Why Earth Is Not an Ice Ball: Possible Explanation for Faint Young Sun Paradox
ScienceDaily (May 30, 2012) — More than 2 billion years ago, a much fainter sun should have left Earth as an orbiting ice ball, unfit to develop life as we know it today. Why Earth avoided the deep freeze is a question that has puzzled scientists, but Purdue University's David Minton believes he might have an answer.
"If you go back in time to about 2 billion years ago, the Earth should have been frozen over," said Minton, an assistant professor of earth, atmospheric and planetary sciences. "There's a lot of geological evidence that the Earth wasn't frozen over. So, what is not equal? That is the Faint Young Sun Paradox."
Minton has offered a new explanation of why Earth avoided freezing over during a period when, according to geological and astrophysical observations, the sun burned at about only 70 percent of its current brightness. In short, he believes our planet might have been in a warmer place.
"I calculated to keep the Earth from being frozen over at the beginning of its history, it would have to be 6 or 7 percent closer to the sun than it is now," Minton said. "It's a few million miles, but from an orbital mechanics standpoint, it's not that far. The question is what could make a planet move from one location to another?"
Minton proposes Earth may have migrated from the sun over time through a process called planet-planet scattering, which occurs when one planet or more is ejected from its orbit, an increase in orbital separation occurs, or when planets collide. He presented his explanation recently at the Space Telescope Science Institute in Baltimore.
There are many possible ways a planet could move, but Minton said most alternatives could be ruled out because of the timeline involved.
"You have a huge time scale range from 1 billion to 10,000 years ago to work with," Minton said. "While most theories can be ruled out, planet-planet scattering is not ruled out. When a planet system or solar system forms there is no knowledge of how long they will be stable. They form and then they can go unstable in some time scale, and that time scale is set arbitrarily. Most of the instabilities happen early, and the longer you go in history, the more rare instabilities become. But rare does not mean never, and rare events can happen."
Minton speculates two proto-Venus planets existed at one point and went into a chaotic and unstable phase, crossing Earth's path and boosting us to our familiar orbit.
The two proto-Venus planets then collided, forming the planet Venus that exists today.
"One way we could have ruled this out would be if Venus had a geological history older than 2 billion years ago. We know, though, Venus is a relatively young planet."
The oldest surface on Venus is estimated to be 500 million to 700 million years old, a relatively young surface by planetary science standards. Impact craters on Earth can stretch back 1 billion to 2 billion years old, with a variety of ages on the surface.
"Venus looks like it became one age all at once," Minton said. "Venus could look like it does because at some point in the last billion years it was two planets that collided and had this catastrophic event. This hypothesis of the Faint Young Sun Paradox fits the evolution of Venus."
Minton will continue the research, which, if proven, could have several ramifications.
"It could say something about the evolution of life on Earth," Minton said. "Depending on when it happened, it could have had a major effect on the Earth's biosphere. You're basically shifting the Earth's orbit from one area to another pretty dramatically."
Minton said researchers from numerous disciplines have worked to solve the Faint Young Sun Paradox, including those from solar physics, astrophysics, geology, climatology and planetary sciences.
"It's one of the most all-inclusive subject areas in earth science because trying to understand it requires communicating with all of these different fields," he said.
ncient Climate: The Greenhouse Gas That Saved The World
ScienceDaily (Aug. 18, 2009) — When Planet Earth was just cooling down from its fiery creation, the sun was faint and young. So faint that it should not have been able to keep the oceans of earth from freezing. But fortunately for the creation of life, water was kept liquid on our young planet. For years scientists have debated what could have kept earth warm enough to prevent the oceans from freezing solid.
Now a team of researchers from Tokyo Institute of Technology and University of Copenhagen's Department of Chemistry have coaxed an explanation out of ancient rocks, as reported in this week's issue of PNAS.
A perfect greenhouse gas
"The young sun was approximately 30 percent weaker than it is now, and the only way to prevent earth from turning into a massive snowball was a healthy helping of greenhouse gas," Associate Professor Matthew S. Johnson of the Department of Chemistry explains. And he has found the most likely candidate for an archean atmospheric blanket. Carbonyl Sulphide: A product of the sulphur disgorged during millennia of volcanic activity.
"Carbonyl Sulphide is and was the perfect greenhouse gas. Much better than Carbon Dioxide. We estimate that a blanket of Carbonyl Sulphate would have provided about 30 percent extra energy to the surface of the planet. And that would have compensated for what was lacking from the sun," says Professor Johnson.
Strange distribution
To discover what could have helped the faint young sun warm early earth, Professor Johnson and his colleagues in Tokyo examined the ratio of sulphur isotopes in ancient rocks. And what they saw was a strange signal; A mix of isotopes that couldn't very well have come from geological processes.
"There is really no process in the rocky mantle of earth that would explain this distribution of isotopes. You would need something happening in the atmosphere," says Johnson. The question was what. Painstaking experimentation helped them find a likely atmospheric process. By irradiating sulphur dioxide with different wavelengths of sunlight, they observed that sunlight passing through Carbonyl Sulphide gave them the wavelengths that produced the weird isotope mix.
"Shielding by Carbonyl Sulphide is really a pretty obvious candidate once you think about it, but until we looked, everyone had missed it," says Professor Johnson, and he continues.
"What we found is really an archaic analogue to the current ozone layer. A layer that protects us from ultraviolet radiation. But unlike ozone, Carbonyl Sulphide would also have kept the planet warm. The only problem is: It didn't stay warm."
Life caused ice-age
As life emerged on earth it produced increasing amounts of oxygen. With an increasingly oxidizing atmosphere, the sulphur emitted by volcanoes was no longer converted to Carbonyl Sulphide. Instead it got converted to sulphate aerosols: A powerful climate coolant. Johnson and his co-workers created a Computer model of the ancient atmosphere. And the models in conjunction with laboratory experiments suggest that the fall in levels of Carbonyl Sulphide and rise of sulphate aerosols taken together would have been responsible for creating snowball earth, the planetwide ice-age hypothesised to have taken place near the end of the Archean eon 2500 million years ago.
And the implications to Johnson are alarming: "Our research indicates that the distribution and composition of atmospheric gasses swung the planet from a state of life supporting warmth to a planet-wide ice-age spanning millions of years. I can think of no better reason to be extremely cautious about the amounts of greenhouse gasses we are currently emitting to the atmosphere."
