Annamaria on Monday
To geologists, the most interesting place is in
East Africa: the largest seismically active rift system on earth. What’s happening there is that new tectonic
plates are being formed by their spreading apart from the landmass. This the opposite of where tectonic plates
have pushed into each other to form mountain ranges. In this case, when hunks of a tectonic plate
separate, it causes chasms. In the
distant past, other such divorces have taken place on our sacred planet, but
they are all now underwater or silted in—no longer active.
The separations—and there are two of them—taking place in
East Africa have been going on since the onset of the Miocene about 25 million
years ago. The Nubian Plate and the
Somali Plate are still moving, now at the rate of six or seven millimeters per
year. In another 10 million years or so,
the Somali Plate will be completely broken off, and the sea will surround it.
Earth scientists are fascinated to be able to study this
process and to theorize about why and how it is happening in this geologic
wonder of the world. The rift area includes not only parts of
Ethiopia and Somalia, but also extends into Kenya, Uganda, Tanzania, and the
African Great Lakes. The rift is deepest
north of Nairobi. Theories vary as to
why this process is underway just there and no where else on earth. It seems that, like many thorny scientific
questions, this one is a result of interactions of more than one force, making
it difficult to sort out.
We know that the East African Rift Zone is the site of many
dormant and active volcanoes, fifty of them in Ethiopia alone. The Crater Highlands of Tanzania are part of
this system, even though they now lie outside the rift area. One of the active volcanoes is unique: The
magma of the Ol Doinyo Lengai volcano contains no silica, so it has extremely
low viscosity. National Geographic
described it this way: “Its lava fountains crystallize in midair then shatter
like glass.” Wow, wouldn’t I love to
witness that!
 |
| Ol Doinyo Lengai |
Most fascinating to me is that this is where our race Homo Sapiens evolved. The bones of our hominid ancestors have
emerged from the sediments of the Rift Valley highlands. These include the famous “Lucy”, the partial australopithecine
skeleton from 3 million years ago, discovered by anthropologist Donald
Johanson. The rift in Ethiopia more
recently yielded two other 10-million-year-old hominid ancestors: Chororapithecus abyssinicus and Nakalipithecus nakayamai.
Since so many hominid fossils have been found in the Great
Rift Valley, scientists have begun to think that the evolving conditions there
played a pivotal role in the development of our species. Current theorists believe that the local
situation caused the climate to alternate between wet and arid, which forced
our hominid ancestors to adapt by becoming bipedal, increasing their brain
power, and developing culturally. My
favorite article on this theory is the 2008 paper by Beth Christensen and Mark
Maslin, delightfully titled “Rocking the Cradle of Humanity.”
For me personally, the African wilderness plays in my blood
and in my soul in such a way that my response runs far deeper than ordinary
joy. This is where our species evolved, and I
believe that, when we human beings go there, regardless of where we were born,
on a cellular level, we recognize the place as home. Ever since I first went, when I am not there,
in my soul, I am homesick for it.
