Daffodils, tulips, roses and other flowers are so much a part of our daily lives that we take them for granted.
But to evolutionary scientists, the question of how and when flowering plants appeared on Earth has gone unanswered for more than a century.
Mosses were the first plants to emerge on land some 425 million years ago, followed by firs, ginkgoes, conifers and several other varieties.
According to the fossil record, flowering plants abruptly appeared out of nowhere about 130 million years ago.
Where did they come from, and how could they have evolved so suddenly without any transitional fossils linking them to other ancient plant species?
"An abominable mystery" is how nineteenth-century naturalist Charles Darwin referred to the origin of flowering plants, and the puzzle remains as controversial today as ever.
Now a team of Stanford geochemists has entered the debate with evidence that flowers may have evolved 250 million years ago - long before the first pollen grain appeared in the fossil record.
"Our research indicates that the descendants of flowering plants may have originated during the Permian period, between 290 and 245 million years ago," says J. Michael Moldowan, research professor of Geological and Environmental Sciences.
"We based our findings on an organic compound called oleanane, which we found in the fossil record," he adds.
Moldowan and his collaborators, research associate Jeremy Dahl and graduate student David A. Zinniker, will present their findings at the annual meeting of the American Chemical Society (ACS) in San Diego on April 2, during a symposium titled, "Biogeochemistry of Terrestrial Organic Matter."
Oleanane is produced by many common flowering plants as a defense against insects, fungi and various microbial invaders. But the chemical is absent in other seed plants, such as pines and gingkoes.