I don't know what may have happened 1000 years ago and further but with earthquakes and all like they are now,I think that the gaps are forming because of earth quakes and some are more milder than others. Core of the earth must be getting hotter and hotter. Me and my older brother used to debate on such things as this when we was young.He claimed earth was eventually be the hell of the bible. Others times he would say also that the earth and sun would collide also and cause hell too lol. One never knows for sure.