On Easter Day 1722, Dutch explorers landed on Easter Island. A civilisation isolated by 4,000km of Pacific Ocean was about to meet the outside world for the first time in centuries. The strangers were about to find something very strange themselves - an island dotted with hundreds of huge stone statues and a society that was not as primitive as they expected. The first meeting was an immense clash of cultures. (Bloody too: the sailors killed ten natives within minutes of landing.) Where had the Islanders originally come from? Why and how had they built the figures? Modern science is piecing together the story, but it is far too late for the Easter Islanders themselves.

Sleeping is an essential part of everyone's life yet it remains little understood is barely understood. You might think it's a relaxing recharge but in fact your brain is working harder at times overnight than when you're conscious in the day.

The Earth is under constant bombardment. Each year, many fragments of debris hit our planet. Fortunately for us, most are so small that they burn up harmlessly in the atmosphere.

A dirty bomb is a radiological weapon but unlike a nuclear bomb, its purpose is to contaminate rather than destroy. It uses normal explosives to disperse radioactive materials in the local environment, creating a hazard to health that could last for years unless cleaned up.

The drug Viagra revolutionised the treatment of sexual dysfunction in men on its launch five years ago. An accidental discovery, the tablet that gave impotent men the chance once more to have natural erections became the fastest selling pill in history and has earned its manufacturer, Pfizer, over $6bn.

Understanding of humans' earliest past often comes from studying fossils. They tell us much of what we know about the people who lived before us. There is one thing fossils cannot tell us; at what point did we stop living day-to-day and start to think symbolically, to represent ideas about our environment and how we could change it? At a dig in South Africa the discovery of a small piece of ochre pigment, 70,000 years old, has raised some very interesting questions.

It was the simplest idea but one with enormous potential. If a gene is defective in the human body, just replace it with one that works properly. Gene therapy would mean that genetic disorders would become a thing of the past. Cancer would be cured, as would cystic fibrosis and hundreds of other genetic illnesses. Scientists were justifiably excited about the idea but, this enthusiasm that would end up costing one young man his life.

Earthquakes are among the most devastating natural disasters on the planet. In the last hundred years they have claimed the lives of over one million people. Earthquakes are destructive mainly because of their unpredictable nature. It is impossible to say accurately when a quake will strike but a new theory could help save lives by preparing cities long in advance for an earthquake.

Are we alone in the Universe? Or are there aliens somewhere in space? New evidence suggests not only might other life-forms be out there, they may even be living on the planet right next door to us - Mars.

Set against the back drop of awe inspiring geological beauty, a strange scientific adventure sets out to discover how a mineral clad cave network - the height of a 30 storey building and the length of six football fields - came to exist deep below the Guadalupe Mountains in North America.

Rudi Affolter and Gwen Tighe have both experienced strong religious visions. He is an atheist; she a Christian. He thought he had died; she thought she had given birth to Jesus. Both have temporal lobe epilepsy.

265 people died when an Airbus operated by American Airlines crashed into the New York suburb of Queens in November 2001. The twin-engined jet took off from John F Kennedy Airport in fine conditions but hit trouble after just 67 seconds. In the following 38 seconds the plane started to disintegrate before nose-diving into the residential Rockaway area of the city.

Severe Acute Respiratory Syndrome didn't even have its name in February 2003, when it struck its first known victim, Johnny Cheng, in Hanoi, Vietnam. Within days, an international effort led by the World Health Organization (WHO) had massed scientific expertise to fight the mystery illness and avert the nightmare scenario of an uncontrollable pandemic sweeping the globe.

Remember that long, hot summer? You might never see its like again. And all that talk of global warming? Forget it.

This week Horizon investigates the science behind the Bible Code.

Mixing powerful and deeply moving footage with telling forensic analysis, Horizon reveals what really went wrong on the Space Shuttle Columbia. The film's final revelation is telling. If NASA had acted differently, all seven astronauts could have been brought back to Earth alive.

Horizon tells the microbiological detective story in which some of the best brains in science have been pitted against the most extraordinary bug the world has ever seen.

Could an unknown Englishman have been the first person ever to fly?

Horizon's Time Trip is a thrilling journey deep into the strangeness of cutting-edge physics - a place where beautiful, baffling ideas are sometimes indistinguishable from the utterly crazy.