Swedish biologists have extracted long segments of DNA from a 2,400-year-old Egyptian mummy, revived the heredity-bearing molecules and grown multiple copies of them in bacteria.

The achievement proves that ancient preserved human bodies, like more recent ones, may retain their genes in a form that molecular biologists can recover and read.

Because preserved human remains are found in many parts of the world, including mummies in Peru, Japan, Australia and Europe -- the method opens the door to a wide range of investigations of relationships among the world's ancient peoples.

It should be possible to compare mummy DNA with that of other peoples, living and dead, and settle such long-simmering arguments as who the ancestors of the pharaohs were and how the various dynasties were related.

DNA, the long-chain molecules whose structure encodes the heredity of every organism, carries the most detailed evidence possible of kinships on every scale from that of parent and child to that of one species and another.

The new findings were reported in Nature, the British scientific journal, by Svante Paabo of Sweden's University of Uppsala.

Paabo found the DNA in a patch of dried skin cells removed from the left lower leg of a mummified baby boy in the Egyptian Museum in East Berlin.

In 22 other mummies he examined, DNA cells had disintegrated.

The Berlin mummy's cells were rehydrated and the DNA segments extracted using much the same methods as molecular biologists use on living tissue.

The DNA segments were spliced into the DNA of bacteria, which then reproduced the mummy DNA as if it were bacterial DNA.

The largest mummy segment measured 3,400 bases long. Bases are the various units that are chained in sequence to make a strand of DNA.

A single gene may be a few hundred to several thousand bases long; a typical human cell contains about 6 billion bases.

Using conventional methods, Paabo determined the sequence of bases in the mummy DNA and found that it contained certain standard segments that are repeated many times in normal human DNA.

Because the segments agreed in sequence with those of living humans, Paabo concluded that the mummy DNA had survived with little or no alteration from its state in life. The formation of the solar system may have been very rapid, converting a vast cloud of gas and dust into a star with a family of very different planets in as little as a few million years, astrophysicists have concluded.

Astronomers consider the period surprisingly brief compared to older speculation that the process took hundreds of millions of years.

A few million years is even shorter when contrasted with the 4.5 billion years the solar system has existed since its formation.

The new estimate is based on the calculations of Douglas N.C. Lin of Lick Observatory, which is part of the University of California at Santa Cruz.

Lin's model is one that Kant and Laplace would have recognized as a descendent of their 18th-century theory.

In general, the story begins with a swirling cloud of loose molecules -- mostly hydrogen -- drifting in space.

In the regions where density was greatest, the molecules' gravitational pulls added up to draw in more and more molecules, forming a spinning ball that was denser as one moved toward its center.

The center of the ball became the sun when its density produced heat great enough to ignite nuclear fires.

Simultaneously, the rare heavier particles of solid matter -- iron, silicon and the like -- gathered into clumps that orbited the sun at various distances. As clumps grew, many joined, eventually creating the known planets.

Lin's calculations suggest that the relatively small inner planets -- Mercury, Venus, Earth and Mars -- stopped growing because they had swept up all the nearby solid matter.

The giant planets -- Jupiter, Saturn, Uranus and Neptune -- began the same way but, having access to particles not scooped up by the sun, formed large enough solid cores to produce the gravity that could capture large volumes of gas from the primordial cloud. These planets are predominantly gas.

Pluto, anomalous in many ways, is not accounted for in this scenario. A water molecule that evaporates stays in the air an average of 10 days before it falls back to Earth as rain, according to John Woods of West Germany's University of Kiel.

If the molecule lands in a large lake, it could stay there about 100 years.

If it lands in the ocean, it may not escape for 3,000 years.

Should that molecule happen to drift over the poles and become part of a rare snowflake in those regions, it could get trapped in a glacier for tens of thousands of years.