When a scientist researched the clay layer in the Late Cretaceous strata in the Gubbio region of Italy, he found that the content of trace element iridium has increased sharply by 30 to 160 times compared with strata in other periods. Samples from many locations around the world have found the same. Conclusion: The abnormally high iridium content in the formation in the late Cretaceous is indeed universal. Based on this, scientists have speculated that a huge asteroid hit the earth in the late Cretaceous, and the dust generated by the sky covered the sky, causing a huge change in the surface climate Which led to the demise of dinosaurs. Which of the following, if true, would most weaken the scientists' speculation? ['A asteroid is generally composed of silicon and iron elements. Huge asteroids land on the surface of the earth. Even after a long period of time, it is impossible to disappear.', 'Most of the rock formations in the late Cretaceous period are igneous rocks formed by lava cooling, while sedimentary rocks accumulated by the dust generated by the asteroid impacting the earth occupy only a small part of the surface.', 'Ciridium exists not only in celestial bodies outside the earth, but also in the crust.', 'The dinosaurs and dinosaur egg fossils that have been found all exist in the stratum below the clay layer rich in iridium.']