We live on a sphere of rock that is nearly 8000 miles across. A non-stop 80 miles per hour elevator ride straight down to the center of Earth and back would take over 4 days. What would you see along the way? Would it be the typical grade school book depiction of uneventful colored shells of crust, mantle, core? The short answer is “no”, there is so much more… But how do scientists know what lies beneath our feet? What kind of instruments, measurements, or analyses permit us to take that voyage into the depths of our planet? No physical device, drilling or otherwise, can go deeper than a small fraction of 1% of the way down. So how do we know what we know? And what do we not know?
In this presentation, we venture far below our familiar surface into the inner realms of our planet. Our journey will be a scientific expedition: cutting edge seismic imaging lays the foundation for updating our understanding of the interior. Combining this with numerical predictions of the slow-motion convection of Earth’s mantle rock, along with laboratory simulations of realistic deep Earth chemistries, we are now able to begin piecing together a history of the planet that not only involves the interior, but also the evolution of the surface, including plate tectonics.
Our so-called modern-day odyssey will highlight several fascinating deep Earth phenomena discovered in recent decades. For example, if our elevator ride to the center stopped around 1500 miles deep, we would witness two massive blob-like anomalies—one beneath the Pacific Ocean and the other beneath the western side of the African continent and the Atlantic Ocean. These seismically-imaged structures are 100’s of miles tall, and continental in size. They may relate to the remnants of Theia, a Mars-sized planet that collided with Earth 4.5 billion years ago to form our Moon. Traveling deeper to the base of the solid rock mantle, where it meets the fluid iron alloy outer core, we find a different “mountain range” of partially molten rock (called ultra-low velocity zones for their sluggish seismic wave speed properties). These phenomena (and others) provide important evidence for the convective motions of the deep interior that relate to formation of hot thermal plumes that extend to the surface resulting in volcanism (including Earth’s largest past volcanic eruptions). We are in an exciting time to venture beyond Jules Verne’s realm of fiction into scientific discovery—the amount of seismic data used for imaging keeps increasing, as do studies of deep Earth phenomena from a spectrum of geoscience disciplines. Computing power and tools also continue to improve. We’ll finish our journey by looking forward, and discussing how scientists can continue to sharpen the focus of interior imaging and unraveling the fascinating history of our planet.