock transmuted into the atom of lead. You can calculate how much time had passed since the rock was created.

But there is a problem. The rocks in the earth that were present when it was formed are no more. They’ve all been crushed, melted, remade.

Still there is a way to calculate the amount of lead that was present from the beginning. It’s a gift from the heaven. Meteorites.

There is a fragment of the asteroid that made the giant crater in Arizona. The amount of lead in that meteorite is exactly the same as when the earth was formed.

Since you know the constant decay rate of uranium, that should give you the age of the meteorite which was made at the same time when the earth was made.

All you have to is calculate the amount of lead in the meteorite. Easy, is’t it?

Clair Patterson & Harrison Brown’s Coalition

A scientist named Harrison Brown, at the University of Chicago, understood this for the first time in 1947. He chose a young graduate student, Clair Patterson to do the work.

Clair Patterson was a son of a letter carrier from Iowa was rebellious by nature and not very good in school. But he was a natural born scientist.

Mr. Brown introduced tiny particles called Zircons to Mr. Patterson. Harrison Brown told Patterson to find out the amount of lead in the zircon crystals. As he already has detected the age of the meteorite but they had confirmed it by the amount of lead in the zircon crystals.

Clair Patterson started his work on calculating the amount of lead in the zircon crystals. While Patterson was calculating the amount of lead, there was one more graduate student name George Tilton, whose work was to calculate the amount of uranium in the same crystal.

Tilton measured it six times and his results were always the same. But Patterson’s result on the same grain was very inconsistent which made no sense.

He taught, may the amount of lead in the lab was messing up with his results. So, he did everything to cleansed the lab but there still a 100 times high amount of lead in the results. He was working on it for the last two years but there no accurate or constant result.

The Ultra Clean Room

Then he decided to recontaminate the lead and purified all his apparatus with acid to reduce the lead in the lab. But this still not resolved the problem.

He was at this work for the next six years more and in this process, he made an ultra-clear lab room for his experiment. And he was ready to calculate the amount of lead in the fragment of the meteorite.

He brought his meteorite specimen to the Argonne National Laboratory where the world’s most accurate mass spectrometer had just became operational.

A mass spectrometer uses a magnet to separate elements contained in a sample. So, the amount of each element can be quantified. This would provide the last missing piece of the puzzle of the true age of the earth.

From the data received from the mass spectrometer and the calculation based on it, Patterson found the true age of the earth. The true age of the earth was 4.5 billion years.

You should read this too : Amazing Facts of the Universe

Closing Remark

From the descriptions above, we come to know that the earth is around 4.5 billion years of age. And this was not easy to be calculated.

As we all know that every experiment and theory has a negative side along with its positive one. The calculation of the age of the earth was not remained untouched of negativity.

This experiment arose a mental trauma to Mr. Patterson. Now by the interaction of so much lead and researching on it Mr. Patterson found that the lead very harmful for us.

That time, the gasoline were mixed with lead and as we know lead do not change to another element. It remain for eternity in gasoline and in the atmosphere due to the burning of the gasoline.

Mr. Patterson did everything he could do to stop this. We would discus more about this event some other time in some other fresh article. Till then have a good life.

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