All the plants we know today descended from the same ancestor: a teeny-tiny green alga — that's the singular for algae — that existed around 500 million years ago.

我们今天所知道的所有植物都起源于同一个祖先：一种微小的绿藻——这是藻类的唯一名称——大约存在于 5 亿年前。

Researchers have not been able to find traces of the compounds in rocks older than that, despite the existence of fossils of a red and a green alga — both eukaryotes — dating back about one billion years.

尽管存在着约10亿年前的红色和绿色藻类的化石（都是真核生物），研究人员却无法在比那更古老的岩石中发现这些化合物的痕迹。