# The Origin of Time

Author: A.G. Smith
Publisher:
Publish Date: 2006-05-01
Features: Scholars with a thirst for knowledge have long been curious about the age of the Earth and the life that has existed on it, continuously exploring. In 450 BC, the Greek historian Herodotus discovered fossils of marine bivalves in the Libyan Desert, which baffled people because bivalve animals cannot live on land. Herodotus concluded that this desert might have been the seabed of the Mediterranean in the past. Since many of the species in the fossils had gone extinct, Herodotus posed another question: How long ago did these marine bivalves live? Later, religious authorities believed that the fossil record preserved traces of animals and plants that existed before the Great Flood. Some people argued that, according to the Bible, God created the heavens and the Earth on October 23, 4004 BC, Sunday. However, many were not convinced by this explanation. In the 19th century, Europeans began to study rock layers (also called strata). They found that different types of fossils existed in each layer of rock. Their conclusion was that different rock layers and the fossils they contained formed in different eras. Due to the numerous layers of rock, they believed that the Earth was much older than people had imagined. In the Arctic, people discovered fossils of tropical plants; in Brazil, they found remnants of the ice age. These discoveries proved that the Earth had undergone tremendous changes over vast periods of time. In 1858, Darwin published On the Origin of Species, in which he explained the changes of the Earth. Darwin's theory proposed that the Earth existed in the universe much earlier than people had thought, millions of years earlier. Around 1900, the discovery of radioactivity provided geologists with a more precise method for determining the age of the Earth. How do geologists use radioactivity to calculate time? In nature, there are many naturally occurring radioactive elements, such as radium and uranium, which decay at a fixed rate, eventually turning into lead. Geologists can determine the age of rocks by measuring the amount of uranium in radioactive rock layers and comparing it to the amount of lead they contain, thus deducing the rock's formation age. Today, scientists believe that the Earth formed between 2 billion and 5 billion years ago. Radioactivity is also used to determine the age of animal and plant remains. All living organisms contain the radioactive element carbon-14, which decays at a certain rate. By measuring the amount of decay, scientists can determine the age of plants and animals. P7-P10