It wasn’t the actual impact that killed them, it didn’t send a fire wave across the entire planet, but it was the dust clouds that were created, it poisoned the air and messed with weather and temperature, which made it really hard for anything too big to live.

It kicked up enough material to cause a global winter and darkness that lasted two to four years, killing almost all land plants. Thus, killing most land animals bigger than the size of a rat. And killing many sea creatures, too. The sun is really important.

The impact was so large it was felt all around the world. Earthquakes of magnitude 12 were felt all around the world. That’s 1000 times more powerful than any recorded earthquake. For a few moments temperature got as hot as an oven even on the other side of the planet. 70 percent of the plants were gone in fires that day. The dust that was kicked up then blocked the sun and most plants died after a while of that. With plants dead animals all along the food chain died of starvation.

A) The majority of the effects of the asteroid impact happened locally in the Americas, but extinctions happened for months everywhere on the planet. Mostly, the impact killed off any animal that required lots of plants as food and any predator that ate those. Small animals survived because the food was scarce until around a year later, when the vegetation had grown again.

B) The effects were indeed minor in the other side of the world. The tuatara in New Zealand is essentially a non flying dinosaur that survived the impact perfectly fine.

Across the entire globe exists the K-Pg Boundary (formerly known as the KT boundary). Beneath it, one finds dino fossils. Above it, no dino fossils (specifically non-avian dinos). The actual boundary is quite visible, tons of pictures of it online. It’s a band of concentrated iridium, suggesting a massive impact event – like the Chicxulub Crater.

The immediate effects of such an impact would have resulted in earthquakes, tsunamis, firestorms (and thus forest fires) that would have immediately killed off several unsheltered surface-dwelling organisms. There’s debate about how rapidly the extinction event came about, whether there was a global fireball from an (admittedly MASSIVE) impact event or a slower event due to abrupt climate change from all the matter that a massive impact would toss into the atmosphere.

There’s two other factors to keep in mind that eludes a lot of people when discussing the K-Pg extinction: Most importantly for terrestrial (land) organisms is that all the land on the planet was more concentrated – as in all the land was closer together. Not quite Pangea, but the continents weren’t as spread out as they are today. There was also less land due to the higher temperatures of the period, hence smaller amounts of water trapped in the ice caps and glaciers, so ocean levels were higher (it’s why we sometimes find marine fossiles far inland and even on mountains!) The other thing is that there are volcanoes in modern India that were erupting *at the same time* and really delivered a one-two knockout punch for the dinos in terms of that abrupt climate change.

In short, big meteroite and big volcanoes + smaller land = dead dinos. Continental shift + geological process = dinos on “other side of the world” being dead, too.

Of course, this is our best guess. But it’s a guess that has loads of geological evidence behind it.