Only 28% of respondents 65 and over thought there was solid evidence the earth was warming because of human activity, versus 42% overall.

WSJ: On Climate Change, Some Arguments Shift

And the earth's solid surface can be made to stand in for that of other planets, too.

ECONOMIST: Planetary pretenders

The inner core, made of very pure, solid iron, rotates along with the outer core, dragging the Earth's magnetic field with them.

BBC: Earth's wobbles reveal deep secrets

We learn why water, unlike most of the substances we run into on Earth, is denser in its liquid than in its solid form (H2O molecules are kinked rather than straight, so the space between them increases when water is quiescent).

FORBES: The Story Of Eau

The space shuttle uses ATK's four-segment solid rocket boosters (SRBs) to do the major part of lifting the shuttle stack off the Earth.

BBC: New rocket could lift astronauts