Wow. Just... wow.
I knew that humans had left a large footprint on the planet, but I don't think I ever really quite grasped the scale. According to the Geological Society of America, in the February issue of GSA Today (pdf), it could be argued that we have entered into a new geologic epoch, the Anthropocene. (I say "it could be argued", because the scientific community is doing just that.) The actions of humans have had effects on a global scale--erosion due to agriculture and deforestation, changes in sediment dispersal due to both erosion and the damming of most of the significant rivers, increased carbon levels, accelerated extinctions and population declines, ocean chemistry changes, especially impacting coral reefs and plankton exoskeletons...
These changes are big enough and abrupt enough to serve as a geologic marker. A million years from now, future geologists (human or not) will be able to see our footprint. I just hope they aren't using it as a cautionary tale--"this species, unlike the dinosaurs before them, brought their end on themselves..."
The scale of geologic time is vast
With all of human history a blink—
The march of continents, the ages past
The growth of life, the ice-caps swell and shrink
To mark the boundaries at this scale, we note
Some catastrophic change within the rock—
A comet’s impact kicks up ash, to coat
The planet’s surface, and to mark our clock
We humans, in the past two hundred years,
Have changed the earth is many different ways
With mass extinctions, global warming fears,
Oceans rising, rain forests set ablaze…
We see what comes from human and machine
As Holocene becomes Anthropocene