Transcript: Earth’s atmosphere is unique within the solar system mostly because of the nitrogen and oxygen that form the bulk of the Earth’s atmosphere: 75 percent nitrogen, 20 percent oxygen, plus carbon dioxide, argon, water vapor and other trace gasses. The weather on the Earth is generated in the lowest part of the atmosphere, called the troposphere, at a distance of up to 10 miles from the Earth's surface or 50,000 feet. The Earth's weather is caused primarily by convection patterns,...

Transcript: The ancient Greeks knew about loadstones. These were curtain rocks which, when suspended in a fluid, would appear to line themselves in response to a mysterious force. That mysterious force was magnetism, first understood through the experimentation of the physicist Michael Faraday. Now we understand magnetism very well. We understand that the Earth has a magnetic field. The north pole of the Earth's relatively strong magnetic field is not perfectly aligned with the...

Transcript: Cratering affects the evolution of planets. The cratering history of the Earth has varied over its history. Cratering was much stronger in the first half billion years when there was plenty of debris left over from the formation of the solar system. When you look at the Moon we are looking at a mirror for the cosmic environment of the Earth. The Moon shows evidence of many craters. The Earth has apparently very few. The difference is clear. The Moon is not massive enough to...

Transcript: Earth is continually sculpted by erosion. Erosion refers to all processes generally caused by wind, rain, and moving water that break down rocks and transport them across the surface of the planet. Erosion has a major effect on the way the Earth looks. Tectonic forces can raise up a mountain chain in barely 100 million years, but erosion can destroy a mountain chain in about the same time. Erosion is assisted by gravity, gravity causing erosion to move material generally from...

Transcript: The convective motions of the liquid and semi-liquid rock deep within the Earth create enormous stresses on the lithospheric rock that sits just under the crust. The lithosphere is not entirely solid, and it's not entirely liquid. You can consider it like a material like putty, where if you pull it slowly it will stretch and deform; if you pull it quickly it might break. Stresses on the lithosphere sometimes cause it to break or fracture. The result is an earthquake. Places...

Transcript: The Earth is a geologically active place driven by energy release from radioactive decay deep in the interior of the Earth. If you look at a map of the location of earthquakes and volcanoes, they trace out the geological plates exactly. For example, volcanoes and earthquakes can be traced down the western coast of North and South America, across to the Asian continent, down the coast of Japan to Southeast Asia, and then across to New Zealand. This is the Pacific Plate. At the...

Transcript: Every child who's stared at a map of the Earth has noticed that the continents seem to fit together like pieces of a jigsaw puzzle. Could this just be chance that they look this way? For many years scientists did not know. In the early 1900's German geophysicist Alfred Wegener speculated that the continents had drifted over a long period of time to their present positions. This was an outrageous hypothesis at the time. Nobody could understand possibly how continent size...

Transcript: There are three basic types of rocks found on the Earth. The first are called igneous rocks. These form from molten material that is cooled and solidified. They are very common in the rocks of the Earth's surface. Granite and basalt are two examples. Earth is a restless place, and the second major type is called sedimentary rocks. You might think that wind, sun, and rain can have little effect on something as hard as a rock, but acting over millions of years, erosion can...

Transcript: The rocks of the Earth that we are most familiar with are those right at the surface of the crust. The deepest mine we’ve every drilled on the Earth is only about 10 or 12 kilometers deep, doesn't even penetrate half the thickness of the crust. Occasionally rocks from deeper down are brought to the surface of the Earth by convection or uplifting processes. Most of the common low density minerals found in the crust are called feldspar, which is a form of molten lava that’s...

Transcript: The earth has a number of layers, and its structure changes quite dramatically from the surface to the core. The top layer is the rocky outer crust, about 30 kilometers thick. Underneath the crust is the lithosphere, a semi-liquid rock layer that the crust floats on. Below that is the thick mantle mostly made of rocks containing silicon and oxygen. Inside that is the outer core, a liquid region of high pressure, high temperature iron and nickel. At the very interior is the...

Transcript: Radioactivity is the process by which we've estimated the age of the Earth. It's also crucial in understanding how the Earth works and the source of geological activity. The interior rocks of the Earth contain small concentrations of radioactive elements or compounds. The radioactive decay process releases energy in the forms of particles and radiation. This energy suffuses through the rock and melts the rock driving geological activity. In any sufficiently massive planet,...

