Most scientists agree that dinosaurs became extinct after a huge asteroid (space rock) struck the Earth. Now, an international team of researchers thinks they can show exactly why the asteroid caused dinosaurs died out.
Dinosaurs lived on the Earth for more than 160 million years. There were more than 1,000 species of land-based dinosaurs, living all over the world. But the dinosaurs disappeared very suddenly about 66 million years ago, soon after the asteroid hit the Earth. Scientists call this a “mass extinction,” which means many species died out in a very short time.
The researchers wanted to understand better why this happened. They studied all of the information that had been gathered over the past 20 years on climate change, sea levels and volcanoes in the late Cretaceous period – the time just before the asteroid struck the Earth.
They also looked at dinosaur “biodiversity” for that period. Biodiversity is the number of different species of animals or plants living in an area at one time.
By studying fossils, the researchers discovered that the populations of large herbivores (plant-eating dinosaurs like triceratops, duck-bills and ankylosaurus) had gotten much smaller by the late Cretaceous period.
The researchers do not think that the dinosaurs were slowly dying off. Animal populations sometimes get bigger or smaller naturally for awhile, and eventually go back to their usual size. The number of plant-eating dinosaurs probably would have increased again if the asteroid had not hit the Earth.
But the researchers do think that the smaller number of herbivores combined with the effects of the asteroid was what caused the mass extinction of dinosaurs.
When the asteroid struck, it caused big changes on the Earth. It left a crater about 200 kilometres wide in the area that is now Mexico. The impact caused tsunamis (huge waves) in the oceans and earthquakes around the world.
Fires started near the crater. Gases were released into the atmosphere, causing cooler temperatures and acid rain. A huge cloud of dust filled the air, blocking out the sun’s light and warmth and causing many plants to die.
Fewer plants meant there was less food for plant-eating dinosaurs. Because there were already fewer herbivores, the lack of food caused them to die off quickly.
This led to what the researchers call “cascading extinctions.” That means that, as dinosaurs at the bottom of the food chain died out, the dinosaurs that preyed on them also became extinct. The effects were felt all the way up the food chain, to the largest meat-eating dinosaurs.
The asteroid impact wiped out about 80 per cent of the species living on Earth in the late Cretaceous period. Mammals were also affected – especially larger species, or those that had specialized diets. But those that survived began to increase and spread rapidly after dinosaurs became extinct. More species emerged, until eventually mammals became the dominant animals on Earth.
Steve Brusanette, a paleontologist at Edinburgh University in Scotland, was one of the researchers involved in the study. He believes that if the asteroid had hit a few million years earlier or later, when the plant-eating dinosaur population was at a normal level, the dinosaurs probably would not have gone extinct.
If that had happened, says Brusanette, mammals would not have had the chance to thrive and evolve the way they did, and humans might not even exist.
CURRICULUM CONNECTIONS
By Jonathan Tilly
Writing/Discussion Prompt
Today’s article ends by pointing out that the end of the dinosaurs may have allowed for human existence? Science often demonstrates how the phenomena of our world are all connected, even if it’s not always easy to see right away.
Can you name two things that don’t seem onnectd, but are in fact dependent on each other?
Reading Prompt: Reading Unfamiliar Words
Using the meaning of the sentence to help understand unfamiliar words is a really powerful comprehension strategy.
Reread today’s article and underline the unfamiliar words. Ask yourself how you created meaning of these words and each time you used the sentence meaning as a strategy, draw a smiley face.
Primary, Junior, & Intermediate
Predict the meaning of and rapidly solve unfamiliar words using different types of cues, including: syntactic (language structure) cues (e.g., word order, language patterns, punctuation) (OME, Reading: 3.2).
Language Feature: Final punctuation & quotation marks
Many students are unsure where to place final punctuation marks when finish a sentence with a quotation. The rule is simple: final punctuation, like a period, exclamation mark, or question mark, all go inside the final quotation mark. Take a peek at the example below,
This led to what the researchers call “cascading extinctions.”
Write 3 sentences, each ending with a quote and a different final punctuation mark to help you remember the order of this punctuation.
