Saturday, May 28, 2016

Core Understanding

Flow model of Earth's liquid core
by Gary A. Glatzmaier
Earth's core generates a high magnitude magnetic field that acts as a shield deflecting lethal solar and cosmic radiation.

The invisible magnetic field extends from Earth's inner core into space.

Surprisingly little is understood about the physics of Earth's core.

"We do not understand how the Earth’s magnetic field has lasted for billions of years. We know that the Earth has had a magnetic field for most of its history. We don’t know how the Earth did that."
David Stevenson, California Institute of Technology

Planets in our solar system with weaker magnetic fields and less capacity to deflect lethal radiation (Mars and Venus), don't appear suitable to support life.

Our extra-terrestrial understanding rapidly advances because we've launched exploratory probes into space and because the universe weaves a narrative from various forms of electromagnetic radiation — principally light. Our subterranean understanding, our knowledge about the machinations of Earth's core, slowly plods along because of the physical and practical limits of sub-surface exploration.

Existential curiosity constrained by the practical limits of experiential discovery has been fodder for poets for millennia, like Charles Simic's contemplation of a stone:
From the outside the stone is a riddle:
No one knows how to answer it.
Yet within, it must be cool and quiet
Even though a cow steps on it full weight,
Even though a child throws it in a river,
The stone sinks, slow, unperturbed
To the river bottom
Where the fishes come to knock on it
And listen.
Charles Simic, excerpt from the poem Stone

All the deepest tunnels, mines, and borings are made within the confines of Earth's crust. All Earth's deepest caves and chasms exist within the crust, yet the crust is like an eggshell compared to Earth's immense interior.

If Earth were the size of an apple, one of the deepest exploratory holes (the Kola Superdeep Borehole), wouldn't pierce the skin of the apple.
"There is a danger that we will compartmentalize our understanding of an aspect of the universe by saying to ourselves, ‘OK, we know we can’t go there, so we’re going to build this elaborate story of what’s there based on remote observations.’ And this is what we do for the Earth."
David Stevenson
While exploration and direct experience are often the preferred pillars of discovery, much of scientific theory advances by posing plausible models and by forming mathematical constructs often without the aid of exploration or direct experience.

Researchers have calculated the relative age of Earth's crust compared to its core. From their calculation, they proposed that core is 2.5 years younger than its crust. Their calculation is based on a construct from the theory of relativity called time dilation.

Relativity posits that massive bodies, like planets, warp spacetime. The spacetime warp causes a gravitational pull that necessitates the slowing of time since gravity is a function of mass and acceleration (which includes a component of time). A hypothetical clock placed on the crust (larger mass) would run faster than one placed near the core (smaller mass).
"Trying to understand the way nature works involves a most terrible test of human reasoning ability. It involves subtle trickery, beautiful tightropes of logic on which one has to walk in order not to make a mistake in predicting what will happen."
Richard Feynman