Unit 23

UNIT 23 WORD LIST accurate If something is accurate it is completely correct. The story in the newspaper wasn't very accurate. analyze To analyze something is to study it. The scientist will analyze the blood sample, asteroid An asteroid is a giant rock from outer space. In 1908, a giant asteroid hit Siberia. controversy A controversy is a dispute about something that affects many people. There has been a lot of controversy over the judge's decision. evolve To evolve is to change over time. Many people think that humans evolved from animals. factor A factor is something that has an effect on the way another thing happens. Smoking is the main factor that causes lung cancer. genetic If something is genetic, it is related to the genes in one's body. The color of one's eyes is genetic. genome A genome is the collection of all the genes in a living thing. Understanding the human genome may help cure many diseases. identical To be identical is to be the same as someone or something else. James and John are identical twins. intellectual An intellectual is a very smart person. We've always considered my Uncle Max to be the intellectual of the family.

majority A majority of something is more than half of the people or things in that group. A majority of the people voted for Tom Smith in the election. mammal A mammal is an animal that usually has hair and is not born from an egg. Even though they live in water whales are actually mammals. multiply To multiply is to increase in number. In the past year, the number of people at work has multiplied by ten percent. offspring Offspring are the children of a person or the babies of an animal. The dog's offspring had the same color of fur as she did. pesticide A pesticide is a substance used to kill insects. The farmer sprayed his crops with a pesticide to keep bugs away. regulate To regulate something is to control how it happens. The bank regulates how much money people can borrow. reinforce To reinforce something is to make it stronger. Peter reinforced his opinion with information from a book. stricken If someone or something is stricken by a disease or problem, they are badly affected by it. The pilot landed the stricken airplane with difficulty. vast If something is vast, it is very large. The wealthy man bought a vast amount of land in the countryside. vegetarian A vegetarian is someone who does not eat any meat products. I became a vegetarian because I don't like the taste of meat.

How the Dinosaurs Really Died Many scientists and intellectuals think that dinosaurs died when an asteroid smashed into the Earth millions of years ago. However, recently, there has been some controversy over this theory. Some scientists think that it isn't accurate. They think that a tiny insect may have been the biggest factor in the death of these huge creatures. That insect was the mosquito. These scientists do think that an asteroid hit the Earth in the time of the dinosaurs. But that wasn't what killed all of them. At that time, insects, including the mosquito, were beginning to evolve. Today, we can regulate the number of mosquitoes with pesticides. But that was impossible millions of years ago. The mosquitoes multiplied quickly. And they were certainly not idle. Since there were so many mosquitoes, it was easy for them to bite many of the dinosaurs. When they bit another living thing, the mosquitoes passed along a deadly disease. So the dinosaurs were stricken with the disease. The vast majority of them—from the vegetarians to the meat eaters died. To reinforce this idea, scientists stress how gradually the dinosaurs died. If an asteroid had killed them, they would have died very quickly. But the number of dinosaurs decreased slowly. In addition, scientists have found genetic material of mosquitoes in fossils. This material proves that mosquitoes existed back then. Although there may have been other factors, the dinosaurs died mainly because of disease, the scientists say. No matter how it happened, the dinosaurs' death had a major impact on other living things. Many dinosaurs ate mammals. After the dinosaurs died, mammals were able to evolve and produce offspring. Birds also evolved. Scientists have analyzed the genomes of birds and have discovered that birds have identical genetic material to some dinosaurs. So, there may still be dinosaurs among us after all.