NH Notes: A Fossil Scallop from Calvert Cliffs, MD

A colleague has a fossil scallop in his office that he collected while teaching a field course on Chesapeake Bay biology.  He pulled this scallop from the cliff wall at Calvert Cliffs near Calvert, Maryland. It is particularly impressive not only for its size (more than 5 inches in diameter) but also for its condition.  But what caught my eye was what was attached to it (see below).   This fossil scallop is thought to be not much more than 10 million years old, so is a youngster in geological terms.  As such it demonstrates some features of “younger” fossils that are typically not appreciated.   Let me share some pictures I took of this fossil and then provide the geological context for where it was found.

This was the side facing down.  The top side is more interesting as shown in the images below.

Here is a picture of the topside of the scallop.  Two things to notice here: First, there are several large barnacles that are attached to the top of the shell.  Several of them were damaged during the extraction of the shell from the cliff wall.  The second is an orange discoloration on the top part of the shell and one of the barnacles.  This represents the portion of the shell that was exposed on the cliff face for some time and became stained from chemicals that leached out from the rocks and soil in the layers above and ran down over the face of the cliff.

Just what are the Calvert Cliffs?  They are a long set of cliffs along the western shores of Chesapeake Bay in Maryland south of Washington D.C..   As the bay erodes the cliff wall new fossils are continually revealed and collectors come to find shells, sharks teeth, corals and even the occasional whale bone.   Fossils densities can be very high with many billions of shells certainly preserved here.

Are these really fossils?

Looking at these pictures you may wonder if this is really a fossil or just a shell buried in some sand hundreds or thousands of years ago.   The term “fossil” is not easy to define as the process of becoming a fossil is not made of discrete steps but rather is a gradual process.  The shells here retain much of their original molecules rather than having been replaced by minerals.  So they are not “rock” in the sense of many older fossils.  Nevertheless they are best thought of as fossils because they are imbedded in rock and their chemistry is altered. These are not like shells that you would find on the beach or even shells that are thousands of years old that you could dig out of an old beach in Florida for example.  This fossil scallop is very heavy as it has been at least partly mineralized.

A shot of the base of the scallop showing just how well preserved this scallop is and how the barnacles are attached to it.

The detail in preservation is really amazing

This is a close-up of the ridges of the scallop showing the mineralized surface.

Where did all these shells come from?

Why are there many meters thick layers of rock embedded with billions of shells and sharks teeth found at this location and how old are there?  Look at the picture to the right.  Shells are stacked on top of each other many meters high.  In many locations the shells are mostly broken, show signs of predation like bore holes and are covered with barnacles.  Geologists who have studied this region believe that this entire area was covered by a shallow sea when the Earth was warmer and the ice caps were melted.  At that time shells would have accumulated on the sea floor and especially near shorelines.  Erosion of the Appalachian mountains would have continued to introduce new sediments into the sea covering the shells and allowing for their preservation.  Shells are thought to have accumulated at this location for hundreds of thousands of years.  Eventually the Earth cooled and the ice caps reformed lowering the ocean surface by hundreds of feet.  Erosion via rivers then cut through what was once the ocean bottom.  Today the Calvert Cliffs are one place we are able to see the remains of these layers of sediments now turned to a soft form of sandstone rock  (sandstone is like a fossil, it forms through a gradual process of cementation and this sandstone isn’t well cemented so easily broken and worn).

Creationist’s Geology Challenged Again

I’ve said that geologist believe that the rock layers of the Calvert Cliffs are 8 to 20 million years. Obviously young earth creationists (YECs) can’t accept those dates.  Georgia Purdom, staff scientist for Answers in Genesis, has questioned the age of this formation by questioning the validity of radiometric dating. But she and others YECs completely miss the forest for the trees.  Radiometric dating is just a red herring here.   They need to deal with the actual fossils and what those fossils are telling us about their past.

To compress all the geological formations of the Earth into a few thousand years requires some extraordinary events.  YECs think they have that extraordinary event in Noah’s Flood but does that really explain a formation like the Calvert Cliffs?  Not really.   There are 20,000 feet of fossil-bearing sediments below these cliffs.  Are we to believe that this large scallop with its barnacles survived the turbulence of a global flood only to be deposited at the very top of the geological column without so much as a scratch?  This is not reasonable. In fact, even YECs  who look at the geological context and the condition and types of fossils here would likely conclude they are not the result of a global flood.   Rather would likely appeal to some sort of post-flood events but that would put their origins sometime less than 4500 years ago!  Even so these shells do not appear to be laid down by any large event but by natural everyday processes of a shallow seabed.

Clearly this area of Maryland was covered by a sea and YECs might be tempted to accept this as well but this causes a problem. They have been promoting the theory that there was a global ice age right after the global flood. If this was the case then the ocean levels would have been hundreds of feet lower rather than higher.  There is no place in their theories for the creation of this particular layer of fossils.  These fossils form the remains of organisms that are clearly all from a particular ecological setting. That setting is one of a shallow and very warm ocean that suggests a time when the Earth was much warmer. A warm Earth is completely consistent with the ocean being hundreds of feet higher at this location at the time.   The fossils are all of organisms that are considered modern rather than long extinct things. All of these observations about the Calvert Cliffs fossils are completely consistent with the millions of years old estimated dates of the rock.

So where does this scallop fit into the YEC view? I have no idea and I don’t think they do either.  They will simply avoid the specifics and point to possible issues with radiometric dating as if casting doubt on a date will prevent all other questions.