If you can look into the mirror without laughter, you have no sense of humor. --Unknown - The most effective way to do it, is to do it. - Amelia Earhart -

WE DON’T KNOW WHAT THE INTERIOR OF THE EARTH LOOKS LIKE. JULES VERNE, ONE OF THE EARLY SCIENCE FICTION WRITERS, ACTUALLY HAD A BOOK CALLED “JOURNEY TO THE CENTER OF THE EARTH.” HOWEVER, IT IS STRICTLY SCIENCE FICTION. MAN HAS NEVER BEEN ABLE TO TRAVEL VERY FAR UNDERGROUND BECAUSE OF THE HIGH PRESSURES AND TEMPERATURES.

THE DEEPEST MINE IS A GOLD MINE IN SOUTH AFRICA THAT GOES TO A DEPTH OF 3.6 KM. TEMPERATURES AT THIS DEPTH ARE 55o C (131o F), BUT AIR CONDITIONING IS USED TO BRING THE TEMPERATURE TO AROUND 80o F. THE DEEPEST SCIENTIFIC DRILL REACHED 12 KILOMETERS IN RUSSIA. EARTH HAS A RADIUS OF ABOUT 6,370 KILOMETERS. THE JAPANESE HAVE A DEEP DRILLING SHIP THAT IS ATTEMPTING TO DRILL INTO THE MANTLE THROUGH THE THINER OCEANIC CRUST.

WE GET ALL OF OUR INFORMATION ABOUT THE INTERIOR STRUCTURE OF THE EARTH BY STUDYING SEISMIC WAVES. SEISMIC WAVES ARE PRESSURE WAVES THAT ARE FORMED AS A RESULT OF EARTHQUAKES. SEISMIC MONITORING STATIONS ARE LOCATED AROUND THE WORLD. THESE STATIONS CAN RECORD THE INTENSITY AND TIME WHEN THESE WAVES ARRIVE. THIS INFORMATION CAN THEN BE POOLED TO GAIN INFORMATION ABOUT THE STRUCTURE OF THE INTERIOR OF THE EARTH.

THE CRUST VARIES IN THICKNESS. THE CRUST UNDER THE OCEANS IS THINNER THAN THE CRUST UNDER THE CONTINENTS. IT AVERAGES ONLY ABOUT 7 KM IN THICKNESS AND RANGING IN THICKNESS FROM 5 TO 8 KM. IT IS MADE OUT OF DENSER MATERIAL - USUALLY BASALT (A DARK ROCK). THE CRUST UNDER CONTINENTS IS ABOUT 30 KM THICK AND AVERAGES FROM 10 TO 70 KM THICK, AND IT IS MADE UP OF MOSTLY GRANITE.

MOST OF THE UPPER MANTLE IS SOLID, LIKE THE CRUST, BUT IT IS MADE UP OF DIFFERENT TYPES OF MINERALS THAN THE CRUST. THIS BOUNDARY BETWEEN THE CRUST AND THE MANTLE IS KNOWN AS THE MOHO, WHICH IS SHORT FOR MOHOROVICIC DISCONTINUITY. THE CRUST AND THE UPPER MANTLE MAKE UP A LAYER CALLED THE LITHOSPHERE. THE LITHOSPHERE MAKES UP THE TECTONIC PLATES WHICH FLOAT AND MOVE ON THE PLASTIC PART OF THE MANTLE, THE ASTHENOSPHERE.

THE ROCKS IN THE ASTHENOSPHERE ARE CLOSE TO THEIR MELTING POINT AND ARE SOFT AND PLASTIC. THIS ZONE IS ABOUT 200 KM THICK. THE ROCKS IN THIS ZONE ARE LIKELY TO FLOW. MAGMA IS ALSO GENERATED IN THIS ZONE. THE TECTONIC PLATES THAT MAKE UP THE LITHOSPHERE FLOAT ON THIS SEMI-LIQUID ZONE.

Earthquake Map KNOWING THE BOUNDARIES OF TECTONIC PLATES IS IMPORTANT, AS THIS IS WHERE SEISMIC ACTIVITY AND VOLCANIC ACTIVITY OCCURS.

CONVECTION IN THE EARTH’S MANTLE CAUSES MOTION OF THE TECTONIC PLATES. CONVECTION MODEL

The mantle is the thick layer of hot, solid rock between the crust and the molten iron core. The mantle makes up the bulk of the Earth, accounting for two-thirds of its mass. The mantle starts about 30 kilometers down and is about 2900 kilometers thick.

AFTER THE MANTLE, YOU HAVE THE OUTER CORE, WHICH IS ABOUT 2250 KM THICK. THE OUTER CORE IS LIQUID, AND IT IS MOSTLY IRON. THE OUTER CORE IS EXTREMELY HOT, AND FLOWS AT A RATE OF SEVERAL KILOMETERS PER YEAR IN LARGE CONVECTION CURRENTS. FLOWING METAL GENERATES ELECTRIC FIELDS, WHICH, IN TURN, GENERATE MAGNETIC FIELDS. THIS IS THE SOURCE OF THE EARTH’S MAGENTIC FIELD.