It's because lipids are so tough, they can get preserved in sediment and last the hundreds of millions of years necessary, and be extracted and tell us who was there.
这是因为油脂太粗糙了，它们可以通过沉淀物保存下来， 然后经过上百亿年， 被提取出来，还能告诉我们谁曾经在那儿生存过。