This is the 11042nd most frequent Russian word.
гибелью
"Гибелью" means "by death" or "by ruin/destruction" in English.
"Гибелью" in this context refers to the irreversible destruction or demise of the ecosystem.
Экосистема находилась под угрозой гибели из-за загрязнения.
The ecosystem was under the threat of destruction due to pollution.
"Гибелью" is used here to signify the historical event of a civilization's decline or disappearance.
Она сожалела о гибели древних цивилизаций.
She regretted the demise of ancient civilizations.
Here, "гибелью" relates to a state or event of death or destruction, often sudden or tragic.