Question about the age of the earth - how is it determined.

[Daisy]

By what method have scientists used determined the age of the earth? Are there more than one? Do most scientists agree that the earth is around 11/2 billion years old?

[Tormod]

No, I have never heard that estimate (where did you find it?). The age of the Earth is generally estimated to around 4,5-4,6 billion years.

Here's a link for you:
Age of the Earth

Tormod

[Daisy]

Tomond,

Is it possible that some of earth's oldest rocks existed in the Universe before the Earth was formed? Meaning that the material used to create the Earth is very old, but the Earth itself could be much younger. Scientists are able to date the material that makes up the Earth but can they tell when the formation of the Earth took place?

[Tormod]

I'm no geologist but absolutely all of the material from which the Earth was formed existed before the planet was formed. In fact, all this matter was created shortly after the Big Bang (according to the standard Big Bang theory). The elements have slowly been formed in stars through nuclear fusion (and the heavier elements are the results of supernovas), which is why Carl Sagan could say "we are all made of star stuff".

However, when the Earth formed it most likely went through a period (or even multiple periods) where it consisted mostly of molten lava. It took quite some time for the planet to cool down and gain a planetary crust. Thus it will be difficult to find rocks that are as old as the Earth. We know, by observation and measurement, the approximate age of the Sun by measuring the ratio of hydrogen to helium. As the sun ages, it fuses hydrogen into helium. The age estimate for the sun is around 5 billion years. The sun had a protoplanetary disk (which can be observed around many other stars as well), out of which the planets eventually formed. Comets buzzing around our soular system have been there since the formation of the solar system, and are believed to contain the basic chemicals needed for life to form on Earth. this is the basis for the European Space Agency's Rosetta mission.

ESA: Rosetta Feature

Scientists have found fossils of living organisms as old as 3,5 billion years, and there is evidence for water almost 4,3 billion years ago.

Water on Earth 4.3 billion years ago

So, all in all, yes, scientists can very well estimate how old the planet is, and how it has evolved since the formation.

And PLEASE spell my name right.

Tormod

[Oracle]

how about radioactivity?

[Oracle]

never mind I just saw it was mentioned in the article Tormod posted

[Tormod]

Radioactivity plays an important part - that is what dating is all about, basically.

As a curiosity, the recent ideas that the speed of light has changed in the past few billions of years comes from observations made in a uranium deposit in Africa...I forgot who wrote about this, I'll see if I can find the book.

Tormod

[Oracle]

I read that they also have evidence that the center of our galaxy is a black hole. I should look up to find the article. They mentioned the speed of light slowing too.

[Tormod]

Here is one:
Speed of light may have changed

Tormod

[Oracle]

Our own backyard's news

:-)