The Hot Zone

Brave new world

Posted by Alison Hawkes on July 2, 2010
Category : Climates of the Past

It’s mighty hard to figure out what the Earth’s early atmosphere looked like some 4 billion years ago. But we know that it was hot — up to a stifling 153 degrees Fahrenheit, enough to melt wax.

This has always been a paradox. After all, the sun’s light was  30 percent dimmer back then, so there should have been glaciers covering the planet. Imagine what would happen if the Earth lost a third of its solar radiation today. Let’s just say there would be no outdoor barbecues on this Fourth of July.

Early Earth, artistic rendering, NASA

Early Earth, artistic rendering, NASA

The “faint early Sun paradox” is revisited in the journal Nature Geoscience this month with an article by Alicia Newton summarizing the newest theories on our newborn Earth’s climate. They come down to the kinds of greenhouse gases that shrouded the planet, and were vitally important in creating a climate back then, as they are today. Of course in both cases, then and now, the conditions of the atmosphere matter vitally to the development of life.

Jupiter’s moon Titan has long been looked towards as a atmospheric prototype for early Earth, since it’s thought to have  similarly high concentrations of Nitrogen, methane, and other hydrocarbons that produce a thick haze.

Artistic rendering of the surface of Titan, NASA

Artistic rendering of the surface of Titan, NASA

Researchers at the University of Colorado at Boulder are looking at how a similar haze of fractal organic aerosols might have both shielded the Earth from UV rays, necessary for life to develop, while allowing light to pass through and act as a greenhouse buffer.

The haze would have had other benefits, creating the soil from which life would grow. In a paper in the journal Science in June, Eric Woolf and Brian Toon write that the haze would have contained “complex organic molecules that would precipitate down into the primordial oceans, providing a source of organics to the surface comparable to current carbon burial rates.”

While today carbon dioxide is responsible for warming the atmosphere, research suggests that it wouldn’t have been back then.

The geologic history shows no evidence for high CO2 levels, writes Minik Rosing of the Nordic Center for Earth Evolution and colleagues in February’s journal Nature. Instead, they propose that the lack of dry land (and ice) would have kept the planet warm, since there would be less reflectivity back into the atmosphere.

Similarly, today we talk about “cloud seeding” as a way to cool the atmosphere by pumping up aerosols that will create the kind of clouds that reflect radiation back into space, rather than towards the Earth. Well, those kinds of clouds, produced in part by ocean phytoplankton belching out sulfate aerosols, would hardly exist in the early days. Making it warmer still.

The conditions that sparked life on Earth possible say a lot about what makes the continuation of life also possible. There’s more than one way to warm a planet.

-Alison Hawkes

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