Iridium is a substance found only in asteroids and other space objects. This graph shows the amount of Iridium found in different sediment layers of Earth. They are marked off into 17 sections representing time.

Question

Iridium Levels graph shows Iridium levels in sediment layers. Beginning at sediment layer 1, iridium levels remain between 0 and 5, jumping to a level of 23 between layers 5 and 6, and decreasing to near starting levels at layers 14 through 17.

What most likely happened in sediment layer 5?

A massive volcano erupted, causing global warming and lava flow, which in turn caused mass extinction.
More iridium was produced by space objects and dumped by local factories.
The impact of a space object led to the deposit of a layer of sediment high in iridium.
Fewer impacts lead to a drop in iridium levels and a mass extinction caused by a lack of sunshine.

Answer 1

The most likely explanation for the significant increase in iridium levels noted between sediment layers 5 and 6 is:

The impact of a space object led to the deposit of a layer of sediment high in iridium.

This conclusion is supported by the fact that iridium is a substance more commonly found in asteroids and space objects rather than on Earth. The spike in iridium levels suggests a singular event, likely an impact, that could have introduced a large amount of iridium into the Earth's sediment as a result of a space object collision.