Changes in the intervals between ice ages at 2.8 million and
1 million years ago, as documented by deMenocal, coincided with the times at which African antelopes and related creatures evolved into the greatest diversity of species, Vrba says.
Following that 1969 high, there was only one year that malleable iron shipments surpassed the 1 million ton level.
It wasn't until 1983 that steel casting shipments slipped below the 1 million ton level.
Since that time, steel foundries again demonstrated their resiliency by topping the 1 million ton mark by 1988.