WHAT HAPPENED 65 MILLION YEARS AGO?
Ask someone how the dinosaurs died, and chances are they will tell you about an apocalyptically bad day 66 million years ago, when a huge asteroid slammed into Earth and triggered a nuclear winter. This event left behind distinct traces in the geologic record, as well as a vast crater off Mexico’s Yucatán peninsula called Chicxulub. But since the 1980s, researchers have debated whether volcanoes in ancient India may have been an accessory to the mass extinction — or even its main driver… According to the two teams, the massive volcanoes, called the Deccan Traps, started erupting about 400,000 years before the Chicxulub impact and wrapped up about 600,000 years after the end of the Cretaceous period. At least half of the volcanoes’ total erupted lava spilled out after the impact… The eruptions could have injected massive amounts of greenhouse gases and particles into the atmosphere, changing Earth’s climate in ways that stressed out late Cretaceous life. Then, in a one-two punch, the impact’s nuclear winter would have sharply cooled Earth and caused ecosystems to collapse.
After such a good explanation would be strange to ask “But why that happened and why 65 million years ago?” This strange question has a very precise answer that brings some adjustments to the explanation above. Let’s start from the Wikipedia’s map of Milky Way and our Solar system in it:
Actually, it is incorrect that our Sun has a circular orbit in the galaxy. We have learned that stars lose velocity when they enter an arm and gain velocity on exiting an arm. Let me try plotting approximate Sun latest orbit with the red line below, near the yellow circle that is a good approximation for the latest 65M years:
Sun circular orbit is estimated to have 225M-250M years period (https://earthsky.org/astronomy-essentials/milky-way-rotation/#). We go with more than 250M estimate, considering that real orbit is actually longer than the circular. That gives us a point when Sun left Scutum-Centaurus arm (either by the yellow circular orbit or by the red combination of elliptic orbits) approximately 65M years ago on the map above.
Let’s see how leaving an arm can cause tectonic and volcanic activities and asteroid events on Earth, and the decline in Solar activity.
When Solar system left the arm, it entered slower time zone. (Check details in SPIRAL GALAXIES AND no-no DARK MATTER). Fusion processes and Solar activity slowed down because Hydrogen atoms slowed down their run. Despite fusion (in Sun) and fission (in Earth) chain reactions slowing down due to the time dilation for atom or neutron runs, there is no impact on radioactive decay for a single atom, because internal time of an atom is not impacted.
There are estimates that half of contribution to the Earth tectonic and volcanic activities come from the decay of radiogenic atoms in the Earth:
https://www.nature.com/articles/srep37740.pdf: “The KamLAND Collaboration reported that heat from radioactive decay of radiogenic isotopes such as 238U and 232Th contributes about half, 21 TW, of Earth’s total heat flux (44.2±1.0 TW) and that Earth’s primordial heat supply has not yet been exhausted.”
https://blogs.scientificamerican.com/observations/nuclear-fission-confirmed-as-source-of-more-than-half-of-earths-heat/#: “Earth is chock full of such radioactive elements — primarily uranium, thorium and potassium. Over the billions of years of Earth’s existence, the radioactive isotopes have been splitting, releasing energy … That energy heats the surrounding rock and keeps the elemental forces of plate tectonics in motion.”
- Now imagine what happens when time on Earth slows down, but the energy flow from radioactive elements decay stays same. Dissipation of this energy slows down because of tie slowing down.
- Or, if “time on Earth slowing down” is hard to imagine, then let’s imagine relatively the same scenario — time on Earth stays same, but energy flow from radioactive decay increases.
- Either way it leads to Earth crust heating up and to tectonic and volcanic eruptions.
That explains how CO₂ production increased (due to the volcanic activities) and how photosynthesis by plants consuming CO₂ and producing oxygen decreased (due to the Solar activity decline by time slowing down there). That was the leading cause for big animals’ extinction.
Asteroids did not help either. Why asteroids are more likely to collide with Earth on exiting or entering a spiral arm? We discussed a similar question in the chapter about spiral galaxies: objects’ trajectories change on entering or exiting an arm. Stars rotating in the same plane avoid collisions by repelling each other by same polarity magnetic fields. But Earth has no such protection: its magnetic field is not that strong and asteroids have none.
If you liked this story, check Life Hacked Time as well.
