-The discovery-
In 1976
Mary Leakey, accompanied by her husband
Louis Leakey, led a
research team to
Olduvai Gorge to study and hunt for
hominid fossils. Along the way they decided to stop just south of their destination. It was here that an important
discovery in
human evolution took place.
Credit generally goes to Mary Leakey and her husband for the find; they were the
anthropologists leading the team and certainly the most widely known. However, it was
paleoanthropologist Andrew Hill who stumbled upon a 3.6 million-year-old trail of
footprints while tossing
elephant dung at a colleague.
Mary took samples from, and made molds of, the seventy footprints that ran in two
parallel lines for thirty meters, then covered the site. This last bit was important to prevent the further
wearing away that had already begun on the exposed prints. Later the
site was
preserved against the elements and encroaching vegetation and any saplings that spring up are removed.
-The prints-
The footprints are an important find because they are "a fossil of
human behavior--
prehistoric walking." They showed that 3.6 million-years-ago our ancesters were
bipedal hominids, something that at the time hadn't been proven.
Scientists can look at the impressions, measure the
depth of them, and deduce that, like
modern man, these hominids walked upright. There are two primary characterizations of the prints that give this away. One is that unlike the foot of a
chimpanzee or
orangutan, the
big toe of this
hominid isn't
diverged from the rest of the foot. Rather, it is set close to the remaining toes much the same as the one in your shoe right now.
The other characteristic can be seen in the
gait of the footprints. When chimpanzees walk on their legs alone, they put their
weight on the outside edges of their feet. A hominid that primarily walks
upright and doesn't spend much (if any) time in the trees, however,
initially puts their weight on the heel then transfers it along the side, across the ball of the foot and
pushes off with the big toe.
-Placing the prints-
That we found such a great
specimen of footprints after millions of years was lucky. It required an excellent set of circumstances to occur. In the case of the
Laetoli footprints this is what we believe happened:
Millions of years ago in what is now known as Laetoli,
Tanzania a volcano erupted. This
volcano, now known as
Sadiman, sent great clouds of
ash into the air. The ash coated the earth in a fine
layer as the inhabitants of the area fled for safety. Among the animals and birds that scampered in the
sand were two
Australopithecus afarensis travellers. Since one set of footprints is slightly smaller than the other it is believed that it was a
male and
female who transversed Laetoli. This couple, possibly followed or accompanied by a smaller hominid, stepped in the ash as it began to rain lightly. Their feet
sank into the moist sand leaving impressions. The volcano erupted a cloud of ash again and sealed the footprints, drying in a
cement-like way and preserving them for later discovery.
References:
Human Ancestors Hall, http://www.mnh.si.edu/anthro/humanorigins/ha/laetoli.htm
Laetoli: Footprints in the Past, http://emuseum.mnsu.edu/archaeology/sites/africa/laetoli2.html
PBS: A Science Odyssey, http://www.pbs.org/wgbh/aso/tryit/evolution/footprints.html
PBS: Evolution, http://www.pbs.org/wgbh/evolution/library/07/1/1_071_03.html