As experiences from Greenland and Australia illustrate, it is difficult to find readable records here on earth because the constant motion of tectonic plates have so chewed them up over the past four billion years.

• 格陵兰与澳洲的经验告诉我们，在地球上很难找到可资辨认的记录，因为地壳板块不断运动，已经把这些记录吞吐了40亿年。