그 기간 동안 칼슘과 철, 그리고 실리콘이 환경에서 늘어나게 되었습니다. 생물들은 이 단단한 물질들을 사용하는 법을 배웠죠.
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.