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The arguments are so bitter because Gerta Keller has re-opened the case which most others considered closed.
辩论相当激烈，因为Gerta Keller又重新提起了大多数人认为已经盖棺定论的事件。
In doing so she has sparked a scientific civil war.
由此，她的行为引发了一场科学论战。
And all because she questioned the accepted theory about what wiped out the dinosaurs.
而这一切都源于她对早已公认的恐龙灭绝原因提出了质疑。
Scientists began to investigate a layer of rock formed sixty five million years ago.
科学家们开始调查6500万年前形成的岩石层。
It's seen in mines and rock outcrops around the world.
它们遍布世界各地裸露地表的矿藏和岩石中。
Below this layer there are lots of dinosaur fossils, above it there are none. It's called the KT boundary.
这个地层下面埋藏着许多恐龙化石，而它的上面却没有。这个地层被称作第三纪界线层。
This is the KT boundary, and because it's such a thin, sharp line
这就是第三纪界线层，由于它是一条窄而清晰的地层，
we know something dramatic must have happened here, some catastrophe
我们断定当时发生过一些剧烈事件，某种大灾难，
and until recently we have almost no clue what happened whatsoever here, so it remained a total mystery.
但直到最近我们都还没有发现有关真相的线索，所以它仍然还是个谜。
Then in 1979 they discovered a clue in the KT boundary.
后来在1979年，他们在第三纪界线层中发现了相关线索。
A high concentration of an element called Iridium.
极高浓度的铱元素。
Such quantities are extremely rare on earth and usually come from outer space.
这种元素在地球上极其稀少，一般都来自外太空。
So as soon as you find ten thousand times more Iridium at the very moment when the dinosaurs disappear,
我们发现铱元素浓度比平常高1000倍，而正是在这个时候恐龙消失了，
you know somewhere on earth a very big impact must have happened by an asteroid or a comet.
所以推测地球上某个地方一定发生了由小行星或彗星造成的大碰撞。
