If soils are formed by decomposing rocks, how come we still find rocks from thousands of years ago?

And no-one has mentioned the grinding effect of glaciers as they pushed across the land. Much of the clay round us is glacial deposited from all over the West of Britain. There are still bits of rock in it which started off in Scotland.

 

Good one Pal That can be this evenings lecture

 

We were very lucky to have a visit from a retired Geologist (worked in the Oil industry for many years). He had a wonderful time going round the garden with a hand lens, identifying rocks and telling us from whence they had come. We are in the centre of where there was once a huge lake. blocked by a Glacial dam. When the dam melted the water flooded away (down the Wye Valley) and left behind a few Meres and a lot of rocks from the bottom of the glacier.

 

I just took it for granted that everyone knows about something so obvious. Only joking.

Thanks for all the replies.

 

We don't need to bang on about U shaped valleys, drumlins & the fact that Denmark is a huge terminal morraine then.

 

I thought the earth was only 4 billion years old . Is it a meteorite ?
(PS some great Google images if you search for age of universe - I don't understand them but they look great )
While we are on erosion and glacial action . I saw a programme which said the thousands of ponds in Cheshire were formed by the glaciers depositing large lumps of ice as they retreated ? If you look on Google maps there are lots of ponds south of the M56 . We can send Armandii out to check if you want
http://maps.google.co.uk/maps?hl=en&tab=ll

 

Here's a puzzle then to challenge GeoZig.

How do you know a piece of rock is 13.4 billion years old? That would make it one of the oldest rocks in the universe, given that the universe is only 14 billion years old. If I understand correctly, many of the elements on the periodic table didn't even exist then, because we need stars to manufacture the different elements, then die, then new stars make new elements from the debris and so on.

But in any case, this is the bit I don't understand. Lots of things are 'carbon dated', but carbon is one of the oldest elements. Lets say someone carbon date me, they might work out that I'm somewhere between mid thirties and mid forties. But the carbon that's in me is millions and millions of years old surely?

 

Yep, caught out, I said that last night into the second bottle of wine & couldn't be bothered to google it.

The universe is probably 13.7 billion, so my meteor is much younger at 4.6 billion.

I'd just picked a figure out of my head & deducted 0.3 billion years I'll check next time

You are right Dave, your carbon is a lot older, we'd have to go on radioactive decay of uranium & Thorium I think, to get a bigger picture.

A lot of the elements came into being shortly after the universe happened again, when they talk about elements being created they are talking about a very short amount of time geologically speaking.

Carbon dating only works in a certain time frame, much older things can't be dated with that method. It depends on things ingesting C14, an isotope of carbon in the air. When its been eaten, the isotope stops being absorbed from the air & decays at a known rate.

 

Question for our resident geologists.

We have an area in one of the fields 'out back' at work, where we occasionally dig out a little sand if we need some.

The sand contains this thin layer of material which has been puzzling us for a while now. It has a fairly hard, but brittle and flaky texture, and forms a thin band, no more than 2 or 3 inches thick, usually about 2 ft or below the soil surface.
If crumbled between the fingers it has a somewhat 'irony' smell and is dark brown in colour.

The soil type in this area is generally glacial outflow sands and gravels, overlying chalk or clay. Would love to know what this material is and how it was formed and laid down. Any ideas?

 

Called Iron panning, secondary mineralisation where dissolved iron is re deposited when it meets a layer it don't want to go thru.