It covers roughly the period known as the Middle Stone Age (MSA).
This coverage gap lies beyond what is considered the effective range for radiocarbon and prior to what is considered the effective range for potassium-argon.
This problem period may be even larger because: (1) some dating authorities believe that the effective range for K-Ar doesn't begin until about 400,000 ya, and (2) many of the older fossils are found at sites that lack the volcanic rocks necessary for K-Ar dating and hence cannot be dated by this method at all.
Although young-earth creationists challenge the legitimacy of all of the dates obtained by the long-term radiometric methods, even evolutionists are beginning to admit that this dating gap presents a problem for them.
However, because of severe dating problems which are seldom mentioned, this alleged sequence cannot be maintained.
To present the fossil evidence as a relatively smooth transition leading to modern humans is akin to intellectual dishonesty.
Evolution places severe demands upon fossils used to support it.
This gap is from about 40,000 ya (years ago) to about 200,000 ya on the evolutionist's time scale.
Popular presentations of human evolution show a rather smooth transition of fossils leading to modern humans.
The impression given is that the dating of the individual fossils in that sequence is accurate enough to establish human evolution as a fact.
However, the real seriousness of this problem seems to elude them, even when they occasionally refer to it in their writings. In the past 15 years, the major focus of human evolution has shifted from the origin of "all" humans to the origin of "modern" humans, and the very time during which modern humans are alleged to have evolved from their more primitive human ancestors is the period covered by this gap.
Since the morphology of a fossil cannot be changed, it is obvious that the dating is the more subjective element of the two items.Yet, accurate dating of fossils is so essential that the scientific respectability of evolution is contingent upon fossils having appropriate dates.