Salt of the Earth: The Source of Sodium and Chlorine in Our Oceans

As an adult, I sometimes forget to ask the obvious questions.  Kids, though, they have their heads on straight.  Living near the coast, I have the opportunity to visit the ocean pretty often.  Every once in a while I brave the frigid waters, and inevitably taste the salty sea, but I never really think about where it came from.  

Recently, I chatted with a friend about her grade school classroom.  She shared some of the science questions her students had asked.  "Why is the ocean saltier than a lake, even though it's bigger?"  I gave her the spiel: lakes and rivers have salt, but water moves through most lakes (and all rivers).  Most of that water, including salts, end up in the ocean.  Water has an easy route out of the ocean: evaporation.  Salt has no such egress.  It stays put.  Just like the ocean, some lakes and seas without outflows collect large amounts of salt. Therefore, we have Salt Lake in Utah, or the Dead Sea in Europe.  I imagined the students' next question: "Where did the salt come from in the first place?", and realized I didn't have a clue.

There are clues however.   The first is the quantity of elements in the Earth's crust.  The most common elements in sea salt vary greatly in their places on the list of most common elements in Earth's crust.  Sodium weighs in at number 6, while chlorine doesn't even make the top 20.  Sodium, therefore, is in everything.  Wikipedia lists 139 minerals, that are composed in part of the element.  When granite breaks down in water, a mineral group called feldspar releases its sodium to the water, and the water doesn't let go.  This weathering of feldspar, and other sodium minerals, would have delivered plenty of sodium to the Earth's oceans very early in their history.

Being rarer in the crust, it might seem that chlorine levels wouldn't be nearly as high in the sea.  In the ocean, chlorine content surpasses sodium as dominant element.  Why the strange ratios?  As it turns out chlorine doesn't play well with others.  A chlorine ion, which is a chlorine atom that has stolen another poor atom's electron, is large, at least relative to other common elements on Earth's surface.  The patterns these smaller ions create don't leave room for the hefty chlorine.  Chlorine elopes with a free hydrogen ion, and escapes out a volcanic vent, having never formed a rock mineral.  At the surface the hydrochloric acid splits, with the hydrogen joining oxygen to make water, and the chlorine dissolved in the ocean.  As chlorine atoms throughout geologic history jostled their way to the surface through volcanoes the oceans grew saltier.

Curiosity has always driven my study of geology.  But sometimes I forget the obvious.  The next time I visit the ocean and watch the surf gather on the shore, I'll be thinking of dissolving rock, belching volcanoes and the rivers that  bring their remnant salt downstream, my borrowed childlike wonder having been appeased.

Lorence G., Collins. "Time to Accumulate Chloride Ions in the World’s Oceans." Reports of the National Center for Science Education 26.5 (2006): n. pag. California State University Northridge. Web. 22 May 2014.

"How did the salt get into the oceans at the beginning of their formation?." UCSB Science Line sqtest. University of California, Santa Barbara, n.d. Web. 22 May 2014. <http://scienceline.ucsb.edu/getkey.php?key=2968>.

Groundtruth: Finding Annual Moraines in My Backyard

An annual glacial moraine.

Twenty-one thousand years ago glaciers covered the northern part of the globe.  Their end point in New England can be seen by following the line of Long Island, New York across to Cape Cod and Nantucket.  This relatively straight line is an artifact of the melting edge of the glacier dropping rocks and sediments delivered from the northern part of the globe, year after year.  As the pile of rocks got deeper and deeper it laid the foundation for these scenic places in New England.  Over time the Earth warmed and the glacier receded back to Maine, but it wasn't consistent.  Each winter the glacier moved forward a bit, and each summer it backed off.  Yard by yard and year by year it retreated to its current (not-so) stronghold at the North Pole.

LiDAR image of annual glacial moraines in West Falmouth.The
image above represents about a third of a mile from north to south.

