On the horizon

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Still room to grow

Is there a height beyond which no tree can grow, and have the world's tallest trees - California's redwoods - reached their max?

Scientists recently tackled those questions. Their findings, published in the journal Nature, suggest that trees cannot grow more than 400 to 426 feet tall. That means that the world's tallest tree - a 370-foot redwood - could still add 56 feet. At average growth rates, that would take 224 years, said lead researcher George Koch of Northern Arizona University.

To get their data, Koch and his colleagues went into the treetops of five of the eight tallest trees on Earth and used sophisticated instruments for measuring water tension and photosynthesis. Their experiments showed that tree height is limited by the physics of hauling water from the ground. The work of raising that water starts at the outer greenery: As water molecules get absorbed through pores in leaves or needles, they draw other water molecules up behind them through narrow tubes that run from roots to treetop.

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At about 413 feet, the team found that upward force is equally matched by gravity, placing a cap on cell growth and photosynthesis.

New mineral from the moon

A new mineral formed by repeated bombardments from meteorites and other space debris has been found in a meteorite that fell to Earth from the moon in 2000. The finding shows that "space weather" can help create materials not found on Earth, researchers reported in this week's issue of the Proceedings of the National Academy of Sciences.

The new mineral, made of iron and silicon, is named hapkeite after Bruce Hapke, a scientist who predicted the process that forms the mineral.

Airless bodies such as the moon, Mercury, and asteroids have an inorganic soil made of crushed rocks called regolith. In theory it is formed by the impact of micrometeorites traveling at high speed. The heat from their impact melts and vaporizes metals, which are then redeposited on rock fragments. Hapkeite is made when iron and silicon are deposited with two parts iron and one part silicon, researchers reported.

UN Nukes mosquitoes

The United Nations is harnessing nuclear technology to try to eradicate malaria-carrying mosquitoes. The UN is particularly interested in combating the disease in sub-Saharan Africa.

The UN International Atomic Energy Agency (IAEA) has already used its expertise to wipe out the tsetse fly - associated with the transmission of fatal sleeping sickness - from Zanzibar.

To combat malaria, scientists would breed insects and expose the males to enough radiation to render them sterile. The males are then released into the wild to breed with females, whose eggs are unfertilized and never hatch.

"The population would actually start to crash and [that] eventually may actually lead to eradication of the insect, and therefore eradication of the disease," said Bart Knols, a Dutch entomologist at IAEA. In the '70s, El Salvador successfully used the same technique to eradicate malaria from part of that country.

However, an IAEA entomologist said there are still many hurdles to overcome in the current project.

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