11.   They are mostly men with lines circling their faces like tree trunk rings.

12.   Tree rings, layers of ancient pollen, and cores from icecaps and sea floors also testify to environmental changes.

13.   Tree rings show that pine forests have a fire every few years.

14.   Tusks, Fisher says, grow in layers like tree rings.

15.   Until now, most Midwestern tree ring specialists only looked back two or three centuries by taking core samples from living trees or logs used in construction.

16.   Overpeck said summertime temperatures leave distinctive marks in lake sediments and tree rings and that ice cores capture atmospheric gases.

17.   Coral, ice corings, tree rings and flood deposits have suggested that the weather phenomenon is much more ancient, although the evidence was always isolated or disconnected.

18.   Measurements of the iceberg drift and the tree rings showed a similar cycle, Bond said.

19.   Since then, Oren said, growth in the tree rings fumigated with extra carbon dioxide slowed to about the same rate as the control trees.

20.   Scientists hope tree rings will tell.