Close your eyes and picture "nature." What do you see?

That would take lifetimes to explore, because nature means the full sum of creation, from the Big Bang to the whole shebang. It includes: Spring moving north at about 13 miles a day; afternoon tea and cookies; snow forts; pepper-pot stew; pink sand and confetti-colored cottages; moths with fake eyes on their hind wings; pogo-hopping sparrows; blushing octopuses; scientists bloodhounding the truth; memory's wobbling aspic; the harvest moon rising like slow thunder; fat rainbows beneath spongy clouds; tiny tassels of worry on a summer day; the night sky's distant leak of suns; an aging father's voice so husky it could pull a sled; the courtship pantomimes of cardinals whistling in the spring with "what cheer, what cheer, what cheer!"

Nature surrounds, permeates, effervesces in and includes us. At the end of our days, it deranges and disassembles us like old toys banished to the basement. There, once living beings, we return to our nonliving elements, but we still and forever remain a part of nature. Not everyone agrees with me. Many people harbor an us-against-them mentality in which nature is the enemy and the kingdom of animals doesn't really include us. Then we can attribute to animals all the things about ourselves that we can't stand.

Each day, I wake startled to be alive on a planet packed with so much life. No gasp of sunlight goes unused. Life homesteads every pore and crevice, including deep dark ocean trenches. Life's rule seems to be variations on every possible theme: And so we have tree frogs with sticky feet, marsupial frogs, poisonous frogs, toe-tapping frogs, frogs that go peep and many more.

The leafy green abundance we usually think of as nature began with Earth's earliest life-forms, blue-green algae. Their gift was the cell, a microscopic circus that still is that basis of a cougar, bombardier beetle and one's nephew. Their genius was inventing photosynthesis. Around 2.4 billion years ago, they began building solar power plants under their walls, digesting their surroundings and, in the process, excreting oxygen, a poisonous gas.

Over time, the algae sheathed the planet, and oxygen fizzed through the oceans, saturating them. Then the bubbles rose, breathing life into a slaggy sky, whose cloudbanks thinned as the blues appeared. Hydrogen ballooned away into space, while heavier oxygen stayed home. Earth became a planet rich in poisonous, flammable oxygen.

Meanwhile, evolution tinkered with creatures immune to oxygen, including some willing to pool their DNA. Complex animals evolved. And the rest is history.

In every flake of skin, we still resemble those one-celled pioneers. If they didn't excrete oxygen, we wouldn't be here. So, no matter how politely one puts it, we owe our existence to the flatulence of blue-green algae.

That should humble us and remind us that we share our origins and future with the rest of life on Earth.

We need a healthy environment if we hope to stay healthy.