A month or so ago, I ran into a former student who was researching the glacial history of Maine at Bowdoin, and he introduced me to LiDAR (Light Detection And Ranging) hillshade images that are available for large portions of Maine, including my own backyard.  What he revealed was that with the current imaging technology, we could see not only the large scale features, like Cape Cod, but the yearly inchings of the glacier. Unfulfilled with the images on the screen, I went out into the woods to groundtruth the pictures I saw.  Small hills and low areas I have walked over for years without really thinking about their origin were shown to be moraines dropped each summer by the ice sheet as it receded northward.

Looking up a moraine from a lowpoint in the terrain.

Besting Goliath: The Formation of the Pawtuckaway Ring Dike

The Massabesic Gneiss looks like ice cream
swirled with fudge because of heat and
pressure from 500 million years on the surface

It's hard to dodge the mythological when you look at maps of Pawtuckaway State Park.  Some refer to it as the Dragon's Eye, and for good reason; the park features concentric rings of mountains, identifiable as the iris and cornea.  To see it might even conjure up thoughts of a volcanic Mordor, and as it turns out, 150 million years ago, you wouldn't have been all wrong.  Perhaps the best metaphor for the origin of this strange structure is not literary, but biblical.

The Massabesic Gneiss was Goliath.  Forged in the tectonic rift that cleaved coastal New England from its former mooring point in an ancient Africa, it survived a trek across a long vanished ocean and 500 million years of survival at the surface of the Earth.  Its bold endeavors are catalogued in folds left by heat and pressure along the way.

The ice on the trail is a good metaphor for the park.  As the pool
of magma melted the land below, and added weight above.the
land gave way, allowing magma to rise up through the crack.

Massabesic's David, was not a sling, but a hotspot.  A sedentary warm point deep below Earth's surface regularly created blobs of magma that rose upward.  As the continent shifted with the movement of tectonic plates, these blobs left a string of volcanic mountains including Mount Royal in Montreal and Mount Washington farther north in New Hampshire.  Piercing the Massabesic Gneiss would be different.  Per usual the blob rose toward the surface.  Instead of erupting, the magma sat near the surface, weakening the gneiss's structure from below.  A small eruption may have penetrated the enduring rock.  The added weight, like our misplaced feet, was enough to plunge the Massabesic gneiss into the magma below.  David had bested Goliath.

The gabbro that makes up Meloon Hill flowed up through the
cracks left when the roof of the magma chamber collapsed

Over ten million years, this crack in the armor became a passageway for eruptions of magma that had bided their time.  Magma would have oozed up through the cracks that separated the sunken gneiss from that which remained.  An arc of dark colored, large grained rock, called gabbro, confines the southwest part of the Dragon's Eye.  A disk of salt and peppered rock, called diorite, underlies the lowlands.  These darker rocks may have recollapsed and remelted.  This newer, purer magma would have seeped through cracks to form the whitest, hardest rocks in the park: monzonite. 

Millions of years of erosion laid waste to the softer diorite, and shaved quite a bit off of the gabbro.  The monzonite, more resilient than the rest, remained.  Its stark cliffs are now a monument to the epic battle between a seasoned champion and a literal under...dog.  That is, until a new champion arises.

The view from one monzonite ridge to another.
In the middle are the diorite lowlands. 

Dorais, M. J.. "The Massabesic Gneiss Complex, New Hampshire: a study of a portion of the Avalon Terrane." American Journal of Science 301.7 (2001): 657-682. Print. 

Eby, G.N.. "Mount Pawtuckaway Ring Dike Complex." Geology of the coastal lowlands, Boston to Kennebunk, Maine. S.l.: New England Intercollegiate Geologic Conference, 1984. 240-248. Print. 

McGarry, MaryAnn. "Volcanoes in New Hampshire ." Plymouth Portfolio. Plymouth State University, 17 Nov. 2012. Web. 19 Apr. 2014. <http://www.plymouth.edu/eportfolio/view/view.php?id=12819>. 

Reidy, Daniel E.. "Jurassic Period." New Hampshire Geology Home Page. N.p., n.d. Web. 19 Apr. 2014. <http://www.nhgeology.org/>. 

