As @laelaps describes so vividly in her book, The Last Days of the Dinosaurs, this heat -- which only lasted a few hours--was lethal to most animals on the Earth's surface.

Most of those that survived were the ones that could hide in burrows or in the wet protection of lakes, swamps, or the oceans. And then they had to contend with a blasted, charred landscape where little plant life remained except as seeds or roots in the soil.

The survivors weren't out of the proverbial woods yet. The ash of these global fires, and the dust from the impact, then severely cooled the planet in an "impact winter" that lasted for years. Most plants lacked the light they needed to thrive. Food was scarce.

The recovery of life in the aftermath of this mass extinction is one of the greatest stories of resilience in Earth's history.

And we owe it, in part, to the humble fern.

The fossil record is like a book read in the rocks. Some pages (rock layers) are really detailed, with lots of information. Others are missing -- sometimes entire chapters. Sometimes, individual pages are really thick, and the words are blurry -- you can only make out fragments.

The K-Pg impact is not one of those blurry, thick layers where the geologic timeline is muddy.

It's one really bad afternoon recorded in a visible layer of dust, ash and charcoal. You can even touch it, in places like New Mexico, where the rock outcrops are easily accessible.

That bright line in the rock marks the end of the old world (dinosaurs, cycads and conifers) and the beginning of the new (flowering plants and mammals, which rapidly filled the niches left by dinosaurs).

No impact, no us. It's a debt we can't repay, but we can pay it forward.