Tikalon Blog by Dev Gualtieri

Earth's Pulse

September 6, 2021

Our Solar System is much more serene than it was 4.5 billion years ago. At that time, the Mars-sized planet, Theia, collided with an early Earth to create our present Earth and Moon. This was actually a fortunate occurrence, since much of our water appears to have come from Theia. Still, Earth has experienced a few extinction events caused by meteor impacts in the past several million years, the most famous of which is the extinction of the dinosaurs about 66 million years ago. This was caused by the impact of a 10 kilometer asteroid at the Gulf of Mexico, I wrote about this event in a previous article (The Tanis Deposit, May 6, 2019).

Now that humans have the capability to protect themselves against such catastrophes (see my June 12, 2012, article on the Yarkovsky Effect), we would be remiss not to monitor the skies for threatening asteroids. NASA has created the Center for Near-Earth Object Studies for computation of the orbits of Near-Earth Objects (NEOs) and assessing their impact probabilities in the future.[1] Previously high on the list of possible impactors, but recently downgraded, is the asteroid 99942 Apophis.[1]

The projected 2029 trajectory of the asteroid, 99942 Apophis, which shares its name with the Egyptian deity, Apep, also known by his Greek name, Apophis (Ἄ&pi'οφις). Apep was the greatest enemy of Ra, the Egyptian Sun god, and he was depicted as a giant snake, a probable consequence of his being formed from Ra's umbilical cord. (Left, a still image from a NASA/JPL-Caltech YouTube video showing the calculated orbital trajectory of asteroid 99942 Apophis as it will encounter the Earth on April 13, 2029. The blue dots are geosynchronous satellites, which indicate the nearness of the encounter. Right, a portion of a Wikimedia Commons image depicting Apep held at bay by a deity in the tomb of Pharaoh, Ramses I, circa 1307 BC. Click for larger image.)

After its 2004 discovery, there was a small probability that 99942 Apophis would impact the Earth in 2068. This would be a major problem, since the asteroid is estimated to be about 350 meters in diameter. Recent observations have ruled out any impact risk in 2068 and for many subsequent encounters, but it still approaches Earth closely. On April 13, 2029, Apophis will pass Earth at a distance closer than the distance of geosynchronous satellites (see figure, above).[2]

Impact of large meteors leave a definite imprint in the geological record, but there are other major geological events that lack such a simple explanation. A team of geologists from New York University (New York, New York) and the Carnegie Institution for Science (Stanford, California) have recently published an open access paper in Geoscience Frontiers in which they present evidence that major geological events are cyclic, happening in a 27.5 million year cycle.[3-6] This cycle may be the result of the motion of the Earth in the Solar System and our Milky Way Galaxy.[3]

Says geologist, Michael R. Rampino, team leader for the study and a professor in New York University's Department of Biology, "Many geologists believe that geological events are random over time. But our study provides statistical evidence for a common cycle, suggesting that these geologic events are correlated and not random."[4] The research team examined 89 well-dated major geological events of the last 260 million years. These events include[3-4]

• Marine and land extinctions
• Major volcanic outpourings of lava called continental flood-basalt eruptions
• Major ocean anoxic events (events when oceans were depleted of oxygen)
• Sea levell fluctuations
• Global pulses of intraplate magmatism
• Changes in seafloor spreading rates and tectonic plate reorganizations

The most recent cluster of disastrous geological episodes occurred about 7-10 million years ago; so, the expectation is that we're at least 15 million years away from a series of catastrophic events that might cause human extinction.[6] However, in 15 million years, humans (at least those who inhabit the Earth and not another planet) might be technologically equipped to prevent such a tragedy. A Fourier analysis of the data for these 89 events gives a spectral peak at 27.5 million years at a confidence level greater than 95%. There's also evidence for a significant shorter period of about 9-10 million years.[3]

Left, the results of moving window analysis of the 89 geologic events using a 10-Myr moving window centered every 0.5 Myr. The number of occurrences that fell within the moving window were computed at 1-Myr intervals. Right, Gaussian smoothing of these data with a standard deviation of 5 Myr centered at every 0.1 Myr. (Fig. 1 of ref. 3, licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.[3] Click for larger image.)

This study was enabled by recent improvements in radioisotope dating techniques.[4] Says Rampino, "Back in the early 20th century, no one had very good evidence to show whether they were cycles or not... and many or most geologists thought that these cycles were random."[6] This prevented a quantitative analysis until now.[6] One problem with the analysis is an unavoidable double counting. Since many events are causal, some of the 89 events are related.[5] For example, anoxic events cause marine extinction.[5] A prior study in 2018 found a 26 million year cycle in examination of the Earth's carbon cycle and plate tectonics.[5]

So, what is the likely cause for this periodicity? Two potential candidates are processes relating to plate tectonics and astronomical cycles of the Earth's motion in the Solar System and our Milky Way Galaxy.[3] Also possible are comet strikes and the orbit of the elusive Planet Nine.[5] I wrote about Planet Nine in an earlier article (Planet Nine, June 27, 2016).

The orbit of Planet Nine and other Trans-Neptunian objects. Note, especially, the small size of the orbit of Neptune in this illustration. (Wikimedia Commons image by nagualdesign.)

Earth's Pulse

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