Sunday, February 27, 2011

Delaware Bay - Part III

At the same time, sediments were eroding from the Appalachian and other inland highlands and were carried east and southward by numerous rivers and streams.  These sediments (colored sugar sprinkles or a dusting of cinnamon, perhaps) gradually covered the faulted continental margin, burying it under layers of sedimentary and volcanic debris – layers thousands of feet thick.  Today most of those rock layers – those that lie beneath the coastal plain and fringing continental shelf - remain nearly horizontal or tilt gently toward the sea.
Even 9000 years ago, what we now know as Delaware Bay, was still not there – it was yet to form.  However, at that time in the earth’s history there were constant crustal movements along parts of the eastern seaboard.  This uplifting of the coast came about as a result of several tectonic events such as mountain building and continental rifting.  It was also propelled by geological changes such as volcanism, erosion, or deposition (the laying down of sediment).  At the same time, the sea was spreading over parts of the land - in fact, there was an oceanic rise of about one inch per decade (more melting ice cream).  In other parts of the Atlantic seaboard a combination of powerful geological forces such as regional crustal subsidence (the motion of the earth’s surface as it shifts downward) and a change in sea level caused by melting glaciers and tectonic movements created other geological formations such as bays, inlets, and harbors.  In short – the earth went down, the sea went up.
The waters along the Atlantic seaboard continued to rise until approximately 3000BC…then they stopped.  The rising sea drowned the ancient Delaware and Susquehanna river valleys, transforming them into what is presently the Delaware and Chesapeake Bays.  Finally, about 2000 years ago, the earth – perhaps tired from all its geological labors - rested (if only momentarily) and the cartological boundaries of the Delaware Bay were established into their present-day configurations.
And the cherry pie?  It is finished!

In Part IV of this story we'll take a look at the discovery of Delaware Bay...and how it got its name.

Tuesday, February 22, 2011

Delaware Bay - Part II

About 280-230 million years ago (Late Paleozoic Era until the late Triassic) the continent we now know as North America was continuous with Africa, South America, and Europe.  They were all part of an enormous supercontinent known as Pangaea.  Then, as part of an enormous crustal dance, this supercontinent began to break up sometime in the early Mesozoic Era (251.0 to 65.5 million years ago).  It was like a colossal cosmic fork cutting into a slice of our cherry pie – separating this wedge of geological dessert into two parts.  As one section slowly separates from the other, cherry filling oozes and seeps from the crack – a temporary “valley” has formed between the two segments.
In the evolving earth, a three-pronged fissure deliberately grew between Africa, South America, and North America – gradually ripping Pangaea apart.  Cleaving began as magma (cherry filling) welled up through a weakness in the crust, creating a volcanic rift zone.  Powerful eruptions spewed enormous masses of ash and volcanic debris across the landscape as the severed continent-sized fragments of Pangaea slowly, ever so slowly, diverged.
Then, sometime during the Jurassic Period (199.6 to 145.5 million years ago) the Atlantic Ocean began to form between North America and Europe (To carry our geological metaphor one more step let’s imagine some vanilla ice cream melting into the rift zone between our two portions of cherry pie.).  The Eurasian Plate and the North American Plate continued to separate.  Between them was a plate boundary (now known as the mid-Atlantic ridge)« which provided the raw volcanic materials for the constantly expanding ocean basin.  Somewhat later, South America and Africa also began to drift apart (look at a map of the world and you will see how they might fit together, even today, much like two gargantuan jigsaw puzzle pieces; or, if you will, two oversized portions of slightly deformed cherry pie). 
Meanwhile, what is now North America was pulled westward - away from the rift zone.  The thick continental crust that made up the new east coast eventually collapsed into a series of down-dropped fault blocks that roughly parallel today's coastline.  At first, the hot, faulted edge of the continent was high and buoyant relative to the new ocean basin.  But then, as the edge of North America moved away from the hot rift zone, it began to cool and subside beneath the new Atlantic Ocean.  This once-active plate boundary now became the passive, trailing edge of westward moving North America.

[Part III of our story will continue in the next posting.]

« This ridge now extends from a point northeast of Greenland to the Bouvet Triple Junction in the South Atlantic – a distance of approximately 6,200 miles.  It is currently the longest mountain range in the world. 

