Indian Ocean

Figure 3.1

Locations of the sites with Oldowan tools, fossils of early Homo, or both mentioned in the text.

the tool-bearing layer accumulated just before 2.5 million years ago. The paleomagnetic method relies on the repeated tendency of Earth's magnetic field to flip 180 degrees, meaning that the direction a compass needle would point has periodically shifted from north to south and back again. Iron particles in volcanic rocks and in fine-grained sediments like those at Gona retain the ancient direction of the field, and the global sequence of shifts has been dated in volcanic rocks (Figure 3.3). Geophysicists use the term "normal" to refer to a time interval when the magnetic field was oriented north as it is today and "reversed" to refer to an interval when it was oriented south. The Gona deposits record a north-to-south shift just below the tool layer, and such a flip is known to have occurred 2.6 million years ago. Together, then, potassium/argon and paleomagnetism bracket the Gona artifacts between 2.6 and 2.5 million years ago.

striking platform

bulb of percussion

striking bulb of platform percussion

core (irregular discoid)

bulb of percussion

core (irregular discoid)

... bulb of s,tnKmg percussion platform r

Was this article helpful?

0 0

Post a comment