reply to post by kiwifoot
Since i've been reading ATS I've always read some crazy things about geology, and being a geologist is almost heartbreaking.
1. Stop with the expending earth... with enough time i'll demonstrate you why it's impossible, and proof of the earth being a whole solid body but
well, it's already late here (i'm in france), so maybe next time.
2. about the rifting :
first, you have to have a source of heat juste beneath the crust. This source of heat is generally a magma plume, comming up because of archimed's
law and will induce a diminution in the crust thickness. Just like if you were melting a layer of plastic from beneath.
then Volcanism appears, is our case, this is the nexte step commine ahead.
After volcanism, extenstion makes it's move, this is when the rifting really occur.
Then, you began to have a separation, this is the full rifting process, each border of the rift are separating, creating normal faults and the crust
keep getting thinner.
As the borders or lips, of the rift are separating, a sedimentary basin is being created, and sediments beguns to accumulate.
this accumulation will add a weigh on rocks, creating Subsidence (search it!), basically, the basin will sink because of the weight and because of the
heat (this is how you create petroleum, by getting rich organic matter rocks deeper, and you know that deeper you are, hotter it is, so organic matter
can be cracked into hydrocarbures).
Then, as the bottom of the rift is getting deeper, it will pass under the Mean Sea Level, so, water will flood it creating a sea.
Next step, if the extension goes on, you will have an ocean. End of the story.
the way the crust is getting thinner will be the main setting to know if the rift will pursue is opening or not.
We calcul a shortening factor (beta) with the lenght of the crust, if this factor is less than a certain number, rifting will not continue.
3. So yeah, having a rifting will modify the sea level, we call it "tectono-eustatisme" here in France, don't know how to say it in english, sorry
Being simple, as you modify the basin configuration, you will have an effect on the mean sea level.
By the way you can also modify the volume of the ocean...
How ? simply by activating the oceanics rifts, you will then create more oceanic crust thus you change the volume of ocean, more volume for the same
amout of water = decreasing sea levels.
For the one wondering why rifting is usually observed in deep sea, juste remeber that rifting always begins into the continent, then lead to the
formation of a sea, and then at last to the formation of an ocean.
Search for Wilson Cycle, you will understand how it works globaly.
Finally, for those still giving the old propaganda of the hollow earth and the earth in expansion, please, read some more about plate tectonics,
subduction, collision and wilson cycle. I just can stand those people, they are creationist for me. No offence, it's juste that all the creastionist
I've encountered were narrow minded about scientific fact.
I hope my explaination was clear, sorry I do what I can in english and I'm in a kind of hurry to go sleeping at last.
Don't hestitate if you have questions, I may not be the best geologist, but I can surely help understand.
bye ATS I love reading you before sleeping !