得知地球上每年有几百种植物消失时,我们大家都非常震惊.(SHOCK)

Knowing that hundreds of plant species extint annually on earth, all of us were shocked.

[说明]
物种消失用extint；属于前置状语结构，用动名词可以表达；后面的主句应该是过去时态；每年annually．

Learned that hundreds of plant species disappear every year on Earth, we are all very shocked