Rickster, I really don't understand your point of looking all the way back to the 4.5 billion years history of the earth. If you look way back in time what we are seeing now is only ripples on the surface ....
In the early days, the earth was literally bombarded with asteroid hits, comets, all kinds of nasty things that rippled and shattered the planet to its core; Extremely violent, but a necessity. Some of these hits gave us water, all the water on the oceans come from these external sources.... This was a hard time to the planet, but a necessity for life as we know it.
250 million years ago, the earth was shattered by a volcano that was active for one million years. this eruption, called the Siberian Traps, killed 90% of the life on earth, the climate changes and consequences from this event alone is probably beyond comprehension. It took 30 million years for life to get more or less back to normal after this, and we do still have late consequences from this event... like significant amounts of methane in the atmosphere. It's suggested that the Siberian traps was triggered by an extremely big asteroid or meteor impact, but no proof of this has been shown.
65 million years ago the dinosaurs were wiped out by a meteorite impact that changed the environment to an extent that life ceased for the dinosaurs.
I believe there have been proven to be hypernovas in some galaxies that in a flash of a second releases so much energy that they may wipe out any life throughout a significant part of a galaxy, I have read that statistically this will happen every two billion years...
I do suggest that what we are seeing now is insignificant compared to some events through the history of earth, but what we are seeing now may be significant enough that the environment may subsequently change so much that we may make it extremely uncomfortable for ourselves.
The references to the earth's history is insignificant, if you ask me, we must look at what to do now.
Life will go on, the earth will go on .... There are voices claiming that we may make the human race extinct if we go on the way we do, maybe this is a reasonable thinking .... At the least, I believe that we will make it a really uncomfortable place to live if we don't stop these things ....