The available astronomical data indicate that the universe is about 13.7 billion years old. This estimate is based, in part, on the observation that the universe is constantly expanding. Astronomers have plotted the trajectories of various stars and galaxies and determined that all matter in the known universe arose from a common point. In an event often referred to as the "Big Bang," the universe arose in a relatively brief moment in time and matter was flung outward from this central origin. Since this beginning, this vast amount of matter has been hurling through space, undergoing changes as it traverses the cosmos. By using radiometric dating techniques (discussed later in this tutorial) of pristine meteorites, astronomers have determined that our own solar system formed 4.55 - 4.56 billion years ago. The Hubble telescope was dispatched in 1990 to explore the far reaches of our galaxy and to photograph astronomical events such as star formation. Astronomers use images captured by the Hubble telescope to further our understanding of the origin of the universe and solar systems.
The Conditions on Early Earth
The earth began to form at the same time as the solar system – about 4.5 billion years ago. The atmosphere on early Earth was strikingly different from that of today. Primitive Earth's atmosphere consisted of methane, ammonia, hydrogen, water vapor, and little free oxygen. This is important because if there was a lot of free oxygen available, life probably could not have arisen from inorganic compounds. This is because oxygen tends to oxidize substances, which means that electrons are removed and substances breakdown (think about the rust forming on a car – eventually oxidation will make the car nonfunctional). Instead, the early earth’s atmosphere was highly reducing which made inorganic molecules capable of gaining electrons and forming more complex molecules. A reducing environment would have been conducive to the evolution of the first bacteria. Because there was little oxygen in the environment – these first life forms would have been anaerobic (or non-oxygen using). Eventually, cyanobacteria evolved photosynthesis - a process that releases oxygen. This important event began the change to what is today’s oxidizing atmosphere. We can learn about these changes from a world full of anaerobic prokaryotes to the world full of the biodiversity we see today by studying the fossil record and other types of evidence. In this class, we will focus on learning about the fossil record.