21. when did the precambrian era end?
approximately 5.4 million years ago
approximately 2 million years ago
approximately 100,000 years ago
approximately 540 million years ago

The Precambrian era ends abot 540 million years ago.

Explanation:

The Precambrian era is the first geologic era of the Earth, it initiates from the Earth's formation (4600 million years ago) and ends at the beginning of the Cambrian era (541 million years ago). It is the longest geologic era of the Earth.  

1. loamy sand is about 80% sand with 10% clay and defined mostly by sand particles with some clay to provide structure and fertility. the sand particles are easily visible and the soil holds structure but breaks apart easily.

2. scott sand can improve his soil quality by incorporating more silt and organic matter into the soil. peat moss and organic matter can also be incorporated.