Center Of The Earth
Written by Jerry Coffey
Cut away of planet Earth
In the past scientists have defined the center of the Earth’s mass in two ways: either as the mass center of Earth as a single object or as the mass-center of Earth’s system, including ice sheets, oceans and our atmosphere in the equation. The reason that there are two definitions of the core is that the Earth is ever changing. "By its very nature, Earth's reference frame is moderately uncertain no matter how it is defined," said Donald Argus of NASA’s Jet Propulsion Laboratory in California. “The problem is very much akin to measuring the center of mass of a glob of Jell-O, because Earth is constantly changing shape due to tectonic and climatic forces." If Earth were a completely solid, perfectly round object, finding its center of mass would be sweet and simple. However, our planet is not perfectly round. Couple that with the fact that the Earth's mass doesn’t stay put, but instead changes over time as glaciers melt, tectonic plates move and volcanoes empty out to lay massive lava on Earth’s surface. These changes in mass atop and beneath Earth’s surface cause the center of mass to shift slightly over time.
Donald Argus has proposed a new way to measure the center of the Earth. The new center-finding technique can estimate Earth’s center of mass to within 0.04 inches a year. The center of mass is calculated as a relative measurement, and so the measurement is given as a velocity. The Earth-only reference frame will improve estimates of sea-level rise made by satellite altimeters, which rely on measurements of the location and motion of the center of mass of Earth’s system. Sea-level rise is a gauge of global warming, and so the results will boost scientists’ understanding of the increase in our planet’s average temperature.
The center of the Earth is thought to be in two parts: a solid iron inner core and a molten core surrounding that. The core was discovered in 1936 by monitoring the internal rumbles of earthquakes, which send seismic waves rippling through the planet. The waves, which are much like sound waves, are bent when they pass through layers of differing densities, just as light is bent as it enters water. By noting a wave's travel time, much can be inferred about the Earth's insides.
The Integrated Ocean Drilling Program (IODP) seeks the elusive "Moho," a boundary formally known as the Mohorovicic discontinuity. It marks the division between Earth's brittle outer crust and the hotter, softer mantle. This is one step in a series to reach the center of the Earth. The new hole, which took nearly eight weeks to drill, is the third deepest ever made into the floor of the sea, according to the National Science Foundation (NSF). The rock collection brought back to the surface is providing new information about the planet's composition. If we are gleaning new information from the upper mantle, what might we learn when we reach the center of the Earth?
There are a couple of good articles about the quest to reach the center of the Earth here and here. We have a great article about how far it is to the center of the Earth here on Universe Today. Astronomy Cast offers a good article about the plate tectonics that make measuring the Earth's core so difficult.
Filed under: Astronomy
Tags: center of the Earth, Earth, geology
