Copyright © 2007 Dorling Kindersley
About 65 million years ago, at the end of the Cretaceous Period, the Earth was affected by major changes to its environment. Animal and plant life were plunged into danger. It may only have taken one of these changes to affect life on Earth, or perhaps it was a combination of several. Whichever is the case, one thing is certain: dinosaurs became extinct at this time. Many theories exist to explain how dinosaurs died out.
In the 1990s a meteorite crater 180 km (110 miles) across, on the seabed off the Yucatán Peninsula, Mexico, was dated to the late Cretaceous Period. The rock that made the Chicxulub crater was 10 km (6 miles) across. The impact may have made so much dust that the Sun’s light was blotted out, leading to a mass extinction.
Earth is continually bombarded by debris from space, from specks of dust to lumps of rock. Most burn up as they pass through Earth’s atmosphere, but some are big enough to survive. Space rocks that land on the Earth’s surface are called meteorites. Did a large meteorite slam into the Earth, causing massive disruption that led to the death of the dinosaurs?
Towards the end of the Cretaceous Period there were many volcanic eruptions in what is now central India. They were on a vast scale, blasting huge amounts of dust into Earth’s atmosphere, where high winds blew them around the planet. As with the meteorite impact theory, this theory also says that atmospheric dust blotted out sunlight, sending the world into many years of cold and dark. With no sunlight, plants could not grow. With no food, animals starved and died.
If a giant meteorite had splashed into the sea, it would have created a tsunami – a massive wave. Had it exploded on land, it would have made a shockwave big enough to trigger earthquakes and undersea landslides which could have unleashed megawaves. They would have raced at great speed towards land all around the globe. Within a few hours the waves might have pounded low-lying land, destroying habitats and disrupting Earth’s plant and animal life.
As well as blasting dust into the atmosphere, volcanoes also create carbon dioxide – a poisonous gas that causes global warming. This extinction theory says that the rising levels of carbon dioxide caused a climate change known as the “greenhouse effect”. Carbon dioxide prevented the Sun’s heat from escaping back into space, so Earth’s climate became hotter. Water evaporated. Plants withered and died. As animals lost their food sources, they died, too.
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