Abraham Lincoln was born 350 million years ago, floating in an ancient ocean that covered what is now the western United States.
I’m talking about Abraham Lincoln the statue, of course, not Abraham Lincoln the former President of the United States. Lincoln, and the memorial that he currently sits in, are carved from the desiccated, metamorphosed skeletons of gazillions of long-dead sea creatures.
The Lincoln Memorial, like the nation that Abe presided over, has a rocky history.
We begin our journey on Earth, 1.7 billion years ago. Most of our planet was covered in shallow seas. Anything that was alive was single-celled, and probably living in water, photosynthesizing away, exhaling oxygen into the atmosphere, because really, who needs that stuff? Thankfully, we eventually figured out a way to use that waste product to be alive and stuff, so, thanks!
Around this time, Colorado formed. I don’t mean Colorado, the rectangular cartographic delineation that will one day become the 38th state of the Union. I mean the actual terra firma, the chunk of crust that became Colorado. The earliest rocks that have been found beneath the state date to this aquatic era. These are not the rocks that Lincoln is carved from.
Lots of stuff happened over the next several hundreds of millions of years that, well, we simply don’t have time to talk about.
Here’s some highlights, though: Barren supercontinents like Rodinia broke up and migrated into new and improved supercontinents, land masses began to host life on a larger scale thanks to Earth’s helpful new ozone layer/radiation shield, and eukaryotes joined the party, quickly diversifying into things like insects, plants and amphibians.
But as recently as 340 million years ago, the ocean was still the place to be.
One of those oceans, warm and shallow like a YMCA kiddie pool, stretched over the entire western chunk of North America. It was teeming with tiny, single-celled plankton of many kinds, like these foraminifera, who house themselves in ornate suits of armor made of calcium carbonate:
As these creatures succumbed to the mortal coil, their shells sank to the ocean floor. After hundreds of thousands of years, that calcium carbonate piled up and was pressed into chalk, and that chalk became sheets of limestone several kilometers thick.
Rocks made from (formerly) living things! That’ll teach you not to take chalk for granite.
Quick diversion for the Brits in the audience: A similar shallow ocean covered the area that is now England, teeming with similar chalky plankton called coccolithophores, although I assume they spoke with a slight accent. Their calcium-rich remains piled up as well, eventually becoming the Cliffs of Dover! Southern England is made of dead stuff. Except Dover’s cliffs are only ~80 million years old, compared to 340 million years old for Colorado, so who’s got history now?! BOOM.
Anyway, we have to fast forward past a bunch more of Earth’s history because I’ve got stuff to do. Over the next couple hundred million years, the Ancient Rocky Mountains were thrust up thanks to plate tectonics, eroded away completely, were submerged beneath another ocean, and finally thrust up, up, and up three more times, finally becoming the Rocky Mountains we know and ski on today.
That thick marine limestone was further metamorphosed into Yule Marble by heat from deep inside the Earth. Huge stone blocks that used to be on the bottom of an ocean were quarried from sites than a mile above sea level, then sent by train to Washington D.C. Just look at this stuff:
It was completed in 1922, but the Lincoln Memorial began its life more than a quarter billion years ago. Every fleck of smooth white stone, from beard to boots, used to be a free-swimming organism. And although monuments like this allow us to expand our existence beyond our wee life spans, it too will return to dust.
It’s a gneiss story, no?
Geology pun count = 4. Paleogeologic map of North America during the Mississippian Period (top) by Ronald Blakey/CPGeosystems. If I made any errors, I apologize, I’m not a geologist and accept all fault. Make that 5.
EDIT: I originally said that the Colorado limestone came from coccolithophores, which doesn’t match geologic timeline. Fixed that.
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- geowanderlust said: Ohhh geological history always makes my night. You always see pictures of minerals, rocks, etc but never how they came to be. Kudos.
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