Could life on Earth be much older than supposed?

A team of researchers based at the Curtin University of Technology near Perth, Australia, believe they have evidence that life may have begun 700 million years earlier than traditionally assumed. According to their July 3, 2008 announcement,

The 4.2 billion year old diamonds found trapped inside the Jack Hills zircon crystals are the oldest-known samples of Earth’s carbon. The Curtin led team’s discovery of very high concentrations of carbon 12, or “light carbon” within these crystals is remarkable as it is a feature usually associated with organic life.

[ ... ]

Evidence for ancient life stretches back in time to at least 3.5 billion years ago, in the form of single-celled organisms that did not require oxygen. The discovery of light carbon in the Jack Hills crystals raises the question – did a simple life form exist on Earth 700 million years earlier than previously thought?

According to geologist team leader Alexander Nemchin,

The discovery challenges our fundamental understanding of processes active in the early history of the Earth. It suggests that life may well have appeared on Earth long before the period of heavy-meteorite bombardment believed by some to have initiated the emergence of life on Earth.

Alternatively, light carbon doesn't necessarily signal life.

If life really appeared on Earth long before heavy meteor bombardment, theories that involve any kind of gradual Darwinian process for the origin of life are pretty much dead.

We are then left with either an extraterrestrial origin of life or an origin coded into the formation of Earth itself - an intelligent design hypothesis.