How the Earth Was Made

Almost 200 miles long and over a mile deep, this deep scar in the American Southwest is easily visible from space. You could stack five Empire State Buildings one on top of the other--and they still wouldn't reach the lip of the Canyon. As the Pacific grinds into the North American plate, a giant plateau has been pushed up over a mile in the air. Meanwhile, the Colorado River has been draining the Rockies, and with its thick load of sediment, continues to carve this amazing canyon in the rising plateau.

Mt Vesuvius is the world's most dangerous volcano, and it threatens three million people. It was responsible for the most famous natural disaster of ancient history, the eruption that destroyed the Roman city of Pompeii. And its most recent blast was caught on film in 1944. Today Vesuvius is the most densely populated volcano in the world. Now recent scientific discoveries show that it is capable of an eruption larger than ever before thought possible and that hidden beneath Vesuvius there is a vast magma chamber of boiling hot rock, ready to come out.

Four and a half billion years ago the Earth formed from dust in space to become a molten ball of rock orbiting the Sun. This episode travels back in time to investigate how the fledgling planet survived a cataclysmic cosmic collision with another world, how molten rock solidified to land, how our oceans filled with water and how life arrived on Earth. Geologists study the oldest rocks on Earth and meteorites from outer space to solve the greatest geological mystery of all--the Birth of the Earth.

Africa's Sahara Desert is the size of the United States, making it the largest desert in the world. It's also the hottest place on the planet. But now an astonishing series of geological discoveries has revealed this searing wasteland hides a dramatically different past. Scientists have unearthed the fossils of whales, freshwater shells and even ancient human settlements. All clues to a story that would alter the course of human evolution and culminate in biggest climate change event of the last 10,000 years.

The Sierra Nevada, North America's highest mountain range, contains one of the most awe-inspiring geological features on the planet: Yosemite Valley. Walled by sheer 3,000-foot granite cliffs and made from one of the toughest rocks on earth, it is home to the mighty El Capitan and iconic Half Dome. Yet how this extraordinary valley formed has been the subject of controversy for over 100 years. Was it carved by gigantic glaciers or a cataclysmic rifting of the Earth?

From Alaska to New Mexico, the Rockies are one of the great mountain belts of the world--caused by tectonic forces of the Pacific Plate pushing against the North American continent. They have formed as the earth's continental crust has been shortened under pressure--by around 1 inch a year. What's more, they are still rising and they are still young in geologic terms: when the dinosaurs roamed the Earth they had not even started to form.

The single longest linear feature on Earth--the "Ring of Fire" circles almost the entire Pacific. It is a ring of active volcanoes from White Island just north of New Zealand, through the South China seas, Japan, Kamchatka, the Aleutians, the Cascades and down through the Andes. Almost 25,000 miles long, it is one of the most awesome sights on Earth.

It is the tallest and biggest mountain on earth, as far removed from sea level as it's possible to be--and yet its sedimentary layers contain fossils that were once creatures that lived on the ocean seabed. The Himalayas formed when India smashed into Asia--propelled by plate tectonics. Everest is still rising but its height is limited--extreme erosion counteracts and limits the amount of uplift.

It is not only a place of natural splendor but a geologic treasure trove as well. Hidden in the sediments of the rocks in its walls is evidence of the coldest time on our planet--ironic in one of the hottest places on Earth. Death Valley is literally being pulled apart and the floor is collapsing and lower than sea level. Here and across much of Nevada is the Basin and Range province--a series of ridges of mountain ranges that are being pulled apart and the basins between them getting wider and flat as they fill with eroded sediment.

Over 20 years ago, Mt. St Helens--thought to be dormant--shocked America when it exploded. It is an acidic volcano--the magma beneath is full of volatiles making it highly explosive. A new plug has formed in its throat and is rising. When it blows it will be like uncorking a champagne bottle, releasing pressure below and allowing dissolved gases to escape and explode. The question is...when will it blow again?

In the remote wastes of Siberia buried under snow are the remains of one of the greatest catastrophes that the Earth has endured. 250 million years ago, huge volumes of lava spewed out onto the surface--so much that it would have buried the whole of Texas under one mile of lava. At first the temperature dipped but then the greenhouse gases that escaped from the depressurized lava caused a massive global warming. It wreaked havoc and 95% of the species on Earth became extinct. Yet life hung on and in time this disaster paved the way for the next great phase of life on earth--the age of the dinosaurs.

Why do we have ice ages and when is the next one due? Chart the progress of different ice ages through the history of our planet, from Snowball Earth hundreds of millions of years ago to the recent ice ages. As the Earth circles the sun, its orbit changes slightly and so does it angle of rotation. When the right wobble in our rotation combines with the right orbit, the Earth is, and will again be, plunged into an ice age--but maybe not for a few thousand years.

Gold dates from the time of the supernova explosion that gave birth to the building blocks of our solar system. When it was created, the Earth included a tiny percentage of gold atoms, and over the aeons geologic processes have concentrated it into various nooks and crannies around the globe. The best of it is in the ancient Precambrian rocks in South Africa, where the deepest mines in the world extract it. In other regions of the world, gold can be gathered from younger sedimentary rocks that have been eroded off older Precambrian rocks. The American gold rush was this type of deposit. Now in Nevada, sedimentary rocks are leached on a truly vast scale to extract the gold.