In keeping with the theme of TED2008, professor Stephen Hawking asks some Big Questions about our universe -- How did the universe begin? How did life begin? Are we alone? -- and discusses how we might go about answering them.

The world today teems with life. Where ever you look something is alive. Then imagine 95 percent of it dying in the blink of a geological eye. It's not a fantasy, it did happen, two hundred and fifty million years ago. It was the day the Earth nearly died.

Scientists describe the discovery of organic molecules on the planet HD 189733b (Courtesy NASA/ESA/M Estacion/STScI)

''Can we create new life out of our digital universe?'' asks Craig Venter. And his answer is, yes, and pretty soon. He walks the TED2008 audience through his latest research into ''fourth-generation fuels'' -- biologically created fuels with CO2 as their feedstock. His talk covers the details of creating brand-new chromosomes using digital ...

As we go through our lives -- driving cars, exploring the Internet, studying the world around us -- it is hard to imagine that we're related to Earth's other animals. It's even a stretch to see what connects us with the rest of the chordates, a group of about 50,000 species including the vertebrates like fish, amphibians, reptiles and birds, ...

It's easy to believe that animals like us, creatures with heads, eyes, and brains, are the crowning achievement of evolution. But are we really? Echinoderms like sea stars, sea urchins, and sea cucumbers have no head, eyes, or centralized brains, yet they have proven themselves worthy competitors. In fact, they can live in places inaccessible ...

Behind the beautiful shapes and colors of seashells is the story of how a group of animals called molluscs evolved in order to survive. The wide variety of molluscs includes clams, oysters, snails, mussels, squid, and octopus. The word mollusc comes from Latin meaning ''soft,'' a good description of the group's fleshy bodies. Of course, in an ...

For hundreds of millions of years, animal life resided only in the oceans. And then about 400 million years ago, fossil tracks suggest that an animal called a eurypterid left the water to walk on land. Maybe it was fleeing enemies, maybe it was searching for an easy meal, or maybe it was seeking a safe place to lay its eggs. Eurypterids were ...

In the 4.5 billion year history of Earth, a mere 10 million years seems rather insignificant, the equivalent of two months in the life of a 75 year-old man. Yet, during a 10 to 20 million year stretch of time, beginning about 540 million years ago, life evolved at an explosive rate. Scientists call the period the ''Cambrian Explosion.'' ...

The best way to find food is to go out and hunt for it. But to hunt, you need to be able to move forward. And to move forward, you usually need a head with paired sense organs to know where you are going attached to a symmetrical body to get you there. Scientists believe that a flatworm-like animal was the first creature to develop a head, ...