Declan -
You may already be aware of this, but did you know that you can include a timestamp in the KML description?

You can then select the placemarks using the 'time' gui in the tools menu. I believe that the feature is only availble in the EC version of Google Earth, but it's quite useful.



Here is an example of the kml:

Code:

---

    <Placemark>
      <name>SATURN</name>
      <TimePeriod>
        <begin>
          <TimeInstant>
            <timePosition>1957-08-10</timePosition>
          </TimeInstant>
        </begin>
      </TimePeriod>
      <styleUrl>#khStyle563</styleUrl>
      <Point>
        <extrude>1</extrude>
        <altitudeMode>relativeToGround</altitudeMode>
        <coordinates>-116.02,37.1138,0</coordinates>
      </Point>
    </Placemark>

---

You can find an example of a time series here: Nuclear Tests