Reunion on Old Orchard Beach

I hadn't taken into account that water has a way of exploiting a weak point.  On geologic maps, a black line with arrows on one side suggests one slab of rock has slid underneath another.  I convinced my wife to drive out to the site of the fault, with the added enticement that it intersected the coast.  A trip to the beach, on a day above 40 in the winter was not to be passed up.  We pulled into Ocean Park, and while my wife fed my son, I scouted the site.  

What I hoped to see was a reunion.  Five hundred million years ago the rock to the south of Ocean Park and the rock to the north found their home on the fringe of a continent called Gondwana. The goliath Gondwana covered an area of Earth a tad bigger than modern Asia centered around the South Pole.  If Gondwana was Asia, then Biddeford and the rock to the south of Ocean Park were part of Japan; Old Orchard, and the rock to the north,the coast of China.  Four hundred ninety million years ago, plate tectonics ripped Gondwana apart.  These hunks of land set sail across the proto-Atlantic, their near hundred million year journey landing them on Maine's coast 400 million years ago.  Unfortunately, tectonics did not set them gently on the coast.  The force of the plates shoved the edge of the Biddeford land mass underneath the one that underlies Old Orchard.  In a moment I could see Gondwana reunited on Maine's shores.

As I climbed the dune to get a view of this collision, I'd already began to lose hope.  The wind blown sand pointed to the fact that no natural bedrock hindered the movement of sediment. Cresting the dune, I saw beautiful beach for miles in either direction, but no fault.  My wife enjoyed the beach, my son gleefully played in the sand and I pursued the only rock bigger than a pebble, only to be chased away by cold waves.  I looked up the beach at Prout's Neck, and down at Biddeford Pool, wistfully considering my chances of convincing my wife to add some miles to our trip.  If I could just see the rocks on either end, I might find evidence of the Gondwanan meeting point.  Why were they so far away?

A wave hit the shore and my mind traveled back that 400 million years.  That wave would have hit the junction of those collided islands.  It would have found the minute space in between that ancient Japan and that forgotten China.  As it rushed in it would have torn away the smallest piece of sediment.  As it poured out, it would have stolen another.  The space in between would have grown larger and larger. Grain by grain it would be filled in with the small fragments that were broken away.  For 400 million years, the trend would continue.  The end point of this scenario had become clear.  

As we walked back down the beach, on the way to our car, I looked at Biddeford Pool and Prout's Neck as stalwart survivors of an intense collision, then a slow bleed.  Each a reminder of a reunion too long ago to have withstood the relentless abrasion of water.

"Avalon Terrane Field Trip." MIT Geology Field Camp. MIT, n.d. Web. 16 Mar. 2014. <http://web.mit.edu/12.114/05_fall/www/nonGIS_data/worlds_end_bos_basin_field_guide_sm.pdf>.

Dorais, Michael J., Robert P. Wintsch, Wendy R. Nelson, and Michael Tubrett. "Insights Into The Acadian Orogeny, New England Appalachians: A Provenance Study Of The Carrabassett And Kittery Formations, Maine." Atlantic Geology 45.0 (2009): 50-71. Print.

"Geology of Massachusetts." Wikipedia. Wikimedia Foundation, 22 Feb. 2014. Web. 16 Mar. 2014. <http://en.wikipedia.org/wiki/Geology_of_Massachusetts>.

Nance, R. Damien. "Late Precambrian–early Paleozoic arc-platform transitions in the Avalon terrane of the Northern Appalachians; Review and implications."Geological Society of America Special Papers 245 (1990): 1-12. Print.

Osberg, Philip H., Hussey, Arthur M., II, and Boone, Gary M. (editors), 1985, Bedrock geologic map of Maine; Maine Geological Survey (Department of Conservation), scale 1:500,000  

Maine Geology Timeline

I tend to write blog posts in the order I become interested in them.  I may include how long ago events occurred, but when you're dealing with hundreds of millions of years, things get a little abstract. Today I decided to present the information of my blog in timeline form.  Using a web tool at knightlab.com, I created this.  There are some limitations in the software - primarily, the timeline tool does not go back in time to millions of years ago, so I did some messing around with dates to make it work.  Try clicking the arrows on the slides or clicking around the timeline itself to navigate Maine geologic history.  Also, click the links on the slides to find more about each event and how it shows up in the Maine landscape.  Enjoy.

