SORU: aşağıdaki parçaya göre cevaplayınız
We understand from the passage that, by the time of the Tertiary period, ----.
In 1980, the physicist Luís Alvarez and his son
Walter advanced a startling theory about the demise
of the dinosaurs: that it was caused by forces that
came from beyond this world. They hypothesized
that perhaps a meteor impact had ended the age of
the dinosaurs. The primary evidence was that in soil
core samples taken in locations around the globe,
iridium, a substance very rare on Earth but prevalent
on asteroids, had been found in a thin layer of clay
separating the fossil-rich rock of the late Cretaceous
period (the end of the dinosaur age) and the sparsely
fossiled rock of the Tertiary period that followed. The
Alvarezes hypothesized that a very large
extraterrestrial object had slammed into the planet,
sending an enormous fireball into the stratosphere,
along with vast amounts of debris. A great cloud of
dust enshrouded Earth, blocking sunlight for months,
even years, and plants and animals perished in the
ensuing cold and dark. When the dust finally settled
back to Earth, it formed the telltale worldwide layer of
iridium in the clay. The scientific world was not
impressed by the theory. Indeed, some scientists
scoffed at the Alvarezes' hypothesis, but in 1990
scientists realized that a crater of 112 miles in
diametre in Mexico and dated at 65 million years old
might be evidence that the dinosaurs had indeed
died out due to the effects of a giant meteor.