Seaham: Remembering the Dead EarthCache

On November 17th 1962, the Seaham lifeboat George Elmy capsized with the loss of it's crew and in 1994 this memorial was created to remember those heroes - to remember the dead. It is quite a unique choice of stone for the memorial because if you look closely, the memorial is made almost entirely of the dead - now preserved as fossils.

This rock is actually a perfect place to go fossil hunting in a very easy and accessible place, there are some beautiful fossils on display. This EarthCache draws your attention to these fossils in a simple Earth Science lesson which will allow you to identify the fossils here and think about just how many organisms lost their lives when they were suddenly turned into stone.

Fossils are formed in different ways, but most are formed when a plant or animal dies in a watery environment and is buried in mud and silt. Soft tissues quickly decompose leaving the hard bones or shells behind. Over time sediment builds over the top and hardens into rock. This section will list a few different types of fossils you could see in this type of stone and explain what they would look like and how you might identify them.

Shark teeth are a common type of fossil for a number of reasons. First, shark teeth, like most teeth, are made of dentin, a hard calcified tissue that does not easily decompose. Dentin is harder and denser than bone. In a tooth, the Dentin is surrounded by a very hard enamel shell.

An example of a shark tooth fossil (centre)

Secondly, to maintain a sharp smile, shark teeth are designed to regularly fall out and be replaced. If a shark has 40 or 50 teeth in its front dentition, and that dentition is replaced every few weeks, it takes no leap in logic to realize a shark can go through tens of thousands of teeth in a lifetime. Different estimates for different sharks range anywhere from 25,000 to 50,000 teeth lost in a lifetime. Now multiply that by millions of generations of sharks over tens of millions of years, and presto, shark teeth are the most common fossil. 

Because many crinoids resemble flowers, with their cluster of waving arms atop a long stem, they are sometimes called sea lilies. But crinoids are not plants. Like their relatives--starfishes, sea urchins, sea cucumbers, and brittle stars - crinoids are echinoderms, animals with rough, spiny surfaces and a special kind of radial symmetry based on five or multiples of five. Crinoids have lived in the world's oceans since at least the beginning of the Ordovician Period, roughly 490 million years ago. They may be even older. Crinoids came close to extinction towards the end of the Permian Period, about 250 million years ago. The end of the Permian was marked by the largest extinction event in the history of life. The fossil record shows that nearly all the crinoid species died out at this time. The one or two surviving lineages eventually gave rise to the crinoids still populating the oceans today.

Three different types of crinoid fossil you might spot

In general, crinoids have three main body parts. The first, the stem, attaches the animal to the ocean floor and consists of disk-shaped pieces stacked on top of each other. These stem pieces come in a variety of shapes - round, pentagonal, star-shaped, or elliptical - and each stem piece is perforated in its center. Rarely are crinoids preserved in their entirety: once the soft parts of the animal decayed, sea currents generally scattered the skeletal segments. By far the most common crinoid fossils are the stem pieces.

Brachiopods are marine animals that secrete a shell consisting of two parts called valves. Brachiopods have an extensive fossil record, first appearing in rocks dating back to the early part of the Cambrian Period, about 525 million years ago. They were extremely abundant during the Paleozoic Era, reaching their highest diversity roughly 400 million years ago, during the Devonian Period. At the end of the Paleozoic, however, they were decimated in the mass extinction that marks the end of the Permian Period, about 250 million years ago. This event, known as the Permo-Triassic mass extinction, may have killed more than 90 percent of all living species. It was the largest of all extinction events (larger than the major extinction at the end of the Cretaceous that killed off the dinosaurs). Although some brachiopods survived the end-Permian extinction, and their descendants live in today's oceans, they never achieved their former abundance and diversity. Only about 300 to 500 species of brachiopods are exist today, a small fraction of the perhaps 15,000 species (living and extinct) that make up the phylum Brachiopoda.

A brachiopod fossil

Brachiopod shells come in a variety of shapes and sizes. Sometimes the bottom valve is convex like the top valve, but in many species the bottom valve is concave or occasionally conical. The outer surface of the valves may be marked by concentric wrinkles or radial ribs. Some brachiopods have prominent spines, but usually these are broken off and are found as separate fossils. The shells of living brachiopods typically range in size from less than 0.25 inches to just over 3 inches in length or width. Fossil brachiopods generally fall within this same range, though some adults have shells that are less than 0.04 inches in diameter, and an exceptional few have shells that are 15 inches across.

Because of their worldwide abundance, diversity, and rapid evolution in the Paleozoic, brachiopod fossils are useful indicators of the ages of different rock layers. By matching the brachiopod species contained within rocks deposited in different locations, paleontologists can determine that the rock units were deposited at the same time.

Corals are made up of small invertebrate animals, known as zooids, that look like tiny sea anemones. They feed on small food particles they find in the water around them. Together, many zooids form colonies, many colonies form reefs. Coral reefs can be massive structures, stretching hundreds of miles. The Great Barrier Reef in northern Australia can be seen from space. The oldest coral fossils are over 500 million years old. The earliest forms were different from those we see today and they died out 225 million years ago. Modern corals are still common in tropical oceans.

A coral fossil

Corals are very important fossils. Many corals have a hard exoskeleton made of calcium carbonate. It is this exoskeleton that is usually fossilised. When the coral dies, the skeleton can be broken down to form limestone, the important building stone you see here. Fossil corals also tell us about the past. Since many corals live in warm, shallow sea water, their fossils are good indicators of environmental conditions. This tells us that the area where the fossils were found must have had a much warmer, tropical environment at certain periods in its history.

Rugose corals are a common fossil in Devonian Period rocks. They come in both solitary and colonial forms. Colonial rugose corals are forms in which many individual coralites were constructed directly adjacent to one another, inevitably sharing resources and ecospace. Solitary and colonial rugose corals were probably grew in soft sediment as long as they were able to keep their polyps above the sediment. In this way, the polyp, which was a filter feeder, would be able to sieve detritus from seawater without becoming clogged with suspended sediment. Solitary rugosans were further specialized in their ability to grow as either upright or recumbent forms, creating the forms more commonly known as "horn corals". Some forms appear to have lived attached to hard substrates such as the shells of other marine invertebrates.

A rugose coral fossil

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1) Describe the main fossils the memorial is made from in terms of shape, size, length, width.

2) Look very closely at the patterns/textures you can see in the fossils. Look on the side and the ends of the fossils and describe what you see. What do you think these patterns were originally?

3) Thinking about your answers to both previous questions, identify the main fossils you can see in the memorial stone from the options given. 

4) Look closely between the bigger fossils - you should spot some much smaller fossils. Describe these briefly in terms of shape and size. Do you think these are the same type of fossils (were they young and still growing when they died) or do you think they are a different type of fossil?

5) Finally, given the fossils are found throughout the rock (not just on the surface), and considering the bigger and smaller fossils it contains - roughly how many fossils do you think this one memorial rock could contain? This question is for bonus points as obviously you can't be accurate (it's like a guess the sweets in the jar question) so don't worry about getting it wrong - just make your best estimate. It is just to make you think about just how many creatures could be fossilised in this one bit of rock.

Please avoid including any spoiler photos in your log that show the memorial too closely. Photos nearby in the area are fine. Thank you for visiting the George Elmy Memorial EarthCache.