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Q1. There are four diagrams forming part of the display summarising the events from the time the footprints were formed to the time they were discovered. Please list this sequence.
Q2. How old were these footprints originally estimated to be and what subsequent methods were used to determine their current age?
Q3. There are two other African footprints (not those of animals or birds) mentioned on display. Where were they found, how were they formed and how old are they? Who is believed to have made them?
SOME HISTORY
The story of the famous Nahoon Point footprints started in 1964 when Municipal employees Bill Hartley and Rhett Kayser were doing some work at Nahoon Point near East London. Being a hot day they sheltered from the sun under an overhanging rock, and looking up they saw what looked like some animal tracks, a bird track and three human footprints in the roof. They reported it to Margaret Courtney-Latimer who was then head of the Museum, and on investigation, she confirmed that they were footprints, fossilised in the sandstone. Soon after this, the whole roof collapsed, but miraculously, in one piece.
The huge piece of rock which had collapsed was now lifted and transported to the laboratory at the museum where, using luminescence techniques, (which are far more accurate than Carbon-dating) they dated the footprints to approximately 200,000 years old, this making them belong to the Archaic homonid period. Fossils aged from 200,000 to 125,000 years old are classified as Archaic, less than that, as modern. At first it was thought that the animal tracks were those of some sort of buck, but later they decided that they could be rabbit tracks. To test the theory, they borrowed a rabbit from the zoo and chased it over some wet sand, and sure enough, the tracks were identical! The human footprints are thought to be those of a child of about 9 or 10 years old.
GEOLOGY OF THE EASTERN CAPE COAST
Throughout the Eastern Cape coast, sandy beaches with occasional rocky outcrops predominate. Nahoon Point (and the area around Bats Cave) is one such attractive promontory headland of aeolinite or dune rock. Lesser patches are found along beaches as far north as Cintsa and drowned ridges form reefs at sea. The greatest extent of aeolianite occurs onshore of the wide continental shelf in the south from which more sand was derived.
North of East London where the continental shelf is narrow, sands were available only close to river mouths and dune development is, therefore, localised. The dunes are thus of various ages as sand was blown onshore each time the sea level fell. The oldest are the inland aeolianite solidified dunes and the youngest are the low fore-dunes on the present beaches.
The gross outline of the present Eastern Cape coast was formed at the time of the break-up of Gondwanaland (an extensive southern super continent composed of Africa, South America, India, Australia and Antarctica) which occurred towards the end of the Karoo period in Jurassic time, caused faulting, uplift and volcanic outpourings and resulted in intrusion of dykes and sills of dolerite.
Much later, Pleistocene Northern Hemisphere glaciations caused sea level fluctuations, which affected the Eastern Cape coast. During the glacial low sea levels, calcareous sands blew onshore and were deposited against any uneven ground. These dunes have been hardened by lime cementation to form aeolianite ridges that exhibit marked cross bedding confirming their dune origin.
HOW THE FOOT PRINTS WERE FORMED AND EXPOSED
The footprints were left in damp sand and afterwards dry sand would have been blown in by the prevailing westerly wind. Over thousands of years, many extra layers of sand built up, and eventually by pressure, the lower layers turned to sandstone.
Coastal winds blow sand and shell fragments that build up to form dunes. Since the direction and strength of the wind varies, the sand is deposited in the form of thin layers that follow the angle of the dune as it builds up or is eroded. Each new layer is different, eg finer / coarser sand grain size, drier / wetter surface, thinner / thicker, etc. Surface details, such as ripples and tracks, may be filled and covered by subsequent layers of sand which preserve their original form. Over time rain and ground water dissolve the shell fragments in the dune. This releases calcium carbonate, which crystallizes and cements the sand grains to form a hard rock dune.
As the sea level was rising at that time, wave action eventually eroded the edge of the dune which had formed over the rock containing the footprints, and scooped out the lower layers, leaving a shallow cave. Erosion later caused the dune rock to break in slabs along the old surface planes, which are weak joints. These slabs fell off and exposed the old surfaces and features preserved on them, notably the footprints.
THE PRINTS ON DISPLAY
The prints which the East London Museum has on display are positive casts of the upper layer (A) of dune rock. These prints were exposed and remained visible when the layer of dune fell. The lower layer (B) of dune rock would have contained the original tracks left by the person. Unfortunately these were not preserved.
DATING - HOW OLD ARE THESE FOOTPRINTS?
The footprints themselves cannot be dated. Scientists dated the sand layer in which they were made and those above and below. Two types of Luminescence dating and Uranium Series dating methods were used. Scientists discovered that the quality of electrons (radioactivity) that attach themselves to quartz and feldspar sand grains increases with time as long as they are not exposed to light. This is after sunlight “zeroed” the clock before the prints were covered in sand. By counting the quality of electrons trapped on the sampled sand grains, the time when the grains were buried can be calculated (Luminescence dating). Sunlight causes electrons to be removed from the sand grains so samples for dating are collected in aluminium tubes to protect them until dating specialists can analyse them under special laboratory conditions. In Uranium-series dating the rates of decay of various uranium isotopes are known and the remaining amounts are calculated to obtain dates. From the results and by comparison with the slope of the dune and an estimate of the then current sea level, the footprints have been dated at approximately 200 000 years.
Geologists and sedimentologists use such layers and details about the surface of the sand grains in them to identify the origin of rocks and to study their structure.
WHO WAS THE FOOTPRINT MAKER?
Not much is known about the life-style of southern African humans of 200 000 years ago. The stone toolkit used by humans at the time that the Nahoon footprints were made is on display in the museum. The artefacts came from beach rock at Nahoon and are of similar age to overlying calcified dunes bearing the human imprints. The tools are typical of the Middle Stone Age, which ranges in age from 250 000 to 30 000 years BP and comprises, knives and points.
Middle Stone Age people were essentially hunter-gatherers, but also consumed large quantities of shellfish in the coastal areas, an important source of protein. Although physically very like modern humans, culturally they were probably quite different.
RECENT FINDS OF FOSSIL FOOTPRINTS IN NAHOON NATURE RESERVE
About seven years ago a huge rock which was part of the roof of the well-known Bat Cave near Nahoon Point fell down, again luckily in one piece. It took ten men to lift and carry the huge rock which was then taken back to the lab. There are still traces of fossil footprints in the roof of bats cave, but it is too high to be readily investigated at this stage. But the rock pieces at the lab are being investigated using the very latest techniques that can scan the interior of the rock in 3D.
If you would like to visit the cave then this cache will give you more information: GC2KTX2 NPNR Trail (8) Bats Cave
Did you know?
Trace fossils are geological records of biological activity, like footprints, and people who study them are called ichnologists.
References:
http://elmuseumscience.wordpress.com/2012/05/16/trace-fossil-footprint-talk-comment-from-u3a-newsletter/
East London Museum display
A Field Guide to the Eastern Cape Coast RA Lubke, FW Gess & MN Bruton