Trace fossil since a trace fossil are fossilized nests, gastroliths, burrows, footprints, etc.
<span>The half-life of carbon-14 is so short that it can be used only to date materials that are less than 70,000 years old</span>
El Niño
is characterized by unusually warm ocean temperatures in the Equatorial Pacific, as opposed to La Niña, which is characterized by unusually cold ocean temperatures in the Equatorial Pacific.