Tuesday, November 6, 2007

Who (or What) Goes There?

A couple of evenings ago I went for a walk out to Hut Point with Robin. It has been very windy over the past couple of days, and yesterday it was gusting upwards of 40 knots; it was ‘Condition 1’ at several locations out on the sea ice / ice shelf yesterday - see the McMurdo weather information page below:

If you look at the picture below you will see what we saw in the snow around the Hut.

You can see that the footprints left by previous walkers after the most recent snowfall have been preserved, but you will notice that they are standing up above the surrounding snow. Why is this? Well, when we step on the snow we press down on it, this pressure forces the snow crystals to bond together. When the wind picks up, it will blow away the looser snow that has not been stepped on, but the wind is unable to pick up and move the snow that has been bound together in the area of each footprint. Hence the footprints that were formerly depressions in the snow are now sticking up above the remaining snow. This picture is taken looking approximately to the west – what direction was the wind coming from? Which direction was it blowing towards? So we have clear evidence for people walking around the hut. What else could we do to try and figure out who it was that was walking around the Hut?

The picture above is the view looking towards the north-northwest from the Hut. In the foreground you can see pressure ridges that have built up in the sea ice. On some of the warmer days about a week ago some of the ice melted at the surface, forming melt pools; this water has since refrozen.
Tonight (which is Tuesday) some of us are going over to Scott Base (see picture above, taken a couple of weeks ago) for dinner; they have a superb view of some pressure ridges there [note added later: we just got back from Scott Base; we had a wonderful dinner, with great company - the Kiwis had been watching the Melbourne Cup on TV -it is the Australian equivalent of the Kentucky Derby. However, we could not see much outside because the weather had deteriorated to a Condition 2].

The footprints we saw near the hut have a subtle link to some of the features we are seeing in the core. There are places where the sediment we see in the core is disrupted in a way that indicates some kind of bottom-dwelling organism was foraging for nutrients. When these critters leave distinct patterns behind in the sediments, the patterns are called trace fossils. You are probably familiar with the use of the term fossil for remains of harder parts of plants or animals (e.g. shells and bones), which are called ‘body fossils.’ The term Trace Fossil refers to marks or tracks in sediment that result from some behavior by an animal that provides some evidence for the shape and characteristics of the animal. There is, in fact a whole branch of Paleontology (the study of fossils) devoted to the study of trace fossils; it is called Ichnology. The word Ichnology comes from a greek word ‘ikhnos’, which means ‘trace’ or ‘track’. The traces left by various critters are divided into groups that indicate what the critters were doing, i.e. burrowing, boring, footprints, track marks, feeding marks, trails. Trace fossils are tricky to identify in the core, but some of the fossil material we are seeing in the core includes material that looks like this (the creamy white tubes - the picture is about 4 cm wide):
The little white tubes are actually the ‘burrows’ made by serpulid worms; the insides of the burrows were coated with the white material, which is actually a kind of outer shell made by the worm. These worms are quite unusual.

Lets look at some fossils from elsewhere (i.e. NOT in the core, or in Antarctica); the picture here is of some dinosaur footprints; these trace fossils make up a trackway.
The picture below is of human footprints from Laetoli in Tanzania – they are footprints of early hominids. They have been interpreted to record the hominids fleeing from a volcanic eruption. These are Trace Fossils – they are a type of trackway.

Links and Teacher Resources on Trace Fossils
Site has nice simple definitions and some K-12 teaching ideas and activities

General Information and links on Trace Fossils

Information and Classroom Activities involving Fossils

USGS Website with Fossil Information

General Information on Ichnology

A Guide to Ichnology from a Specialist

Guide to Trace fossils from the Hooper Virtual Natural History Museum (Carleton University, Canada)

Information on Coprolites on Hooper Virtual Museum Page

University of Calgary – Information on Trace Fossils

Information on Trilobite Trace Fossils

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