Scientists in southwest Florida are exploring a "natural time capsule" in a deep spring, where the remains of humans and their tools date back 12,000 years -- the earliest evidence of human activity in the state.

Archeologist Carl J. Clausen reports in the Feb. 16 issue of Science magazine that further investigation of Little Salt Spring should provide new insights "into the subsistence of these early people and the environment in which they lived."

Scientists first thought Little Salt Spring, near Sarasota, was just another shallow pond typical of the region. But divers found a deep "sink hole" with two rock ledges 59 and 86 feet deep representing shorelines during periods of lower sea levels.

Clausen and four geologists said the earliest evidence of human activity was found on the lower ledge in the form on the lower ledge in the form of an overturned shell of an extinct species of a giant land tortoise.

A pointed stake, dated by radioactive techniques at 12,000 years old, had been driven into the tortoise. Fragments of fire-hardened clay were found around the animalhs remains, indicating the creature had been cooked upside-down in its shell.

Also found were remains of three extinct turtle species, an extinct sloth, an immature mammoth and an extinct bison.