The line between night and day

The Station goes around the world in an hour and a half, which means it flies through fifty minutes of day, followed by fifty minutes of night, endlessly repeating. This means that during a seven-hour spacewalk, you may see four sunrises and sunsets. I remember holding onto a handrail on the outside of the Station, which was flying silently up the Atlantic, from south to north, and as we moved toward Europe I could see the terminator—the line between night and day—rolling up over the horizon ahead of us. The white sun sank quickly behind us in a showy flurry of orange, pink, and red horizon bands, and then we were suddenly in twilight, floating into the dark half of the world. The terminator flicked over us, and, in the deeper darkness ahead and below us, I could see a huge lit-up city, glued to the curved Earth, sliding up over the rim of the world to meet me. I could see the structure of the city, with its glowing heart, its network of roads and its halo of suburban lights fading into the dark countryside. The city was Cairo, looking beautiful and radiant. Down there, millions of people were trying to make a living, find or keep a job, provide for themselves and their families, and worrying about the future. I could cover all of them with one outstretched hand. Cairo slid under and then behind me, and more cities rolled into view over the horizon, all tacked to the outside curve of the planet surface, and all seemingly moving toward us, rather than us toward them.

— Piers Sellers

Image via APOD

Weorold

It is the strangest of all places, and there is everything in the world to learn about it. It can keep us awake and jubilant with questions for millennia ahead if we learn not to meddle and not to destroy. Our great hope is in being such a young species, thinking in language only a short while, still learning, still growing up.

Seven Wonders by Lewis Thomas, before 1983

Weorold, the Old English for 'world', is a compound of wer, 'man', and eld, 'age'.  Thomas suggests the modern world itself as the first of his seven wonders, and notes that 'world' is derived from the Indo-European root wiros, which meant 'man' (apparently, the correct spelling is wiHrós).

Image: map of space debris orbiting Earth via Reddit

Crystals as big as cities

Some believe that the boundary between the inner and the outer core [of the Earth] is undulating and mushy, with the iron crystals growing dendritically; reaching out like giant iron trees with a kind of iron mush between them. Others believe the topmost few hundred kilometres of the inner core consist of small crystals of iron, but inside the inner core they may merge, losing their individual identity as they become giant crystals aligned with the Earth’s overall magnetic field. 

These crystals are marvels, unseen wonders of the solar system. If you could sail past them they might remind you of a geological structure similar to the basalt columns of the Giant’s Causeway in County Antrim, Northern Ireland, though thousands of times longer and wider. Single iron crystals the width of a city, stretching the distance from London to Birmingham! 

But the biggest mystery is that the inner core is a newcomer. The latest calculations indicate it only appeared between 500 and 1,000 million years ago, having grown steadily from a single crystal of iron. It continues to grow at half a millimetre a year and in a billion years it may even switch off the Earth’s magnetic field.

What would you see on a journey to the centre of the Earth? by David Whitehouse

P.S.  Some strange crystals near the Earth's surface here.

Image from Mundus Subterraneus by Athanasius Kircher (1664)

Hadean

The collision of a 500km diameter body with the Earth results in a cataclysm almost unimaginable. Huge regions of the Earth's rocky surface would have been vaporised, creating a cloud of super-heated 'rock-gas', or vapors several thousand degrees in temperature. It is this vapor, in the atmosphere, which causes the entire ocean to evaporate into steam, boiling away to leave a [layer] of molten salt on the seafloor. Cooling by radiation into space would take place, but a new ocean would not rain out for at least several thousand years after the event. Such large, Texas-sized asteroids or comets could evaporate a ten thousand foot deep ocean, sterilising the surface of the Earth in the process.

from A New History of Life by Peter Ward and Joe Kirschvink (2015)

Image via Daily Galaxy