07/01/2010 04:13 pm ET Updated May 25, 2011

Multicellular 'Cookie' Fossils Found in Gabon

An international team of scientists said they've discovered fossils that may represent traces of the earliest-known multicellular life on the planet, dating back 2.1 billion years.

The cookie-shaped organisms -- uncovered in the west African country of Gabon -- would have existed when the planet was otherwise uninhabitable for modern-day plants and animals. Their discovery now suggests that multicellular life existed some 200 million years earlier than scientists had previously thought.

According to Philip Donoghue, a paleontologist as the University of Bristol, fossils of the organisms provide "the first record of that fundamental threshold in organismal complexity being surpassed." Noting that the fossils stretched as long as 4.75 inches (when previous fossils found from that period were microscopic and single-celled), he joked that their discovery was "like ordering an hors d'oeuvre and some gigantic thick pizza turning up."

Paleontologists collected more than 250 of the fossils from rock formations in Gabon. The 2.1 billion-year mark is significant because scientists believe the Earth's atmosphere underwent a major transition, called the "Great Oxidation Event," about 2.4 billion years ago. Before that time, the atmosphere would've been a toxic mix of greenhouse gases, without enough oxygen to sustain life.