How to Make Bricks in Three Easy Steps

Last weekend my son and I foresook our weekly grocery shopping trip at the West Falmouth Hannaford.  Instead we crossed the bridge on the south end of the parking lot and ended up taking a walk on an ancient sea floor.  Don't get me wrong, this is not a magical bridge that can transport one to a fantasyland.  The bridge was built in 1859 by the railroad company to connect the Hobbs farm to the rest of society.  John Hobbs homesteaded the land in 1775, and before 1859 when the railroad isolated it and the Hobbs sold it, put it to a variety of industrious uses.  Like people of earlier times are fabled to have done, the Hobbs put every part of the land to use.  The trees became oak shingles, the soil was farmed and the clayey sediment was extracted to make bricks.  The story of these bricks extends far beyond the Hobbs enterprising spirit and thousands of years before the clay was first dug.

The story of our bricks began about 22,000 years ago when glaciers covering much of the globe decided to call it a day and begin the slow commute home from Long Island, New York (Long Island formed as the flowing ice of the glacier delivered gigantic piles of rock to its melting endpoint).  At this point, Maine and the rest of northern North America were buried in ice. Heavy, heavy ice.  The normally firm raft of rock, on which our continent sits, sank like a rowboat upon boarding.  As melting glaciers contributed to a growing ocean, this depressed plate would make way for the intrusion of a sea much larger than today's Atlantic.

The land above the sea couldn't wait to cast off its icy water.  Massive streams poured tons of melted ice into the growing sea, but the water didn't come alone. As the rivers raced to the sea their fast current picked up every stone, pebble, sand grain or mote of clay they could carry.  Massive material, like stones and pebbles may have been dropped long before reaching the sea.  When the stream met the water, it rapidly decelerated. Upon slow down, enough sand was dropped to create a river delta as deep with sand as a football field is long.  The sand from this river's mouth can still be spied along I95 between Gray and Lewiston and is currently being quarried in Gray.  But what about the bricks?

The slow moving water, at this point, would have dropped nearly everything.  Robbed of most of its energy by the trudge into the ocean, the sluggish water couldn't carry much.  Luckily, clay is small and light.  The water transported these small grains the farthest, finally dropping them at the sight of the future Hobbs' farm.  About 13,000 years ago, with the weight of ice removed, the plate rebounded, and the sea level dropped.  The acreage of the Hobbs' farm was revealed.  Soil developed.  Oaks grew.  Eventually, the Hobbs would dig up their bricks and my son's and my weight would leave footprints in the ancient seabed.  

McCully, Betsy. "Ice Age." New York Nature. N.p., n.d. Web. 11 Feb. 2014. <http://www.newyorknature.net/IceAge.html>.

Robinson, Michael A., Stewart K Sandberg, and Kirkpatrick Melissa D.,. "Using transient electromagnetic soundings to map the thickness of the Gray Delta, Maine, and correction of data using coil calibration to improve resolution. ." Geological Society of America Abstracts with Programs 33.1 (2000): 1. Print.

Weddle, Thomas K., Gray Quadrangle, Maine, 1:24,000, Augusta, ME: Natural Resources Information and Mapping, Maine Geological Survey, 1997.

"Surficial Geologic History of Maine." Maine Geological Survey. N.p., 6 Oct. 2005. Web. 11 Feb. 2014. <http://www.maine.gov/dacf/mgs/explore/surficial/facts/surficial.htm>.

"River Point Conservation Area." The Town of Falmouth . The Town of Falmouth , n.d. Web. 11 Feb. 2014. <http://www.town.falmouth.me.us/pages/falmouthme_parks/trailmaps/RiverPoint>.

Maine's Pinatubo: Unearthing a Natural Disaster

Soon J.D. Irving Limited may be freed to start thinking about how to take 22 million tons of copper ore out of the ground in northern Maine. The Maine legislature may relax laws regulating the mining of metals in Aroostook County. While Irving consider strategies for extracting copper and zinc, as well as relatively small amounts of gold and silver, I have been thinking about how the metal rich rock, called sulfide ore, got there in the first place. It all occurred about 500 million years ago when a series of islands, not too unlike the Philippine islands, were forming off the coast of North America.

