This map assembled from NASA radar data shows a shallow trough at the rim of the Yucatan crater. (Nasa) E-Mail This Article Printer-Friendly Version Permission to Republish Subscribe to The Post

Monday, March 10, 2003; Page A11

Count your blessings. Count them one by one. You may find yourself sleeping better, exercising more and caring more about other people.

New research shows that people who consciously remind themselves every day of the things they are grateful for show marked improvements in mental health and some aspects of physical health. The results appear to be equally true for healthy college students and people with incurable diseases, according to new research published in the Journal of Personality and Social Psychology.

College students asked to fill out a weekly report of five things for which they were grateful cited things such as "the generosity of friends" and "the Rolling Stones." Another group of students was asked to keep a daily diary for two weeks and express gratitude for things that had gone well each day. A third group, comprising adults with incurable diseases such as polio, were asked to write down what they were thankful for each day for three weeks.

Compared with similar groups who counted hassles, such as "hard to find parking" and "finances depleting quickly," the grateful groups felt better about their lives and more optimistic. The college students exercised more; the chronically ill adults reported sleeping longer and waking up refreshed.

The grateful people were also nicer to others and more willing to help people with personal problems, leading the researchers to conclude that "gratitude serves as a moral motivator."

Being grateful was also superior to its distant cousin -- seeing oneself as better off than others. People who took pleasure in troubles of others -- Schadenfreude -- had better mental health than those who counted hassles, but worse than grateful people.

The research was conducted by Robert A. Emmons at the University of California at Davis, and Michael E. McCullough of the University of Miami.

-- Shankar Vedantam

Within one of the most detailed topographic maps of North and Central America ever compiled, one very subtle feature stands out: evidence of Chicxulub, the enormous crater left when a comet or asteroid slammed into Earth about 65 million years ago, killing off the dinosaurs and much more.

The map, released last week, is based on radar data collected from space. The data for Chicxulub show a curving trough on the Yucatan Peninsula -- the boundary of the crater left when the celestial body did a cannonball in the Caribbean. The trough is 10 feet to 15 feet deep and three miles wide -- the crater is 3,000 feet deep and 112 miles wide -- but with computer enhancements, it shows up as a green arc cutting across the Yucatan's northwestern tip.

"Much of the surface expression of Chicxulub is so subtle, if you walked across it you probably wouldn't notice it," said Michael Kobrick, a scientist with NASA's Shuttle Radar Topography Mission, which collected the data. "That's where the view from space becomes invaluable."

That view was compiled in February 2000, when astronauts aboard the space shuttle Endeavour took three-dimensional radar measurements of Earth between 60 degrees north and 56 degrees south of the Equator -- 80 percent of the planet's landmass, and home to most of the world's population.

-- T.A. Frail

We are what we eat, especially when what we eat are bacteria that take up residence in our bodies.

A team of German researchers has drawn that conclusion by studying the genetic fingerprints of Helicobacter pylori retrieved from the stomachs of people representing 27 distinct ethnic, racial or geographic populations. The bacterium provides a good way of deducing the relatedness, and the physical migration, of different peoples around the world.

Many people acquire H. pylori in infancy, usually from a family member and most often from their mothers. The bacterium colonizes the lining of the stomach and lives for decades, becoming in some sense an extension of its host.

Geneticists use variations in the nucleotide sequence of human genes -- slight differences in the spelling of genetic "words" -- to determine when one group of people became physically separate from another, forming a distinct population. Linguists can make similar deductions by analyzing languages.

The German study, published in the journal Science, shows that by analyzing H. pylori's genetic variations, one can conclude that Inuit and American Indians split off from an East Asian ancestral population more than 12,000 years ago; that the Khoisan (Bushmen) peoples of South Africa are a more ancient population than their Bantu neighbors; and that Europeans are a mosaic of several populations.

Compared to other ways of plumbing mankind's prehistory, analysis of H. pylori is a fairly blunt instrument. The research is unlikely to shed light on current knowledge of human migration and ethnicity. However, it may help explain differences around the world in the prevalence of peptic ulcers and stomach cancer. Both conditions are caused, in part, by chronic colonization with the bug.

-- David Brown