We know intellectually that Earth orbits in space, but as we go about our daily lives it is easy and natural to ignore that basic fact, caught up as we are in our immediate, myopic perceptions.

Viscerally, we think of space as "out there" -- disconnected from us, of no personal consequence. Then an event occurs, like the Nisqually earthquake that shook the Puget Sound, Washington last week, to remind us that our human affairs are deeply and permanently enmeshed in a universe in which our planet is a small mote.

Though the Nisqually earthquake, named after the river delta near the epicenter, caused considerable damage, no lives were lost. That earthquake followed on the second recent seismic event in El Salvador, one in India, one in Turkey and a host of others in the past that were far more devastating to human life and property. These earthquakes remind us that the apparently solid earth beneath our feet is, on geological time scales, a shifting layer of bedrock floating on Earth's molten core.

The powerful nature of these ineluctable processes easily overwhelms human enterprise. Earthquakes remind us of the plastic character of our planet -- the storage and release of immense energy, of which we are usually blissfully unaware as we pursue our lives, our loves, our professions, our daily concerns. But the connection with the universe "out there" is even more direct, far-reaching and profound.

Our Sun and its swarm of planets formed about 4.6 billion years ago in an already ancient galaxy.

The heavy elements that make up of rocky planets, as well as the elements necessary for life on (at least) one of those planets, were forged in mighty supernova explosions. Furthermore, there is evidence the gaseous nebula that formed our proto-sun was seeded by a single nearby explosion. Among the elements ejected by supernovae are some that are unstable and subject to radioactive decay, but with very long decay times: uranium 235 (half-life of 0.7 billion years); potassium 40 (half-life of 1.4 billion years); uranium 238 (half-life of 4.5 billion years) and thorium 232 (half-life of 14 billion years). These elements were trapped in the gas that formed the Sun and planets. They were concentrated in the core of Earth by processes of settling and differentiation when the core of the young Earth was molten from the heat of impact of the planetoids from which it formed.

Eons since, the impacts have dropped off, but the long-lived unstable elements -- potassium, uranium, thorium -- continue to decay. Those decays, atom by atom, yield the heat that maintains the molten state of Earth's core. The continental plates float on that core, shifting and colliding, energizing the "ring of fire" around the Pacific basin, wherein lie the Puget Sound and El Salvador. Other plates collide to lift the Himalayas and leave treacherous ground in India, Turkey and elsewhere.

Thus the disaster that befell Seattle and Olympia, Washington last week can be directly traced to the radioactive elements spewed out by past supernovae, perhaps to a single event involved in the birth of the solar system. It is likely that a single supernova shook Seattle; it just took 4.6 billion years to do so.

The galactic game plays out over billions of years, but it shapes our planet and is manifest in 40 seconds of unstable Earth that directly and terrifyingly affects human lives. In Carl Sagan's famous phrase, "we are made of star stuff." So is Earth. The Nisqually earthquake reminds us that we do not live an isolated life on this pleasant planet, but that we are intimately connected to the galactic ecology that both grinds exceeding slow and can alter lives in a heartbeat.