studies, however, failed to link unequivocally terrestrial(30)

 

climate and the solar-activity cycle, or even to contirm

 

the cycle’s past existenue.

 

If consistPn! and re!iab!e geo!sgigal~-arek-xologieal

 

evidence tracing the solar-activity cycle in the distant

 

past could be found, it might also resolve an important(35)

 

issue in solar physics: how to model solar activity. Cur-

 

rently, chere are two models of solar activity. The tirst

 

supposes that the Sun’s internal motions (caused by

 

rotation and convection) interact with its large-scale

 

magnetic field to produce a dynamo. a device in which(40)

 

mechanical energy is converted into the energy of a mag-

 

netic field. ln short. the Sun’s large-scale magnetic field

 

is taken to be self-sustaining, so that the solar-activity

 

cycle it drives would be maintained with little overall

 

changc for perhaps billions of years. The alternative(45)

 

exp)anarion supposes that the Sun’s large-sca)e magnetic

 

field is a remnant of the field the Sun acquired when it

 

formed, and is not sustained against decay. In this

 

model. the solar mechanism dependent on the Sun’s

 

magnetiC field runs down more quickly. Thus, the char-(50)

 

acteristics of the solar-activity cycle uvuld be expected to

 

change over a long period of time. Modern solar obser-

 

vations span too short a time to reveal whether present

 

cyclical solar aCtivity is a long-lived feature of the Sun,

 

or merely a transient phenomenon.