Evolutionary biologists and geologists speak of events happening millions or billions ago as concrete facts.  They are not observational facts, though; they are inferences from indirect evidence.  Indirect evidence can often lead to different conclusions; in fact, some philosophers like Duhem and Quine argue for “under-determination of theory by data,” meaning that data can never converge to support just one theory.  Some can demonstrate logically that there are an infinite number of theories that can explain a set of data.  Evolutionary scientists counter that there are only one or a few that are reasonable (implying that theirs is among the limited set of reasonable ones).  Recent discoveries that threaten to overturn past reasonable theories, though, cast doubt on their confidence.

Was there a Late Heavy Bombardment?  You can give a prehistoric event a name – even an acronym, like LHB – and it begins to take on a life of its own.  Papers and articles on earth history routinely refer to a “Late Heavy Bombardment” of the inner solar system by large impactors some 3.8 billion years ago, long after the planets are thought to have formed.  Where did that idea come from?  Did it really happen?

The LHB was an inference from radiometric dating of Apollo rock samples from the moon.  Two basins, one thought to be the oldest (Imbrium) and another thought to be the youngest (Serenitatis) turned out to be relatively close in radiometric age.  Scientists “invented” the LHB theory to try to account for the surprising data.  Now, however, Astrobiology Magazine and PhysOrg are saying the LHB never happened.  New evidence from the Lunar Reconnaissance Orbiter has undercut the thinking on which it was based.

When did ichthyosaurs go extinct?  Consensus thinking about marine reptiles named ichthyosaurs (fish-lizards) was that they went extinct at the end of the Jurassic, 145 million years ago.  Now, according to PhysOrg, evidence suggests they did just fine, continuing to thrive and diversify, for another 50 million years.  According to the article, a new paper by European scientists “considerably changes our understanding of the evolution and the extinction of these dinosaur age sea reptiles”.   Notice how drastic the reinterpretation is:

Whilst it had been thought that these Jurassic ichthyosaurs died a little later at the end of the Jurassic, the new discoveries show that in reality almost all of these lines survived across the Jurassic-Cretaceous Boundary…. the team has been able to show that the extinction rates were very low during the Jurassic-Cretaceous Boundary. In fact it seems that the ichthyosaurs were not affected by the Jurassic-Cretaceous Boundary extinction event, contrary to many other groups of marine animals. The reason why the ichthyosaurs did so well during this period in comparison with other groups of marine animals remains a mystery, and will be the subject of future research….

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