The plan is to trace the family ties between everything from bacteria to whales, from dinosaurs to humans, using the latest tools of biology, genetics and computer science.

Scientists say this huge genealogical chart will have practical benefits for medicine, agriculture and the environment, as well as providing a basic understanding of life on our planet. They say it will be as valuable as the chemists' familiar Periodic Table of the Elements, only much larger and more complex.

One of the amazing claims of modern biology is that all life on Earth is descended from one common ancestor, a one-celled microbe that appeared 4 billion years ago. As ages passed, this tiny organism multiplied, differentiated and evolved into the enormous array of species that have since populated the Earth.

More than 1.75 million species of organisms are known to science, but 10 times that many probably remain to be identified.

"We humans use the Earth in so many ways, it's like a company that has a big warehouse of products but doesn't know what's in the warehouse," said Diana Lipscomb, director of the Assembling the Tree of Life program at the National Science Foundation. "We need to do this stock-taking."

The project is expected to take 10 years and cost about $150 million. Hundreds of scientists and dozens of universities and research organizations will be involved. The first batch of grants, totaling $17 million, was approved in November. A second round of requests is due in May.

"Learning about these species and their evolutionary history is epic in scope, spanning all the life forms of an entire planet over their several-billion-year history," Lipscomb said. "There is no way to know how modern species are related without knowing their ancestry."

One of the first grants, for $1.7 million, went to Mark Norrell, a paleontologist at the American Museum of Natural History in New York, to settle the controversial relationship between birds and dinosaurs. Scientists think birds descended from a breed of dinosaurs known as theropods, which also produced the notorious Tyrannosaurus rex, but confirmation is needed.

Earlier versions of the ancestral chart -- technically known as a phylogenetic tree -- already have been used to diagnose and treat disease.

For example, researchers used this technique to swiftly identify the lethal hanta virus that was discovered in the Four Corners area of New Mexico in 1993. The virus' genetic makeup was unlike anything previously reported, but the phylogenetic tree of known viruses showed that its closest relatives were other hanta viruses from Asia. The degree of closeness was determined by counting the number of differences between the genes of the Four Corners virus and other viruses.

"This identification was possible only through phylogenetic analysis of the virus, which allowed very rapid identification," said David Hillis, a biologist at the University of Texas in Austin.

A better source of Taxol, the breast-cancer drug, was discovered by tracing the genetic relationship between Taxol's original source, a rare yew tree, and a more common shrub.

Hillis uses phylogenetic techniques to research the origin and predict the course of HIV, the virus that causes AIDS. He also studies harmful invasions by alien species, such as Asian clams that clog the cooling systems of power plants in the United States.

To construct the tree of life, scientists use the latest information from DNA sequences, as well as older methods of comparing creatures' shapes, organs and behavior to determine their relationships. Like a living fossil, DNA preserves a record of an organism's ancestry.

Anthropologists say humans and chimpanzees shared a common ancestor 5 million to 7 million years ago. We primates -- humans, apes and monkeys -- grew up in the family of mammals, which sprouted from the class of vertebrates, a subdivision of the kingdom of animals. Animals, in turn, are a twig on the great branch of creatures that shelter their DNA inside the nucleus of each of their cells.