“On these timescales, we’re not really good at fine-tuning an age for the exact missing time,” says Francis Macdonald, professor of geology at the University of California at Santa Barbara, who was also involved in the research. “And so the previous theory suggested that okay, it all forms once, with glaciation – but we say ‘no, it formed over hundreds of millions of years’… when you get better data, they [the unconformities] are not exactly correlative. “
If the two sets of erased rocks are truly independent of each other, it suggests that they were not caused by some extraordinary event like snowballing earth after all. In this case, Flowers suggests that they may have been formed by tectonic processes that pushed vast amounts of the earth’s crust upward. There may not have been any erosion either – it is possible that the higher elevation simply made it difficult for sediment to deposit, and therefore little rock formed around this time in the first place.
An unsolved mystery
It’s not quite the end, however. The debate continues – every expert I have spoken to has stressed the need for more data. And luckily, it should happen.
” I think there is [been] renewed interest [in this geological enigma]Macdonald explains. Ten years ago, there was relatively little research into the Great Discordance and its causes. But a wave of new wacky theories – and the emergence of technologies capable of testing them – has transformed the field.
A game-changing technique known as thermochronology involves extrapolating the history of rocks by measuring how their temperature has changed since their formation.
“So for example [with older methods], if someone says it dated a granite and is 100 million years old, it is usually referring to when it cooled from magma to solid, ”says Marshak. With thermochronology, you don’t look at when the rock formed, but roughly when it was pushed to the surface of the Earth – and that can tell you a lot about what was going on in the earth. deep past of our planet.
“This technique essentially gave us a window to extract the missing time records,” says Macdonald. Who knows what secrets they might reveal.
Zaria Gorvett is a senior reporter for BBC Future and tweets @ZariaGorvett
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