Final answer:
The primary transparent material used in greenhouse construction shown by Dr. Lieth in Columbia is glass, favored for its transparency and ability to allow sunlight to pass through, necessary for plant growth.
Step-by-step explanation:
The primary transparent material used in the construction of greenhouses, like the ones Dr. Lieth has shown in Columbia, is glass. Glass is chosen for its transparency, allowing sunlight to penetrate through, which is crucial for plant growth inside the greenhouses. Materials like soda-lime-silica glass are widely used due to their transparency and ease of formation, despite their high thermal expansion and poorer resistance to heat compared to other materials. While polycarbonate is also utilized for its unbreakable nature in many applications, it is not the primary material used in the greenhouses mentioned.