Clearwater Lakes: Shape, Impact and Age

Make the original proposal explicit

Innes and Beals discussed the two Clearwater Lake basins and proposed impacts from a related pair of objects. The proposition has two parts. One concerns the origin of each basin. The other concerns the relationship between their dates. An aerial shape and the proximity of the lakes were useful clues for deciding what to investigate.

Library and Archives Canada describes a broader programme that paired aerial photographs with field investigation. Read the image as a search tool. The shape of a lake does not in itself date its formation or identify the process responsible for it.

Sources for this section: [1] · [2]

Read a later test of timing

Schmieder and colleagues reported argon dating from impact melt material from both structures. The results supported separate ages rather than a single event. That comparison can revise the shared-event proposal while leaving the evidence for impact origins in place. A later measurement can reject one part of a historical explanation without discarding the observation that prompted it.

The distinction also explains why the basins should be described using the estimates from the work actually cited. Later research can revise geometry as well as timing.

Sources for this section: [2] · [3]

Try a two-site evidence log

Imagine two circular sites with rocks consistent with impact and independent age ranges that do not overlap. Record the evidence for origin in one column and the evidence for simultaneity in another. The origin may be supported at both sites while the shared date is not. If the age ranges overlap instead, the dates would be consistent with a shared event, but overlap alone would still be weaker than a demonstrated connection.