Biologists build on models from geologists who build on models from planetologists. But what if the bottom model is false?
Scientists use models to try to understand the unobservable past. As an example, this paper in Icarus tries to understand the history of the moon by looking at craters we see today. The researchers plug in values for thermal conduction and convection based on calculated values for impact heat and composition of the ejecta. They conclude that thermal anomalies for long-ago huge impacts can remain to the present day, and that “Impact bombardment may alter lunar contraction history.”
Theories of lunar contraction, however, rely on other models, plugging in the properties of lunar materials and assumptions about the moon’s origin and the constitution of its core. How much of this is reliable? Scientists attempt to compare model predictions with present-day observations, but it’s a two way street. Notice that the abstract concludes, “model-predicted present-day thermal profiles match independent constraints better if the bulk Moon is not significantly enriched in refractory elements compared to Earth.” There’s an “if” in there. If the model predictions don’t fit the observations, scientists can tweak them till they do. But that opens the model to charges of ad hoc reasoning. Unreliable models built on unreliable models can be likened to a house of cards.
A popular model employs patterns of crater formation to explain everything from climate change to extinction. According to this model, an unseen nearby star with a very long elliptical orbit periodically sends debris toward the Earth. If this were true, extinctions from large impacts should date to somewhat regular intervals. Some secular geologists found this idea so attractive, they even gave the mysterious star a name: “Nemesis.” But now, a European scientist looked again at the crater data and found no pattern at all. Science Daily says,
Do mass extinctions, like the fall of the dinosaurs, and the formation of large impact craters on Earth occur together at regular intervals? “This question has been under discussion for more than thirty years now,” says Matthias Meier from ETH Zurich’s Institute of Geochemistry and Petrology. As late as 2015, US researchers indicated that impact craters were formed on Earth around every 26 million years. “We have determined, however, that asteroids don’t hit the Earth at periodic intervals,” says Meier, refuting the popular hypothesis.
In the past, researchers have even postulated the existence of a companion star to the Sun. This supposed dim dwarf star, named Nemesis after the Greek goddess of revenge, was believed to draw near to the Sun every 26 million years and cause asteroids to bombard Earth. This would next occur in around 10 million years. Nemesis, however, has never been found.
So if you continue to see stories about Nemesis causing extinctions on the Earth, you will know that it has no basis. Even scientists can promulgate fake news.
What’s the likelihood that stories of Nemesis will continue in the cultural mythology of science writers for decades to come? There’s another fake-news meme connected to it that has also been undermined: the so-called “Late Heavy Bombardment.” Add these to other myths like Snowball Earth, The Great Oxygenation Event, and others.