Just as a lark and as a little exercise in making HTML tables (and to make clear what one error was in that last post), I threw together this table of the geological time scale, taken from Mayr’s What Evolution Is. I come from that generation of biologists where we were required to memorize the timescale to this level of detail; I’m a bit rusty on the dates now (but these are pretty much the same as what I had to learn in the late 1970s), and I was just realizing that we don’t even mention this stuff in introductory biology anymore.
|The Geological Timescale|
|Mesozoic||Cretaceous||Late||Extinction of dinosaurs|
|99.6||First placental mammals|
|Carboniferous||Pennsylvanian||first mammal-like reptiles|
first land plants
|Silurian||first jawed fish|
|542||first shelled organisms|
|Proterozoic||first multicellular organisms|
|Hadean||origin of life?
|4650||formation of the Earth|
|(from Mayr, What Evolution Is, 2001)
(revised to dates at Overview of Global Boundary Stratotype Sections and Points
Here’s something that I also find peculiarly interesting. One of the older textbooks I’ve got in my little office collection is an introductory biology text from 1939; take a look at the dates students had to learn then.
|The Geological Timescale
|(from Walter, Biology of the Vertebrates, 1939)|
There was a big change in our understanding of the age of the earth within my parents’ lifetimes. I trust it’s obvious what happened: nuclear physics and radiometric dating.