Privileged Planet: the faint sun paradox (Introduction)

by David Turell , Friday, January 28, 2022, 23:32 (1031 days ago) @ David Turell

Early sun at 70% of current output makes for frozen Earth. Yet life appeared and survived. Why?:

https://www.quantamagazine.org/the-sun-was-dimmer-when-earth-formed-how-did-life-emerge...

"... If you could travel back in time to the dawn of the solar system 4.5 billion years ago, you’d find a star that was about 30% dimmer than it is now. Over the subsequent eons, it has shone more and more brilliantly — a function of the nuclear fusion process that takes place in the cores of stars like our own.

"That original faint sun should have led to disaster here on Earth. If our modern Earth were placed under that sun, temperatures would average about −7 degrees Celsius — too cold for liquid water to flow. “The planet should have been completely frozen,” said Toby Tyrrell, an earth system scientist. “It shouldn’t have been possible for life to develop.”

"And yet it did. We know that our planet had liquid water on its surface as early as 4.4 billion years ago, and maybe even earlier, as water vapor condensed out of the atmosphere. Single-celled life seems to have sprung up shortly thereafter.

***

"The American astronomers Carl Sagan and George Mullen made a more substantial attempt to resolve the paradox in 1972, performing the first detailed analysis of the faint young sun problem. They suggested that a thicker atmosphere on the early Earth might have been able to trap more heat, keeping the planet warm enough to support liquid water.

***

"Kasting and his colleagues explored carbon dioxide’s possible effects in 1981, noting that volcanoes could have released enough of it to overcome the faint young sun problem. Even if Earth did manage to freeze over — which appears to have happened on at least three occasions — volcanoes poking their noses through the ice might reverse the process. “The resultant large greenhouse effect should melt the ice cover in a geologically short period of time,”

***

"At the dawn of the Hadean, an object at least the size of Mars, and perhaps twice as big, barreled into the young proto-Earth. The collision formed the moon and essentially reset the timeline of our planet to zero. It also likely sent temperatures on Earth soaring, with a vast magma ocean encompassing the planet.

"That magma ocean could have cooled in just a few tens of millions of years, allowing a more recognizable planet to take shape. Evidence for this comes from tiny crystals called zircons.

“'Zircons are the oldest known terrestrial solids on our planet today,” said Dustin Trail, an earth scientist who published work on their properties in 2018. “They have ages that extend back 4.4 billion years.” Studying the ratio of different forms of oxygen in some of these zircons shows that they may have interacted with water as far back as 4.38 billion years ago, pointing to the presence of liquid water and perhaps oceans on our planet almost immediately after the magma ocean phase.

***

" 4.1 billion years ago — some of the first evidence of life appears. In 2015, Elizabeth Bell, a geoscientist at the University of California, Los Angeles, and colleagues found carbon from biological sources inside zircons.

***

"We don’t have reliable measurements of atmospheric carbon dioxide from that long ago. But as far back as we can look, we see that there was a lot of it. In January 2020, Owen Lehmer,.. and colleagues published work analyzing the composition of meteorites from 2.7 billion years ago. They found that as the meteorites passed through our atmosphere, they preserved a record of the atmospheric composition. The researchers showed that it may have been 70% carbon dioxide or more, compared to just 0.04% today.

“'It’s really quite abundant in the atmosphere at that time,” said Lehmer. “Adding a bunch of carbon dioxide is certainly in line with keeping the young Earth warm and preventing a giant snowball.”

***

"Other recent work has suggested the faint young sun may not have been a problem at all, but a savior. Had the sun possessed between 92% and 95% of its present luminosity 4.5 billion years ago, Earth might have become too hot, resulting in a “steam Earth,” with water vapor unable to condense out of the atmosphere.

***

"In December 2020, Tyrrell calculated that Earth’s continuing habitability is mostly due to chance...“Earth’s success was not an inevitable outcome but rather was contingent,” he wrote. “It could have gone either way.”

Comment: So many factors, so much chance. But perhaps we are here under God's guidance. Be sure to see the explanatory illustration.