African Fossils
africanfossils.org
africanfossils.org
When reading about some piece of science I often wish I could gauge how certain science is about something and why. Human evolution is always going to be a fascinating topic. It's got a lot of uncertainties, contradictory theories and less-than-certain facts that make it into pop science.
Do we have hundreds of high quality fossils for some homo species or is it just a few skull fragments? It's great to be able to interact with evidence/finds like this directly.
I often wonder in a similar direction. For example, this headline from a few days ago:
"Horrific FLESH-EATING PLATYPUS once terrorised Australia"
...based on finding a single tooth, it seems.
http://www.theregister.co.uk/2013/11/05/new_platypus_species...
The ages are based on the stratigraphy that the fossils are in. We can "easily" correlate stratigraphy across wide areas, but most sedimentary rocks are hard to date. For these particular fossils, the stratigraphy happens to contain a lot of volcanic ash units that can be directly dated. In most cases, we use the fossils present (biostratigraphy) to correlate with other units that can be directly dated.
The exact numerical age is based on dating things like feldspar grains in volcanic units that can be dated with K/Ar dating or zircons in volcanics that can be dated with U/Pb, etc, etc.