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Hiked Bradbury Mountain. The geology is interesting! It formed in the collision of two ancient continents when the supercontinent Pangaea formed. This was about 360 Million years ago. /1 
2/ On Earth (unlike Mars or the Moon), the crustal plates keep sliding around. We see it happening now as the Atlantic seafloor is getting measurably wider. Continents have repeatedly collided then pushed away like this.
3/ The Atlantic seafloor spreads as new igneous material bubbles up along the Mid-Atlantic Ridge. (Image credit: nytimes.com/2016/01/12/sci… & staff.imsa.edu/science/si/hor…)
4/ Every 300-500 million years, all the continents collide then re-separate in the “Supercontinent Cycle”. If we had a time lapse video, the continents would look like pats of butter sliding on a hot frying pan. Here are the reconstructed supercontinents. en.m.wikipedia.org/wiki/Supercont…
5/ Most of the bedrock of New England’s coast including Maine formed during the last collision as the micro continent Avalonia collided with Laurentia (N. America) then was trapped inside the bigger collision with Gondwana (Africa). See B&C in the picture. en.m.wikipedia.org/wiki/Pangaea
6/ As the picture shows, as the continents collided the Iapetus seafloor had nowhere to go so it was subducted beneath Avalonia. There, it melted and the new magma welled up into Avalonia as new igneous rock (shown in red). This became the igneous rock we see today in Maine.
7/ If magma comes all the way up to the surface then it will cool very quickly and it becomes a fine-grained rock like basalt. There are basalts in Maine. But Bradbury Mountain where we hiked is mostly granite, a coarse-grained igneous rock. It is composed of large crystals.
8/ This means it didn’t come up to the surface as it cooled. It must have been deep underground where it cooled very slowly. That gave the molecules in the magma enough time to diffuse around and join with like molecules, forming the large crystals of quartz, feldspar, and mica.
9/ All the mountains in Maine are erosional remnants. They didn’t form by being pushed up but by rock around them eroding away. Bradbury Mountain was a blob of granite deep underground before the overlying and surrounding, weaker rock washed into the ocean, leaving it exposed.
10/ I think that’s pretty cool. It’s hard to grasp the idea that all this was deep underground, that SO MUCH erosion had to take place to produce what we see now, but 300 million years was a lot of time. It was amazing work by the world’s geologists to figure it out.
11/ You can see evidence how this magma intruded into the preexisting rock of Avalonia about 350 million years ago. It squeezed between the layers of sedimentary mudstone from the Iapetus sea. The magma’s heat metamorphosed the mudstone into mica schist.
12/ Only about 10,000 years ago, Maine was covered by a glacier that flowed from north to south, scraping the rock as it went. Exposed bedrock is usually rounded showing the direction of the glacier’s movement. (My daughter Olivia on a glacier-scraped surface.)
13/ Smooth surfaces are usually on the north side of exposures where the glacier scraped it smooth. Rough surfaces like this are usually on the south side where the glacier broke chunks off and carried the fragments away.
14/ After the glacier retreated, relieving the crust of that huge weight of ice, the land buoyed up and the ocean retreated about 10 miles further offshore from its current location. The islands we see today were just the hilltops, and the bays we now see were broad valleys.
15/ With the glacier gone 10,000 years ago, plants recolonized. Forests grew. Large animals including moose and deer migrated into the region. Then humans moved in, following the large game. There is evidence of at least two cultures in this region over the past 10,000 years.
16/ First, there is evidence of “Maritime Archaic” culture 8000 to 1000 years ago, where humans hunted seals (see picture) and collected clams and berries. We routinely find shellmounds and stone artifacts on shorelines. We see an archaic shell heap on this island, for example.
17/ The Maritime Archaic culture probably includes the Red Paint culture that flourished in much of Northern America including Maine from 3000 to 1000 BCE. It is unknown why the Maritime Archaic culture disappeared. en.m.wikipedia.org/wiki/Red_Paint…
18/ Starting around 1000 BCE, the Míkmaq and Abenaki and other First Nations appeared in this region, members of the Algonquin language group and part of the Northeast Woodlands culture. en.m.wikipedia.org/wiki/Algonquia…
19/ So I know this is a stretch, but this is how my brain works. On a geology hike I started thinking of human cultures because my youngest kids climbed a tree, and I worry they’ll fall and get hurt, but so I notice trees are growing on the granite mound and humans climb them 😅
20/...so that brought the thoughts, how did forests colonize the barren land after the glacier evaporated, how did the humans move in here, and how do we interact with the forest and the rocks beneath it? And so there it is, full circle.
21/21 Tomorrow we drive back to Florida and I’ll be back to working on space. Monday I travel to the In Situ Resources Utilization (ISRU) conference to give presentations on lunar mining and construction of lunar landing pads. Bonus pics: Natalie stole my phone & took these 😅❤️
I am putting my cousin’s row boat back at his cottage and realized I can get a picture of the shell heaps on the shore here. I think these are from the more recent Algonquin culture a few thousand years ago. Zooming in:
