Friday, December 24, 2010

CONTINENTAL SHEILDS

CONTINENTAL SHEILDS

The centres of the earth's continents ,known as sheilds ,were established between 2500 and 500 millions years ago ,some certain rocks over three billion years old . They were formed by a series of turbulent events ,plate movements , earthquakes ,and volcanic eruptions . Since the pre-cambrian period ,over 570 million year ago ,they have experienced little tectonic activity ,and today ,these flat ,low-lying slabs of solidified molten rock from the stable centres of the continents . They are bounded or covered by successive belts of younger sedimentary rock.

No comments:

Post a Comment