The best lens from which to consider what went into creating the ancient ore might be to consider a more recent event. Twenty-one years previous to the bill being passed, Mount Pinatubo was cooling off after a long summer of letting off steam. In the summer of 1991, the Philippine Sea Plate subducted beneath the Eurasian plate, releasing 10 billion tons of magma in a volcanic eruption. As the magma neared the surface, it released chemicals that refused to join with others to form minerals. Valuable metals, like zinc and copper and dangerous ones like cadmium and lead, were distributed as ash across the Philippine region. Far from a rain of wealth, the ashfall is thought to have significantly shortened human lifespan on nearby islands. Sulfur combined with oxygen in the atmosphere to form sulfur dioxide gas, which in turn joined with moisture in the atmosphere to form sulfuric acid. Aircraft throughout the Northern Hemisphere experienced corrosion damage from the acid for years afterward. It is with good reason that the eruption of Mount Pinatubo was regarded as a natural disaster.

Five hundred million years ago no one was around to experience the ash or acidity of eruptions that formed the islands that would become the metal-rich rock in northern Maine. The islands and the ore formed as two oceanic plates in a proto-Atlantic ocean collided. One plunged beneath, bringing loads of ocean water with it. As the water and the rock descended, both heated. The water would have rushed through subterranean rock, dissolving unmatched elements along the way. The scalding liquid would have picked up sulfur, then metals. It would wend its way upward, cooling as it went. As its temperature dropped the dissolved sulfur, submerged and lacking its partner oxygen, would seek out other mates, finding them in the unmatched metals that flowed alongside. The sulfur/ metal pairs, sulfides, solidified and were stored underground preventing life's exposure to corrosive acids or dangerous metals.

In the next decade J.D. Irving may decide it is worth unearthing the metal-bearing sulfides of Aroostook County. But the price of digging up a natural disaster must be paid. Payment can be rendered in advance if the mining company works to prevent the spread of sulfur and metals into the environment. It can be paid after the fact by the citizens of Maine, in the form of clean up costs. Or, it can be paid by sacrificing the beauty and balance of northern Maine's natural ecosystem. Regardless, the cost must be rendered, and it's best to consider this before the bill comes due.

Beck, Fredrick. "A History of Non-Ferrous Metal Mining and Exploration in Maine." Geological Society of Maine. N.p., n.d. Web. 1 Jan. 2014. <http://www.gsmmaine.org/wp-content/uploads/2010/02/Beck-A-History-of-non-ferrous-metal-mining-and-exploration-in-Maine.pdf>.

Casadevall, Thomas J. , Perla J. Delos Reyes, and David J. Schneider. "The 1991 Pinatubo Eruptions and Their Effects on Aircraft Operations." Fire and Mud: Eruptions and Lahars of Mount Pinatubo. U.S. Geological Society, 10 June 1999. Web. 1 Jan. 2014. <http://pubs.usgs.gov/pinatubo/casa/>.

"Environmental Health and Safety Guidelines Base Metal Smelting and Refining." International Finance Corporation. International Finance Corporation, 30 Apr. 2007. Web. 1 Jan. 2014. <http://www.ifc.org/wps/wcm/connect/4365de0048855b9e8984db6a6515bb18/Final%2B-%2BSmelting%2Band%2BRefining.pdf?MOD=AJPERES&id=1323152449229>.

"Open-pit Metal Mining in Maine." Natural Resource Council of Maine. Natural Resource Council of Maine, n.d. Web. 1 Jan. 2014. <http://www.nrcm.org/issue_mining.asp>. 

"Volcanic Gases and Their Effects." Volcano Hazards Program. U.S. Geological Survey, n.d. Web. 1 Jan. 2014. <http://volcanoes.usgs.gov/hazards/gas>. 

"Volcano or Environmental Disaster?." VolcanoCafe. N.p., 18 Nov. 2013. Web. 1 Jan. 2014. <http://volcanocafe.wordpress.com/2013/11/18/volcano-or-environmental-disaster/>.