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


Saturday, May 21, 2016

Oxygen-Rich Atmosophere

Hundreds of species of bacteria, unicellular protists and deep-sea worms evolved to exist without oxygen. Most multicellular metazoa however, with rare exception, require oxygen.
"Oxygen flooded into the atmosphere as a pollutant, even a poison, until natural selection shaped living things to thrive on the stuff and, indeed, suffocate without it." Richard Dawkins
Oxygen is produced as a byproduct of photosynthesis. Microbes in the oceans produce half of Earth's atmospheric oxygen. Macro algae, like kelp, and land plants provide the remainder.
"...the life of the planet began the long, slow process of modulating and regulating the physical conditions of the planet. The oxygen in today's atmosphere is almost entirely the result of photosynthetic living, which had its start with the appearance of blue-green algae among the microorganisms."Lewis Thomas

View of the crescent moon through the top of the Earth's atmosphere
by NASA Earth Observatory

About 20 percent of the atmosphere consists of free molecular oxygen O2 not bound to another element like atmospheric gases carbon dioxide and sulfur dioxide. Much of Earth's total oxygen is sequestered in oxides in rocks buried deep in Earth's interior.

How did Earth's initially oxygen-free atmosphere change to its oxygen-rich state?

Geological, isotopic, and chemical evidence suggest a Great Oxidation Event occurred about 2.3 billion years ago, although the actual causes remain contested and inconclusive.

A multidisciplinary team of researchers recently published findings that suggest the rise of atmospheric oxygen that occurred during the Great Oxidation Event, then again roughly 2 billion years later during deep-ocean oxygenation that coincided with the rise of animal life, resulted from the growth of continents in the presence of carbon life forms.

In Two-step rise of atmospheric oxygen linked to the growth of continents, the authors propose that the initiation of plate tectonics lead to a change in the composition of Earth's crust that, in turn, decreased the oxidative efficiency of Earth's surface, thus allowing molecular oxygen from photosynthesis to accumulate in the atmosphere:
In the first stage, the change in composition of Earth's crust from iron- and magnesium-rich mafic rocks to feldspar- and quartz-rich felsic rocks could have caused a decrease in the oxidative efficiency of the Earth's surface, allowing atmospheric O2 to rise. Over the next billion years, as carbon steadily accumulated on the continents, metamorphic and magmatic reactions within this growing continental carbon reservoir facilitated a gradual increase in the total long-term input of CO2 to the ocean–atmosphere system. Given that O2 is produced during organic carbon burial, the increased CO2 input may have triggered a second rise in O2. A two-step rise in atmospheric O2 may therefore be a natural consequence of plate tectonics, continent formation and the growth of a crustal carbon reservoir.
Two-step rise of atmospheric oxygen linked to the growth of continents


Saturday, May 14, 2016

Bringing Heat

Greenhouse gases trap heat in the atmosphere by absorbing it. Without greenhouse gases, the mean temperature on Earth's surface would be 0°F rather than 59°F.

Over a century of mean temperature data plotted over time demonstrates the increasing rate of the rise.
The pace of change is immediately obvious, especially over the past few decades.
Ed Hawkins
by Ed Hawkins, National Centre for Atmospheric Science

Humans have spiked a 40% increase in the atmospheric carbon dioxide concentration since 1750, the approximate outset of the industrial revolution.

Water vapor, carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbons are the greenhouse gases in order of abundance in the atmosphere. The anthropogenic spike in greenhouse gases comes primarily from human activities (power generation, transportation, and industrial agriculture).
“Thus human beings are now carrying out a large scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future. Within a few centuries we are returning to the atmosphere and oceans the concentrated organic carbon stored in sedimentary rocks over hundreds of millions of years.”
Bill McKibben


Saturday, May 7, 2016

Obligate Seeders

Fort McMurray wildfires
Smoke travelled 1130 miles overnight from the Fort McMurray wildfires, drifted into the window before daybreak, bringing the scent of burning pitch.

In Chinese cosmology, Yin and Yang is a metaphorical construct of opposing but complimentary forces. The continuous joining and separation of Yin and Yang regulates the rise and disappearance of all entities and phenomena in the cosmos.

A theme in the poem Fire Flowers by E. Pauline Johnson, first printed in a Canadian newspaper in December 1894, is that from desolation comes renewal.

The poet's personified purple-headed wild flowers emerge from the desolation of fire. Life revives. Life's resilience is its wonder.

If Yin is the tender green shoot, then Yang is the fire's heat that melted its seed coat.

In apparent cyclical perpetuity, death is the catalyst. Plants with fire-activated seed coats germinate and grow soon after the fire recedes. Such plants are called obligate seeders.

Elk Bath
A wildfire in the Bitterroot National Forest
by John McColgan

Obligate means to oblige, compel or commit, which are actions with an implied interdependence like the continuous joining and separation of Yin and Yang. In a analogous way, all living things become obligate seeders.