Cosmology: snowball Earth from methane drop (Introduction)

by David Turell , Saturday, April 06, 2024, 17:27 (230 days ago) @ David Turell

Less methane, more cold with less greenhouse gas:

https://bigthink.com/starts-with-a-bang/oxygen-killed-life-on-earth/?utm_source=interna...

"The cyanobacteria, experiencing the massive success of having an unlimited nutrient source wherever sunlight strikes the surface of the ocean, evolved into microbial mats in short order. Once they began producing oxygen, the early presence of that molecule systematically removed the early methane from Earth’s atmosphere, as oxygen reacts with methane to produce carbon dioxide and water. The loss of that early methane — a fabulously efficient heat-trapping molecule — greatly decreased the greenhouse effect from Earth’s early atmosphere: causing global temperatures to begin to drop.

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"The Sun’s energy output, like that of all stars, was much lower in the early stages of its life, and so the large abundance of atmospheric methane was the only thing keeping Earth warm enough to have liquid water on its surface. With the oxygen destroying that powerful greenhouse gas, the planet couldn’t retain its heat nearly as well. This spawned the greatest ice age in history, leading to Snowball Earth conditions that lasted for approximately 300 million years.

"The geological evidence is overwhelming for incredibly cold conditions covering the entire planet at this time. Glacial deposits throughout northern North America (but also found as far away as Australia) display multiple sedimentary layers that show evidence for this frozen period persisting for long periods of time, spanning ages that correspond to being between 2.5 and 2.0 billion years ago. Evidence for past glaciation events, where glacial deposits must have been made even at then-tropical (i.e., equatorial) latitudes, has been very strong for more than half a century.

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"Once you cool the Earth and remove its heat-trapping atmospheric layers, further cooling appears to be a runaway process. If ice sheets advance far enough down below the polar regions, it increases the total reflectivity of the planet, which translates into less solar energy being absorbed by the Earth overall. The further cooling leads to the formation of even more ice, which can eventually cover the entire surface of the planet — continents and oceans both included — in a global layer of ice. That’s what a “Snowball Earth” set of conditions looks like.

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"It was geology, however, and not biology, that eventually led to the end of these Snowball Earth conditions. Even as the planet remained frozen, plate tectonics continued, as continental drift, seafloor spreading, earthquakes, and volcanic eruptions all persisted. In particular, volcanoes continued to erupt beneath the ice, spewing those volcanic gases upward, where they would lead to cracks and fissures in the ice sheets. As volcanoes add copious amounts of carbon dioxide to the atmosphere, they began increasing the strength of the planet’s greenhouse effect once again, while the simultaneous production of ash began to decrease the reflectivity of Earth. Eventually, after approximately 300 million years, our planet finally broke out of this glaciation era.

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"Although much remains to be learned about the evolutionary process during these Snowball Earth conditions, it’s arguable that human-like life would never have arisen if oxygen had never destroyed our methane-rich atmosphere and given life the opportunity to evolve in this spectacular, unique direction.

"The period of time corresponding to 2.5 billion years ago in Earth’s natural history may yet represent the greatest mass extinction our planet has ever faced. Even at this primitive stage, however, life remained ubiquitous and resilient, with the destruction of the pre-existing dominant species enabling other, new organisms to evolve and rise to prominence, filling those now-vacant ecological niches. The Great Oxygenation Event was a transformative occurrence in Earth’s history, and may have paved the way for complex and differentiated life on our world. Without it, life may never have achieved the diversity it now boasts today, and the tree of life may not have been capable of giving rise to intelligent, advanced organisms like us."

Comment: this description of the history and causes of snowball Earth presents us with an amazing set of improbable contingencies which allowed us to appear. The logical explanation is a designer God.