Friday, February 18, 2011

Delaware Bay - Part I

            Imagine an annual celebration at your house – a special end-of-the-year holiday fĂȘte or a grand summertime reunion.  Scores of relatives and neighbors and friends – some from distant parts of the country - descend on your home to eat and drink and laugh and generally make merry.  For most of the day you feel like the ringmaster of a traveling circus trying to keep everyone hydrated and fed and entertained over the course of several very hectic hours.  Sometime during the festivities you and your spouse step outside for a “breather.”  You look at each other and with a heavy sigh pose the inevitable question, “How did this get to be so crazy?” 
Interestingly, that’s a question scientists have been asking about Delaware Bay - the largest spawning area in the world for horseshoe crabs. 
For now, let's imagine a mouth-watering, taste-tempting, genuine home-made cherry pie.  Think about that oh-so-sweet pie as it’s baking in the oven.  Smells are wafting through the kitchen, down long hallways, and out into the garden.  The pie is gradually and gently turning a rich golden brown; and after about 30-40 minutes a small rift – a crack – begins to appear in the crust.  Over the course of the next ten minutes or so the rift grows a little longer and just a little wider.  Soon, a lava-like glob of rich-red cherry filling bubbles out of the crack, cascades over the fluted edge, and onto the bottom of the oven.  Minute by minute additional blobs of cherry “lava” bubble up like thickened primordial ooze.  By the time the pie is ready to be pulled from the oven the crack has grown wider, longer, and most definitely “oozier.”
The scenario above is one I share with students in my science courses – particularly when we begin our discussions on plate tectonics, volcanism, and the early history of the earth.  Its imagery is immediate and sensory.  Most importantly, it is a  memorable (and most delicious) way to begin our journey into the past.
I tell students that the earth is not a static entity – it is constantly in motion; it is forever sliding, shifting, moving.  Tectonic plates continuously grind their way over and under each other, earthquakes rip through the earth’s crust with daily regularity,« volcanoes belch molten lava from subterranean bowels (just like our cherry pie), and wind and waves sandpaper the fragile surface time and time again.  The earth changes – it is never exactly the same from one day to the next, and certainly not from one eon to the next.
It is constantly evolving.

Our story continues in Part II - the next blog.

« The US Geological Survey estimates that several million earthquakes occur in the world each year. Many go undetected because they hit remote areas or have very small magnitudes. The National Earthquake Information Center now locates about fifty earthquakes each day, or about 20,000 a year.

Saturday, February 12, 2011

Web Sites You Need to Know

As part of the research for the book Horseshoe Crab: A Biography of the Creature Older Than Time, I am also collecting some resources for folks to use in their quest for more knowledge about this unique critter.  Here are some you'll want to check out - particularly now as we begin thinking about all the activity that will be taking place in May and June.
     This is the one!  If you want to know anything about horseshoe crabs and can only check out one site, this is it.  It's got resources, research, information, data, and tons of "goodies" for any "crab-ophile."
     This site features a section of the University of Delaware Sea Grant Program's web site geared to horseshoe crabs.  Cool!
     This is the home page for the U.S. Geological Suvey-coordinated Delaware Bay spawning survey and tagging project.  It includes info. on how you can get involved.
     This is the Maryland Department of Natural Resources "Raising Horseshoe Crabs" project site.  It includes info. on how Maryland schools can get involved.
     This are the Brookdale College Ocean Institute's horseshoe crab pages focusing on horseshoe crab larvae and juveniles.  Lots of great photos here!

Enjoy these sites.  Please let me know if you encounter others - I'd like to share them with as wide an audience as possible.

Sunday, February 6, 2011

Fantastic Facts - Early Life

I am constantly amazed by the anatomy and physiology of horseshoe crabs.  But, equally amazing is their early life.  When you consider that fewer than one horseshoe egg out of 130,000 survives to adulthood, then the early life of a single individual has to be considered much more than astonishing - it is simply incredible!  Here are a few random facts (about a horseshoe crab's beginnings) I've collected in my investigations - in no particular order.  Please feel free to suggests others you feel to be equally compelling.
* A female may lay up to 100,000 eggs in a single nesting season.
* One hoseshoe egg can fit inside this O.
* During an egg's first day, there are eight distinct stages of development.
* In Delaware Bay embryo development may last from two weeks to several months.
* The embryo molts four times inside the egg.
* New larva swim upside down - paddling with their legs and book gills.
* Horseshoes molt 5-6 times in their first year.
* Horseshoe crabs eventually go through 18 stages of development.
Yes, they are truly amazing critters!!