Hello, in the first video of this series I talked about how the radioactive decay and
half life of an element works.
And it is on the basis of these concepts that we can do radiometric dating.
If we think about the U238 example, we know that it has a series of decay.
We know that it decays to Th234 which then decays to protactinium 234 and this is followed
by a number of elements until it reaches the lead 206 which is a stable element. you have
minerals that contain uranium over time that uranium will turn into lead.
Thus, we can try to calculate the ratio uranium lead in a mineral to know how many half lives
have passed since that mineral appeared.
A very good mineral for this is zircon.
One of the reasons is he is very resistant.
The other materials are weathered, they go away, but it remains practically intact.
And the zirconium that is the element that gives the name to the zircon is very similar
to the uranium.
So that uranium may occasionally enter the zirconium site in the zircon crystal formation
process.
So if we have zircon grains it is possible for example.
Dissolve them in acid making possible the separation of the elements.
Thus a mass spectrometer is used to measure them.
Or I can use a more sophisticated technique.
Like that image here.
This image shows individual zircon crystals that can be placed on an ion microprobe.
This is a device that launches an ion beam into the crystals and draws a sample of what
is evaporated from these crystals.
And yes these samples can be considered as closed elements.
That is, no uranium or lead has entered or exited since the formation of the rock.
Okay, but I just talked about uranium.
But this is not the only element that can be used to date a zircon crystal you can use
other elements.
For example, uranium-235 has a half-life of 704 million years.
One example is the thorium 238 which has a half-life of 14 billion years.
As I said, these occur in zircon crystals.
So, you have independent isotopes to date.
On Moon rocks and meteorites, for example, you can use Sumerian 147 that decays into
Neodymium 143 and Sumerian has a half-life of 106 billion years.
I mean, we know how to calculate the age of the zircon crystals.
But there is a problem.
The rocks that we find on the surface of the Earth have for the most part something about
100 million years.
This is due to the plate tectonics that are constantly renewing the rocks of the lithosphere.
However, they have found older rocks with very deep layers that rose before being recycled.
As an example of these rocks that have remained unrecycled during this time we all have the
Acasta gneisses that can be found in northeastern Canada.
For these rocks it was possible to determine an age of 4 billion.
But in Australia, zircon crystals were discovered that were dated 4.4 billion years ago.
Finally, there are numerous studies on the age of the Earth and information from different
parts of the globe.
But there are other sources of information.
The rocks of the Moon for example.
I mentioned the rocks of the Moon and the meteorites that we can date through other
isotopes.
As in the moon does not occur the plate tectonics process.
We can see that even from here.
We have the craters that remain.
That is, it is not geologically active.
You can date the rocks collected on the surface or very close to the surface.
For these rocks of the pollen was found an age between 4.4 and 4.5 billion years.
And today it is a consensus that the Earth and the Moon were formed about the same time.
This helps you get a better sense of the Earth's age.
We know that Earth is at least 4.4 billion years old.
For the things found in her.
And it has the moon and meteorites that were formed, about the same time.
Meteorites may have come from different places in space but many debris from the formation
of our solar system.
And more than 70 meteorites were dated to the same age range as the Moon rocks.
Based on all this information scientists were able to estimate an age of approximately 4.54
billion years.
Good thing this is for today and until the next episode.
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