And it was during this time that there was increased calcium and iron and silicon in the environment, and organisms learned how to make hard materials.
그 기간 동안 칼슘과 철, 그리고 실리콘이 환경에서 늘어나게 되었습니다. 생물들은 이 단단한 물질들을 사용하는 법을 배웠죠.