World's Oldest Rocks???

[Noah]

Geologists Discover World's Oldest Rocks
Found this on CNN just now. How can the rocks on earth be "old" or "new"? Do rocks just appear out of nowhere every once in a while? The matter that makes up the rock is most likely just as old as the universe itself. Maybe they are referring to the rocks that have been unchanged for the longest time?

Noah

[Tormod]

Noah, this is an easy one. The age of the rock is revolutionary because over time, everything erodes. Geology is the very science of understanding rock formations and how the Earth was formed, and they especially try to understand how the layers of the ground were deposited.

So, finding a rock that is almost 4 billion years old tells us (at least) two things:

1) There has been solid material around for at least that much time (which sets a definitive minimum age for our planet)

2) If solid matter has survived for that long, there is also a potential for inorganic lifeforms to have survived as well, although this is of course highly speculative.

It doesn't have anything to do with the age of the basic constituents of matter, which you point out to be as old as the Universe itself. But as an astronomer you also know that stars are born and die, and in the process they create new forms of matter out of these basic constituents.

I'm neither an astronomer nor a geologist, but I still think it's quite cool to know there is material on Earth that has existed for nearly a third of the age of the Universe...

Tormod

[Noah]

Ok, thanks Tormod. I was thinking somewhere in there, but wasn't quite sure.

[lobices]

something is wrong
how can be a rock older than other? All the matter wasn`t made at the same time?

[Tormod]

No, Quim. The matter at particle level is indeed the same. But the rock itself erodes away. So while the particles remain the rock disappears over the ages and becomes sand, pebbles, or is dissolved in chemical reactions.

Rocks are even formed today - consider lava flowing from an active volcano. This becomes rock when it cools.

That's why some rocks are older than others.

Tormod

[lobices]

I accept...what I must have said, is: the particles are the same!...So, the idea remains, because we can "say" that all the things that exist today are the same in the begining, because, for exemple, the rock from the volcano lava, have the particle that was existing in the volcano that exist in the earth that exist in the solar sistem that exist in the galaxie that exist in the universe...the idea is that all we "see" came from a begining point and so the state of the matter is only diferent but...the same...

...cant we think that way?

[Tormod]

Yes, I think that is a valid point. All matter in the Universe comes from the Big Bang, because the sum of matter and energy is constant (as stated in the law of energy conservation).

In the early days, only a few elements were produced, like hydrogen and helium. The heavier elements (like carbon, oxygen, iron) have been produced in the stars. Marcus Chown wrote a great book on this topic, titled "The Magic Furnace". So over time, the fundamental particles become part of more and more advanced molecules. These molecules constantly change because of cosmic radiation. Earth is bombarded by cosmic radiation every day - as you read this sentence, trillions of neutrinos from the Sun pass through the spaces in your body without even touching you!

Over time the particles decay and eventually become energy again. If the Universe does not stop expanding, the energy will be so dispersed that it will, for all practical purposes, disappear.

For more on this, read my review of The Five Ages of the Universe, a great albeit speculative book.

Tormod