scientists today are trying to determine the full effects and causes of ongoing
climate change, it's not the first time the earth has experienced such
changes. For example, in what is now
Botswana's Kalahari Desert, a giant dry lake bed is revealing clues to ancient
weather and how early man adapted.
Oxford University Professor David Thomas says Lake
Makgadikgadi was big – very big.
Something he calls a mega-lake.
its largest extent, a lake that was 60,000 square kilometers in area…about the
same size as Lake Victoria. So, it's a
pretty big lake, varying in depth, but many tens of meters deep. And a lake that clearly is the size of a
small inland sea. So in windy conditions
you'd have stormy conditions on it," he says.
lake grew, shrank, disappeared and grew again over the last 250,000 years
depending on the climate and rainfall.
and his colleague Sallie Burrough say the lake bed is revealing how people
there lived, especially in the Middle Stone Age – beginning about 110,000 years
ago and ending some 50,000 years ago.
Middle Stone Age is when us, as in our anatomically modern humans,
evolved. So this isn't about some deep
ancestor. This is our direct ancestors
and how they used this environment," he says.
Tools for the taking
the lake bed, they found tens of thousands of small stone tools and some very
have here a small number of giant hand axes.
They're 12 inches long (30.5 Centimeters). And they're very heavy as well. They're very unusual. They're probably the
Giant stone axes found on ancient lake bed floor in Botswana
largest axes ever found,"
how those axes were used is a mystery.
One possibility is that they were used as raw material from which
smaller tools were made. Or maybe they were just symbolic.
to do with fertility or even it's been suggested something like a shop
sign. Another alternative is they're
practice pieces – the sort of things you showed people to teach them how to
make a stone tool. So they're very, very
debatable and contentious in terms of what they mean," he says.
since the ancient axes are heavy, it's unlikely they'd be carried by hunters in
pursuit of their prey.
what's also significant is that the axes and many tools were found on the lake floor,
not along what would have been the shoreline.
it really means is that the lake was very, very important to people, not so
much when it was a big, permanent lake, but when it had seasonal water in it,"
Why is that important?
have a lake basin that seasonally has water in it, which is the case today, it
becomes a very important location because of course animals going to where
water was available," he says.
Stone tools are tens of thousands of years old
animals would concentrate around watering holes when the lake was low. So, as the climate changed, so did hunting
were opportunistic. They were using the
environment, taking the resources that were available and moving according to
where those resources were," says Thomas.
more, when Lake Makgadikgadi was a mega-lake, it may have been used as part of
the route humans took to exodus Africa for Europe and elsewhere. That's a possibility being studied.
political boundaries and the huge increase in population prevent such mass
migrations from happening again.
researchers are also studying the tools to determine where the people traveling
Oxford Professor David Thomas says early humans adapted to giant lake's rise and fall
through the lake region came from. How the tools were made could indicate whether
they came from the tropical parts of the continent or from what is now South
if the lake has appeared and disappeared many times over the course of 250,000
years, could it come back yet again?
could come back for two reasons. One is if you have more rain in the catchment
area that would feed the rivers that would drain into the basin. But the other thing is, once you start to get
a big lake it actually starts to affect its own regional climate. Because you've got a big body of water that
when it's warm can supply moisture to the atmosphere. And then it becomes s self-feeding
system. So, yeah, it certainly could
come back," he says.
research is also set for next year to determine if the lake basin was once
linked to the Zambezi River.
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