It might seem like geologists are just studying a bunch of old – and sometimes really old – rocks. The reality is that Earth science researchers look back at the geologic record of our planet to understand how we got here, and what we can expect next for life on Earth.
In a study, to be published in Geoscience Frontiers in November 2021, researchers from New York and California helped pinpoint an important fact about our planet that has huge implications for us: the Earth has a "pulse," or regular peaks of geologic activity. They identified the pulse in part by looking at mass extinctions, something we obviously want to know about since this is the only planet our species currently calls home.
Taking Earth's Pulse
The results of this study are actually not new – they're just a more specific measurement that tries to answer a question researchers have been asking for nearly a century. In this new study, the researchers used the latest technology to analyze 89 geologic events in the past 260 million years of Earth's history, employing a statistical technique called Fourier analysis to determine if there was any pattern in the frequency and consistency of the data.
When all the numbers were crunched, it turns out there is a pattern, and it falls exactly within the range proposed by previous researchers. Across those 89 events – which the authors wrote included "marine and non-marine extinctions, ocean-anoxic events, sea-level oscillations, continental flood-basalt eruptions, [and] pulses of intra-plate magmatism," they found 10 clusters of data. These geological events occurred roughly every 27.5 million years.
Past research suggested that each of Earth's pulses was between 26.4 and 30 million years apart; this study narrows that down further.
The Causes are Still Unknown
While it's certainly fascinating to have another data point suggesting there is a consistent rhythm to cycles of activity – and life – on Earth, the researchers in this study are not much closer to understanding why Earth has a pulse.
The authors of the study do propose some ideas though. One suggests that internal forces within and on Earth (magma activity, tectonic activity, and climate change) may explain the cyclical pattern. Other ideas point to consistent changes in our planet's orbital cycles, and the fact that our solar system also has a cyclical movement within the Milky Way galaxy roughly every 30 million years.
No matter the cause, this study suggests that the data is conclusive: every 27.5 million years, we can expect an uptick in geologic activity which often results in mass extinction.
The Next One is Coming Eventually
Never fear though, as 27.5 million years is a very long time for humankind. On the scale of planetary history, this time frame is brief, but homo sapiens is believed to be just about 200,000 years old as a species – that's less than 1 percent of each pulse.
And we're between pulses right now: the study suggests that the next pulse will be roughly 20 million years in the future. For context, while dinosaurs went extinct roughly 65 million years ago, commonly recognized modern animals like bears, crows, and whales were only just emerging on the evolutionary timeline 20 million years ago.