Thursday, November 29, 2007

Triumph of Light Pt. 2

New York, Rockefeller Center November 28, 2007

From above Times Square Tuesday, this night we have descended into the milling crowd. Wednesday was the 75th lighting of Rockefeller Center’s Christmas tree! While waiting in the cold, we were serenaded by celebrities from Tony Bennett to Carrie Underwood. With a nod to energy conservation, this year the tree is lit with 30,000 light-emitting diodes. Solar panels placed on Rockefeller Center’s rooftops provide some of the electricity. As the holidays are a season of hope, this tree again demonstrates that “dark energy” does not dominate the Universe.

This Norway Spruce grew in Connecticut before being harvested and shipped to Manhattan. An image of hope is also a reminder that our time on Earth is limited. Though the felling of a tree can be sad, there are many more trees growing. If old trees were not removed, the forest would face greater danger from fire. Tree growers in the US are now required to plant more than they fell. Despite all the threats, trees continue to grow, life continues to form and evolve new structures.

While the solar panels are a nice touch, most of New York’s electricity still comes from fossil fuels. Petroleum and coal are formed deep within Earth, when organic molecules encounter interior heat. Source of Earth’s core heat has long been a mystery. Most radioactive elements have half-lives of only a few million years. The old hypothesis of “radioactive decay” cannot explain why the core remains hot after 4.6 billion years.

If Earth indeed formed around a Black Hole, than this tiny object would give off Hawking radiation indefinitely. It would be far too small (0.5 millimeters) to sick us up, but the small amount that it eats has kept Earth warm for several billion years. The radiation produced would eventually make its way to the surface as heat. Some of that heat converts chemicals to fossil fuels which humans use for energy.

The lighting of this tree shows that “dark energy” does not dominate; the Universe continues to create luminous structures. Primordial Black Holes are relics of a time near the Big Bang. Energy from a Black Hole eventually finds its way into fossil fuels, which power New York lights. Even solar power originated in a Sun born around a primordial Black Hole. If not for their quiet presence, our planet and Solar System would not have formed. This Happy Holiday is courtesy of a Black Hole!

NEXT: Where the day was spent, a place more exciting for science.



Blogger nige said...

Louise, thanks for a very nice post.

"Source of Earth’s core heat has long been a mystery. Most radioactive elements have half-lives of only a few million years. The old hypothesis of “radioactive decay” cannot explain why the core remains hot after 4.6 billion years."

Ummm, tere's historically been a lot of controversy over the exact contributions of different sources of heat.

The half-life of uranium-238 (99.3% of natural uranium), 4,460 million years, is almost the same as the age of the Earth, 4,540 million years. So that's a good source at least in part, for the Earth's heat (depending on how the uranium is distributed within the Earth, but since uranium is chemically a refractory element it should be quite uniformly mixed).

Thorium-232 is also extremely abundant and a major source of natural heat. It has an even longer half-life (about the age of the universe), 14,000 million years, so most of it is still around.

Also important is naturally radioactive potassium-40, which is 0.0117% of natural potassium and is far more abundant in most rocks than uranium and has a half-life of 1,260 million years.

I recall around 1988 trying to find out exactly why the Earth's core remains hot by reading the relevant articles in Encyclopedia Britannica at school.

The edition I was reading did not even mention radioactivity as a source of the Earth's internal heat. Instead, it claimed that the heat produced was latent heat released in the exothermal reaction whereby the molten core gradually solidified at the outer edges, similar to the rise in temperature you get when water vapour condenses into water droplets. (This is Kelvin's old theory which was disproved over a century ago by Darwin's evolution and the discovery of radioactivity, but that encyclopedia still hadn't updated it's discussion by 1988.)

There are also arguments about other mechanisms, for example heat energy is given off just as a result of the Moon orbiting the Earth, because the Moon doesn't orbit the Earth's core but a point along the line between the Earth's core and the Moon's core that is within the Earth but not in the very middle. As a result, the forces involved tend to have tidal effects on the molten core, and energy is delivered at the long-term expense of the Moon-Earth orbit (which gradually loses kinetic and potential energy as energy is delivered to the Earth's core).

2:05 AM  
Blogger L. Riofrio said...

This thoughtful comment shows why there has been a mystery. U-238 has a long half-life, but is not likely to exist in the core (1) because its abundance in the crust is only about 3 parts per million, (2) it does not mix with iron and would not sink to the core of a molten planet (3) meteorites dating from time of Earth's formation have virtually no Uranium. Most previous speculations focus on Potassium 40, which is thought to be more common (1.5% of Earth's crust) and has half-life of 1.277 Gyr.

As far as is known Earth's core formed from nickel and iron, with radioactive elements arriving later. The crust is thought to contain most of the radioactive elements, which begs the question why the core is hotter than the crust.

Jupiter and Saturn have almost no radiactive elements yet generate immense heat. The giant planets make one wonder whether those processes exist within Earth.

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