Behind the Earth

While large, relatively young volcanoes can be found on Venus, those on Mars are very old. The Earth also has many volcanoes on its surface but its great originality, compared to its two direct neighbours, lies in plate tectonics. Why are Mars and Venus so geologically different? How can we explain why the red planet's magnetic field quickly went out? What were the consequences on its evolution? Francis Albarède, a geochemist at the Earth Sciences Laboratory in Lyon, explains.

Today the oceans cover 71% of the Earth's surface. But this was not always so! At the beginning of its history, the Earth was probably a dry planet. So, where did all this water come from? Francis Albarède, a geochemist at the Earth Sciences Laboratory in Lyon, gives us his hypothesis.

In the large family of volcanoes, there are grey and red volcanoes. There are those that explode and those that produce fluid lava flows. But are these differences significant for scientists? Sylvie Vergniolle, a volcanologist at the Institut de Physique du Globe de Paris (Paris geophysical institute - IPGP), discusses the similarities between the Fuji-Yama in Japan, the Soufrière in Guadeloupe and the Montagne Pelée in Martinique. In addition, she explains how the Piton of la Fournaise of…

Volcanic eruptions are always spectacular with their huge flows of incandescent lava and fragments of magma projected several tens of kilometres away into the atmosphere. Still one may wonder what they are caused by. From the pressure cooker to a glass of beer and the honey pot, Sylvie Vergniolle, a volcanologist at the Institut de Physique du Globe de Paris (Paris geophysical institute - IPGP), has put together a small selection of cooking metaphors to help us understand how volcanoes work…

In the time scientists have been studying volcanoes, have they learned to detect the warning signs of an eruption? To what extent is it possible to anticipate these natural disasters? And today, what is the most monitored volcano in the world? Those are the questions answered by Sylvie Vergniolle, a volcanologist at the Institut de Physique du Globe de Paris (Paris geophysical institute - IPGP).

If we observe the Earth's magnetic field, everything happens as if there were a gigantic magnetic bar at the heart of our planet running approximately along its axis of rotation, with at its ends the south pole and the magnetic north pole. But one has to look below the surface, as shown by Jean-Pierre Valet, a paleomagnetician at the Institut de Physique du Globe de Paris (Paris geophysical institute - IPGP), who tells us what is really going on under our feet.

Jean-Pierre Valet who is a paleomagnetician at the Institut de Physique du Globe de Paris (Paris geophysical institute - IPGP) explains how the magnetic field surrounding the Earth protects us. Where did it come from? How does it change? If compasses had existed 800,000 years ago, their needles would have pointed... south! Since the Earth's magnetic field has existed, it has reversed many times. How did scientists discover our planet's stunning magnetic past? Should we expect the Earth to…

Jean-Pierre Valet, a paleomagnetician at the Institut de Physique du Globe de Paris (Paris geophysical institute - IPGP), explains how pole inversion works. In the past, the Earth's magnetic field has reversed many times and, one day or another, the North Magnetic Pole will return to the geographic South Pole. During these transition phases, would there be cause for concern about the weakening of the magnetic shield that protects the planet from cosmic radiation? Should we also be…

Alain Prinzhofer is a geochemist at the Institut de Physique du Globe de Paris (Paris geophysical institute - IPGP), and he wonders how long it will take for Humanity to exhaust the reserves that our planet has taken millions of years to build-up. Where are our remaining oil, coal and natural gas stocks? Do researchers already have any idea on how to replace these fossil fuels when they become scarce?

Alain Prinzhofer is a geochemist at the Institut de Physique du Globe de Paris (Paris geophysical institute - IPGP) and he explains why the price of raw materials is rising more than that of the oil barrel. Why, for example, has copper or helium become so expensive? Have we already exhausted all the resources of our planet? Can we still hope to discover new mines and new deposits?

Alain Prinzhoferis a geochemist at the Institut de Physique du Globe de Paris (Paris geophysical institute - IPGP) and he describes the new sources of energy. Deep at the bottom of the oceans, where continental plates are drifting apart, scientists have discovered sources of hydrogen gas. This gas is of great interest to researchers because it is a particularly clean source of energy. One may wonder if it has a future. Could it stand a chance to replace oil?

Gabriel Gohau is a historian at the REHSEIS laboratory in Paris and relates our ancestors' representation of our planet, its oceans, its sky and its volcanoes. From Aristotle, four centuries BC, to Leonardo da Vinci, in the 15th century, the Earth hardly changed in scholars' minds. It was unthinkable that it was anywhere but the centre of the world. What discoveries have changed certainties?

Gabriel Gohau is a historian at the REHSEIS laboratory in Paris and tells the history of the theories concerning the formation of planet Earth. It was in the middle of the 16th century that Copernicus realized that the Earth was not at the centre of the universe. This is how some scientist were then prone to explain how our planet was formed. Many "theories of the Earth" flourished. Often more poetic than scientific, these theories came straight from the imagination of their authors…

Annie Souriau, a seismologist at the Earth and planetary dynamics laboratory in Toulouse, explains why it is still impossible to send a probe down to the centre of the Earth. What would it encounter on its way down?

Annie Souriau, a seismologist at the Earth and planetary dynamics laboratory in Toulouse, tells how scientists managed to know so precisely what is in the bowels of our planet. Event though we are in a time when human beings plan to set foot on Mars, they are not going to make a journey to the centre of the Earth for a while.

Jacques Malavieille, a geologist at the Geosciences Laboratory in Montpellier, explains the processes that lead to the formation of mountains. The Alps or the Himalayas have not always existed. How did these mountain ranges appear? How did they rise up? On Mars, some mountains exceed 20 kilometers in height while on Earth the mountain ranges do not extend beyond 9000 meters in altitude. Why is that so? This film is part of a series of 22 films entitled "Planet Earth Below the…

The historian Gabriel Gohau of the REHSEIS laboratory in Paris recounts the history of modern geology. The word geology appeared in the late 18th century. The pioneers of this discipline strove to understand the rises and retreats of the oceans or the formation of mountains. Gohau relates how the scientists of the time explained the appearance of relief on the surface of the globe. He also explains what were the clues that would lead a German meteorologist, Alfred Wegener, to conjecture…

The seismologist Annie Souriau of the laboratory Dynamique terrestre et planétaire (Earth and planet dynamics) in Toulouse answers questions about earthquake prevention. For as long as men have watched earthquakes, have they learned to anticipate these jolts? In some seismic regions, scientists have observed that the chemical composition of spring water changes before an earthquake occurs. Why not use this phenomenon to predict earthquakes? Are there any other warning signs? This film is…

The geologist Jacques Malavieille of the Geosciences Laboratory in Montpellier describes the processes that lead to the total disappearance of mountain ranges. A little over 300 million years ago, in the heart of what was to become France, stood an impressive mountain range with reliefs similar to those of the Himalayas. This has now completely disappeared. Scientists know dozens of ancient mountains that have been wiped out. This film is part of a series of 22 films entitled "Planet…

More than 4 billion years ago, our planet was very different from what it is today. What exactly did it look like? How did the Moon form? How do scientists go back so far in time? Francis Albarède, a geochemist at the Earth Sciences Laboratory in Lyon, explains.