Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co.
The evidence that a large asteroid or comet struck the Earth at that time came from detailed studies of the thin clay layer that globally marks the stratigraphic boundary between the Cretaceous and Tertiary (K-T) geological periods.
This layer is enriched in the siderophile elements (such as iridium), indicating that the clay represents a mixture of normal crustal rocks, which typically have low siderophile-element abundances, and a small percentage of extraterrestrial material.
All the bodies in our solar system have been heavily bombarded by meteoroids throughout their history.
Uranium is a chemical element with symbol U and atomic number 92.
The fulvic acids reduced the cadmium toxicity by about the same amount as humic acids, from 4.4 to 18.6 µmol/L, but they had no effect on copper toxicity.