The Grand Canyon - Then and (Almost) Now

My attention has been drawn in the last week to two articles both concerning the Grand Canyon. THIS ARTICLE was sent to me by a correspondent - thank you - and concerns well preserved fossils from the middle Cambrian (Bright Angel Formation) 505 million years old, found in the Grand Canyon, and THIS ARTICLE which suggest that the meteor impact which created Meteor Crater, 100 miles from the Grand Canyon, caused landslides which dammed the canyon. This happened 56,000 years ago - almost yesterday!

The Cambrian fossils found are slightly younger (3 million years only!) than those of the Burgess shale and are mainly priapulid worms with some crustaceans and molluscs. They show that life was innovating new forms. The source paper can be found HERE and has some wonderful pictures of the beautifully preserved (but tiny) fossils.

Crustacean sternal elements from the Bright Angel biota.

Paragnath-bearing triangles are indicated by 1 s, and the successive posterior triangles by 2 s. (A) Posterior end of paragnath-bearing triangle and anterior section of successive triangle. (B) Complete triangle with laterally splayed paragnaths (black arrows). (C) Detail of scaly ornament of median cuticular strip in (B). (D) Detail of anterior setose surface in (B). (E) Complete paragnath-bearing triangle, with articulated anterior section of successive triangle. (F) Detail of boxed area in (E) showing scale-bearing cuticular strip and marginal setal fringes. (G) Articulated paragnath-bearing and partial posterior triangles defining median food groove. (H) Detail of boxed area in (G) showing sphaeromorphic acritarch adpressed onto the food groove cuticle. (I) Subtriangular cuticular lobe, representing possible setulose labrum. (J) Complete paragnath-bearing triangle and articulated, semi-complete posterior triangle. (K) Detail of boxed area in (J) showing spheroidal acritarch adpressed onto the food groove cuticle. Slide numbers and England Finder coordinates listed in data S1. Scale bars, 50 μm except in (C) and (H) (5 μm) and (D), (F), and (K) (25 μm).

The evidence for the damming of the Grand Canyon is not controversial. There are caves 45m above the river which have driftwood logs in them. In the last few years improved dating techniques have been used and they show that the ages of the damming and the meteor impact are about the same. Whether one caused the other is rather more difficult to prove.