The Alvarez hypothesis is the proposal that a giant asteroid crashed into Earth, sending up dust to block out the Sun and so killed off the dinosaurs. The evidence supporting the Alvarez hypothesis is the discovery of an almost uniform layer of Iridium around the globe, say at the time of the Cretaceous-Tert iary (K/T) extinction, approx. 65 million years ago. Iridium is very heavy and on Earth it only exists in the Lower Mantle (660 to 2900 kilometers down).

Rather, Dr. Gerta Keller describes that the K/T extinction was due to an extended period of intense volcanism. Iridium was delivered to the surface via mantle plume volcanoes, which extend down into the Lower Mantle.

Volcanic emissions include steam, CO2, and massive amounts of sulfur dioxide (SO2), an acidic gas and suffocant. SO2 is heavier than air.

Plodding dinosaurs lived predominately in swampy low lands. Even predators like the T Rex roamed savannahs which were not very much above sea level. Lowland dinosaurs also had relatively weak breathing systems. The sea level atmosphere is heavier thus the dinosaurs never developed the robust pulmonary systems of the mammals. During the K/T extinction no tetrapods weighing more than 25 kilograms (55 pounds) survived.

The lowland dinosaurs choked on the SO2, defoliation set in, and acidic gases turned the oceans anoxic, killing off many marine species.

The nimble 4-footed mammals could climb up mountainsides to get away from the suffocating fumes. The winged creatures joined us in our ascent. Marmosets still live high in the Rocky Mountains.

So there you have it. Without tectonics and volcanoes, the giant predator reptiles would still be chasing our ancestors into extinction.

We are here because our ancestors could climb to safety.