5 ms·

I'm wondering how they end up with numbers like 17 million. Does anybody know?

• steeve 13y ago
  Most likely thanks to Carbon Dating [1] [1] http://en.wikipedia.org/wiki/Radiocarbon_dating http://en.wikipedia.org/wiki/Radiocarbon_dating
  • jofer 13y ago
    No. Carbon dating is only reliable back to ~50ka (50,000 years before present), at most ~100ka. For older things, you're typically dating the formation of a mineral grain. Common methods are Potassium/Argon and Uranium/Lead dating. 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.