Chalk cliff formation?

Question

On average, how long would it have taken to form a metre of chalk cliff at, say, Dover?

Answer 1

Yes, a slow process. Something I often quote when faced with the village idiots who insist the earth is less than 10,000 years old!
Chalk forms very slowly by definition. . There is an old geologists maxim "The present is the key to the past" Calcareous (Chalk and limestone ) deposits are being formed today , under warm calm tropical marine conditions.We can actually watch it happening. we can send drills down to the sea bed, collect samples of the limy mud as it accumulates and measure the thickness of it. Catastrophic evens are not conducive to chalk/limestone formations.
Answers in Genesis is funnier than Monty python. The section about Plate Tectonics is hilarious ( According to them,the plates used to move a heck of a lot quicker than they do now, that is why the Atlantic ocean has managed to widen out in only a few thousand years ,not 60 million, but now, surprise surprise, they have slowed down ) There are so many lies in there, Joseph Goebbels would have been proud of it.

Give grpr1964 the 10 points. Perfect answer!

Answer 2

Would be good if people would keep religious opinions to the religious section of Answers, and let people with some scientific knowledge and training have a bash at answering the questions here. If you have a close look at chalk formations like you find at Dover, you'll see many distinct beds and formations, it wasn't deposited in a single flood event.
It's very funny reading 'creationist geology' - but it's nonsense.

Answer 3

They say chalk deposition at White Cliffs of Dover spanned 30 to 35 million years, at a "speed" of about half a millimetre a year.

Answer 4

I would imagine that 1mm per year, possibly less, would be a fair estimate, given the thickness of the chalk and the known time period involved (tens of millions of years).

The present isn't exactly the key to the past on this one, as the chalk was formed from algal skeletal material (coccoliths) during a period of exceptionally warm climate and high seal level during the late Cretaceous period (we would need a great deal more global warming to replicate this!). Ironically, this would have been the mother of all "floods", albiet one that lasted many many orders of magnitude longer than anything you could sail an arc on. Anyway, there being no nearby exposed landmasses closer than North Wales or Devon and Cornwall, a relatively pure white limestone was able to accumulate over long time periods. Bear in mind (in any calculation of depositional rates) that there will have long been periods of non-deposition (leading to fossil-encrusted "hard-grounds" or miniature unconformites), draped by pelagic deposits (the gradual settling out of the coccolith skeletons), or more rubbly slumped chalks (catastrophic beds induced by earth-tremors), or more muddy (marly) chalks.

The beautifully-preserved fossils that come from some chalk beds are simply due to preservation under periods of very quiescent depositional environment, quite probably under anoxic bottom-water conditions. However, there are plenty of other beds where broken up and badly-preserved fossils testify to periods of sediment re-working under more energetic environments.

PLEASE DO NOT believe anyone that tells you that just because the chalk is pure and apparently homogeneous-looking, that it was somehow created in a single (>biblical) event. For a start, homogeneous it most certainly is not! The chalk, in detail, is often not that pure, and often has shalier or even silty layers within it. The geology is often remarkably complex, with considerable thicknesses of slumped, re-worked and re-deposited strata. Really these are turbidite deposits, but made from chalk rather than the more typical clastic material (sand and shale). Under the North Sea, it is much thicker and can reach several kms in thickness in places where geological subsidence permitted sufficient "accomodation space". You can map all of this out in detail from borehole data and seismic images. The chalk gets shalier further north and becomes a calcareous mudstone under the North Sea to the northeast of Scotland.

The chalk is a truly amazing rock, but (for God's sake!) one does not need Biblical explanations to understand its origin or appreciate its beauty!!! This is not an anti-creationist "rant", but is fact, borne out by straightforward scientific observation and mapping.

Answer 5

If the chalk at Dover had formed at a milimetre a year, or some such slow rate, then it would not be pure - there would be evidence of plant growth, mud, etc - such as you see at the bottom of the sea now.
The fact that it is pure is an indication that is was laid down rapidly in a catastrophic event.

More generally, the fact that we find so many (often perfectly formed) fossils is evidence of rapid burial in the surounding rock - sedimentary rocks were clearly laid down by one or more catastrophic event. You don't bury a dinosaur one milimetre at a time over hundreds of years! Dead animals get eaten and rot away in days or weeks.

The link below is a moderately technical creationist article to explain recent creation of chalk at (eg) Dover.
The creation-haters such as above would do well to check their facts rather than just rant :)

Answer 6

A lot longer than the ferry crossing to Calais, possibly 100,000 years. Happy new year