Early Archie After all this time he's still trying to figure out whether he likes Betty or Veronica.
Posted on 01/25/2016 10:35:42 AM PST by JimSEA
Earth has some special features that set it apart from its close cousins in the solar system, including large oceans of liquid water and a rich atmosphere with just the right ingredients to support life as we know it. Earth is also the only planet that has an active outer layer made of large tectonic plates that grind together and dip beneath each other, giving rise to mountains, volcanoes, earthquakes and large continents of land.
Geologists have long debated when these processes, collectively known as plate tectonics, first got underway. Some scientists propose that the process began as early as 4.5 billion years ago, shortly after Earth's formation. Others suggest a much more recent start within the last 800 million years. A study from the University of Maryland provides new geochemical evidence for a middle ground between these two extremes: An analysis of trace element ratios that correlate to magnesium content suggests that plate tectonics began about 3 billion years ago. The results appear in the January 22, 2016 issue of the journal Science.
(Excerpt) Read more at sciencedaily.com ...
At some point, Earth's crust evolved to contain more granite, a magnesium-poor rock that forms the basis of Earth's continents. Many geoscientists agree that the start of plate tectonics drove this transition by dragging water underneath the crust, which is a necessary step to make granite.
"You can't have continents without granite, and you can't have granite without taking water deep into the Earth," said Roberta Rudnick, former chair of the Department of Geology at UMD and senior author on the study. Rudnick, who is now a professor of earth sciences at the University of California, Santa Barbara, conducted this research while at UMD. "So at some point plate tectonics began and started bringing lots of water down into the mantel.
Lower magnesium = granite crust cores = plate tectonics. Subduction of water lowering crust magnesium marks the beginning of granite land masses.
It began on April 7th, 203,029,445 BC.
It was in the afternoon, at 3:32 PM.
About tea time!
Not likely. There are plenty of metamorphic rocks far older than 800 million years. Metamorphic rock is almost always in part formed as a result of deep burial during the mountain building process (also high temps and pressure). Mountain building, outside of volcanoes, is a direct result of plate collision, via the plate tectonics process. Some metamorphic on earth are radio-metrically dated as far back as 4 billion years.
Early Archie After all this time he's still trying to figure out whether he likes Betty or Veronica.
...actually, most volcanoes too are the result of plate collision/plate tectonics. But that’s really another subject.
Also metamorphic rocks can have their mineralogical ‘clocks’ ‘reset’ by later periods of plate tectonic activity/mountain building, and so can appear to be younger than they actually are. However, as far as I know, none can be made to appear older than they actually are. And so one with a date of, say, 3.2 billion years, is at least that old. Make sense?
Breezy and warm, as I remember it.
So now we don't only have monkeys evolving into men, we have rocks that evolve.
Is natural selection involved in rock evolution?
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Subduction of water, granitic volcanics, a little time and you’ve got plate margin volcanos. You’ve got it!! As well with the blue schist, etc.
"I remember that. It woke me up.; |
What you won't have is the geological features like the Hawaiian Islands that are produced by a hot spot in the middle of the plate, and exhibiting progressive amounts of erosion as you travel along the chain of islands.
Quite true, hot spot volcanoes are markedly different than those at plate margins or rifts. You can get the two together which gives you something like Iceland. I believe some of the African rift volcanos are a similar combination.
GMT.
There were no time zones back then because there were no trains.
Start date hell. I am worried about the “best if used before “ date.
Did I do that???
Magnesium is soluble and was washed away from the crust into the oceans and back into the mantle. When this began signaled the start of tectonics. The crust, with less magnesium, is subducted along with water and the resulting lava comes back to and near the surface in less mafic, granitic lava which become the core of the continents.
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