Journey Somewhat Nearer to the Center of the Earth: fossils in cores

Most of the time, when people are looking for fossils, they find them at the surface or just below. However, this is hardly the limit of where they can be found. After all, a fossiliferous formation found at the surface in one location may be buried hundreds to thousands of feet beneath other rocks and sediments somewhere else, and it doesn't stop being fossiliferous just because it's buried that far down. It just becomes much less accessible. We can get glimpses of the buried fossils through core samples.

Regarding forams

Life started out microscopic (at least to humans) and most of it has stayed that way. Of course, many microscopic organisms have poor fossil records, due to factors like lack of hard parts and the whole "microscopic" thing (finding and studying microfossils takes special equipment and expertise that aren't used for collecting, say, brachiopods). However, a subset of microscopic organisms have very significant fossil records. We saw the ostracodes a few years ago, but there are also a number of groups of single-celled organisms that produce hard parts suitable for fossilization. Among the most important are: coccolithophores, phytoplankton which form skeletons of scale-like objects known as coccoliths, micron-scale structures that make up chalk (and which are sometimes called nannofossils because they're so darn small); diatoms, phytoplankton with cell walls made of silica; dinoflagellates, which form organic-walled cysts; radiolarians, protozoans that form body structures of silica; and the subjects of today's entry, the foraminifera, which can be described glibly as "amoebas with shells".

A living foram, the brackish-water benthic calcareous species Ammonia tepida, showing strands of pseudopodia surrounding the coiled test. What do all these terms mean? Read on! (Photo from Wikimedia Commons; unfortunately, no scale, but you'll get an idea of the size of what we're dealing with in the photos to come.)