Transcript: With the radioactive decay process we can make an estimate for the age of the Earth. However it's a difficult technique to apply reliably. The technique only works if the parent and daughter atoms in the decay from one element to another or to an isotope are trapped in the same location. So really radioactive decay only works as an age estimate after the last time that a rock solidified. So we need to find rocks that are very old and have not melted or re-solidified. Such...

Transcript: The age of the Earth is estimated via the fundamental physical process of radioactive decay. It's possible to measure the age of things on the Earth by, say, counting tree rings, but the oldest ages are only several thousand years. Geologists can use the sedimentation record of rock and ice to estimate ages, but the Earth is a restless place having resurfaced itself every hundred million years or so through out its history. So it's hard to measure ages in more than millions of...

Transcript: Radioactive carbon dating is the way we measure the age of formerly living things. Every living thing takes in carbon either in the food that it eats or absorbing it from the carbon dioxide in the atmosphere. Most of the carbon from the atmosphere is in the stable form carbon-12, but one in a million molecules of carbon in the atmosphere involve carbon-14, the radioactive form. The radioactive form of carbon, carbon-14, decays with a half-life of 5700 years to nitrogen-14. ...

Transcript: The physical process of radioactivity was discovered accidentally in the late nineteenth century by French physicist Antoine Becquerel. He had left some uranium bearing minerals near a photographic plate in a drawer in his laboratory and came back to find the plate fogged, indicating that particles or emissions had gone from the radioactive material to the photographic plate. Radioactivity involves the decay spontaneously of an element to another form, either a form of the same...

Transcript: Earth, the third planet out from the Sun, is a special place. We live here, and Earth is still the only place known in the universe to harbor life. Related to that is the fact that Earth is the only planet in the solar system with an oxygen-rich atmosphere. It’s the largest and densest of the inner terrestrial planets, about nine thousand miles in diameter, a smooth sphere. If you could shrink the Earth down to the size of a billiard ball, it would feel as smooth as a billiard...

Transcript: Some of the general principals that relate planets to each other are to do with planetary geology. For example, larger planets are more likely to have internal geological activity than smaller planets. This is simply due to the increased mass of a planet increasing the amount of pressure in its interior and increasing the amount of energy released from radioactive elements deep within the core. These radioactive decay processes release heat which melts the interior material...

Transcript: One of the most exciting things about exploration of the solar system with spacecraft in the last few decades is the discovery that many of the objects in the solar system have their own peculiar characteristics that make them very interesting to study. It's as if some of the moons and planets have their own personalities that we can learn through their physical properties. Regardless of these distinctive features, one of the most important things to remember when studying the...

Transcript: Albert Einstein was the most famous scientist of the twentieth century and perhaps of all time. The man who invented the theories of special and general relativity was an unconventional scientist who spent most of his career outside the mainstream. His Greek teacher at high school famously said, “Einstein will never amount to much.” Einstein failed his college entrance exams twice and was only able to get admission to a teachers’ college. Eventually he worked in the Berne...

Transcript: In the physics of Isaac Newton, time and space are linear and absolute. Einstein’s theories of relativity changed forever our notions of time and space. In Einstein's special theory of relativity the equivalence of mass and energy and the idea that the speed of light is a fundamental constant means that time and space must be supple. Time can slow down due to high speed travel near the velocity of light. Masses can increase, and physical lengths can actually contract. These...

Transcript: One of the most important effects of the general theory of relativity is the fact that mass or gravity can bend light or electromagnetic radiation. To see this, consider again the example of a sealed elevator. If the elevator was in free space being accelerated and you stood in the elevator and shined a flashlight across the elevator, you can see that as light traveled across the elevator it would be deflected downwards by a tiny amount caused by the motion of the elevator...

Transcript: Einstein's general theory of relativity is based on his assertion that there's no way to distinguish between acceleration due to gravity and acceleration due to any other force. Consider the following situation: you're in a sealed and closed elevator with no way to see outside. In one situation the elevator is stationary on the Earth's surface, and you feel your normal gravity which would cause an acceleration of 9.8 meters per second per second if you dropped an object in the...

Transcript: It seems as if there are two fundamental ways of thinking about mass. One is inertial mass, the resistance an object presents to any change in its motion. Imagine trying to push a heavy object across a smooth surface. The other is gravitational mass, the force downward on an object caused by gravity. By the time of Einstein these two masses had been found to be utterly equivalent within the limits of measurement to one part in 1015 or less. To Einstein this could not be a...