Convincing Geologists That The Continents Move (part of history of science in 100 tweets)

CONTINENTAL DRIFT/PLATE TECTONICS

science works by exploring every possible thing with wildly different tools and approaches and find that it all interlocks

Columbus' first voyage into the unknown most certainly doomed to take more months than he had supplies, lucks out and discovers new continent

using the stars on a spherical sky as guide, we begin to map coastlines onto a globe, the coasts of Europe/Africa fit north/south America!

we find rock formations and fossils on both sides of the Atlantic that match each other.

we sound the entire floor of the Atlantic ocean and map its valleys and mountains, we find a ridge in the middle that matches both coastlines

this ridge is hot with fresh magma rising and cooling to basalt, forming new ocean floor

core samples all along the ocean floor, the bedrock is all basalt

the continental crust however is mostly granite with basalt inclusions and folded metamorphosed sediments it has a much more complex history

core samples along ocean floor have deeper and deeper layers of sediment on top as you get closer to the coasts, closer to the coasts is older?

when we discovered radioactive decay, we learned how to tell the age of REALLY OLD rocks. yup, the ocean bedrock is older towards the coasts.

but ocean bedrock is, over all, young, only a few hundred million years old, continents much older, some rock billions years old.


THE ROLLING OCEAN CRUST MAGNETIC TAPE RECORDER:

why not measure the magnetic orientation of rocks? it orients to the magnetic field of the earth when the rocks form from molten magma

in young bedrock, the magnetic field is oriented towards the poles, in older bedrock, not so, either the poles move or the bedrock moved!

map the magnetic fields across the ocean floor! on either side of the ridge, parallel matching stripes, flipping north, south, north, south...

the north and south poles were reversing orientation every few million years?

look at the magnetic orientations of older and older bedrock on continents, they all point to stationary poles if we MOVE the continents!

well? lets go and WATCH the continents, ARE they moving apart?  HELLS YEAH, umm... by half an inch per year.  this takes radio, or radar or satellites

but 1/2 inch a year is enough if you multiply it by the radio-dates of the oldest ocean crust, BINGO, you get the distance between the coasts!

can entire continents REALLY move? how many MORE INTERLOCKING measurements do you want before you are convinced?  this is how science works

half inch out of 3000 miles is like 1 part in 100 million.  to get these measurements to match we are measuring THAT accurately.  SCIENCE!


so, like soup in a pot, the entire earth is gyrating round and round in a series of interlinked convection cells, continents floating on top

theory of plate tectonics interweaves all the disparate phenomena of geology: continents, oceans, volcanoes, earthquakes, mountain building...