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What Is High Blood Pressure?

High blood pressure is a blood pressure reading of 140/90 mmHg or higher. Both numbers are important. About one in every four American adults has high blood pressure. Once high blood pressure develops, it usually lasts a lifetime. The good news is that it can be treated and controlled. High blood pressure is called 'the silent killer' because it ...

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WhatIsHighBloodPressure
Geology

Seamounts - Underwater Mountains

Seamounts are undersea mountains that rise from the ocean floor, often with heights of 3,000 m or more. Compared to the surrounding ocean waters, seamounts have high biological productivity, and ... Continue reading

SeamountsUnderwaterMountains
Astronomy

Uncharted Meteors

In 1967, NASA's Mariner 4 spacecraft was cruising through the solar system, not far from Earth, when something unexpected happened. 'Mariner 4 ran into a cloud of space dust,' says Bill Cooke of the ... Continue reading

UnmappedMeteors
Geology

Devils Postpile National Monument

Established in 1911 by presidential proclamation, Devils Postpile National Monument protects and preserves the Devils Postpile formation, the 101-foot Rainbow Falls, and the pristine mountain scenery. ... Continue reading

DevilsPostpileNationalMonument
Chemistry

Table Salt - It's All In The Ions

All elements are defined by their individual atoms, which are in turn identified by the number of protons in the nucleus of each atom. Since protons are carriers of positive electrical charge, there ... Continue reading

TableSaltItsAllInTheIons

The Importance Of Clouds And Aerosols To Climate Change

CloudsAerosolsEverything, from an individual person to Earth as a whole, emits energy. Scientists refer to this energy as radiation. As Earth absorbs incoming sunlight, it warms up. The planet must emit some of this warmth into space or increase in temperature. Two components make up the Earth's outgoing energy: heat (or thermal radiation) that the Earth's surface and atmosphere emit; and sunlight (or solar radiation) that the land, ocean, clouds and aerosols reflect back to space. The balance between incoming sunlight and outgoing energy determines the planet's temperature and, ultimately, climate. Both natural and human-induced changes affect this balance, called the Earth's radiation budget.

Clouds affect the radiation budget directly by reflecting sunlight into space (cooling the Earth) or absorbing sunlight and heat emitted by the Earth. When clouds absorb sunlight and heat, less energy escapes to space and the planet warms. To understand how clouds impact the energy budget, scientists need to know the composition of cloud particles, the altitude of clouds and the extent to which clouds at different altitudes overlap each other. Both natural processes and human activities produce aerosols. They either reflect or absorb energy, depending on their size, chemical composition and altitude. The haze layer that is commonly seen in the summertime is one example of an aerosol that primarily reflects sunlight. Soot emitted by diesel engines is an example of an aerosol that absorbs sunlight. The reflection and absorption of energy by aerosols act in a direct way to change the balance between incoming and outgoing energy. These effects are called direct aerosol radiative forcing.

Aerosols also can affect the Earth's radiation budget indirectly by modifying the characteristics of clouds. Cloud particles almost always form around aerosols such as natural sea salt particles or human-made sulfate particles. The presence of additional aerosols can change the way clouds radiate energy and the length of time they stay intact. A good example is the way that exhaust particles emitted into the atmosphere by ships can increase the brightness of clouds along their course.