33.4: What is Evolutionary History?
Scientists record evolutionary history by analyzing fossil, morphological, and genetic data. The fossil record documents the history of life on Earth and provides evidence for evolution. However, both fossil and living organisms offer evidence that outlines Earth’s evolutionary history.
Phylogenetic trees illustrate the evolutionary relationships among these organisms. Scientists infer organisms’ common ancestry by evaluating shared morphological and genetic characteristics. Together, the fossil record and phylogenetic trees help scientists to reconstruct the evolutionary history of life on Earth.
According to evolutionary history, conditions on early Earth set the stage for life to begin. Nearly 4 billion years ago, atmospheric water vapor condensed into rain that filled the planet’s basins to form oceans. Consequently, as documented by fossil evidence, life on Earth began with the advent of unicellular life.
Scientists, such as astrobiologists, use this knowledge to research the potential for life on other planets. The presence of water is presumed to be a universally shared requirement for life. Water found on Mars, for example, suggests that life—most likely bacteria—may exist on that planet as well.
As conditions changed on Earth, organisms’ complexity and variety also changed. Oxygenation of Earth’s atmosphere paved the way for multicellular life and land colonization. Over time, countless species emerged (i.e., speciation) and perished (i.e., extinction) as Earth endured environmental shifts.
Throughout evolutionary time, species developed adaptations to better survive the Earth’s dynamic environment. Adaptations can arise from either a common ancestor or independently via convergent evolution. For example, a common ancestor gave rise to the shared forelimb structure of mammals, while the fins and tails of fish evolved independently from that of whales.
Evolutionary history describes how fossil and living species evolved since life’s emergence on Earth. Scientists aim to understand the environmental forces driving evolution as well as evolutionary relationships between organisms. Establishing Earth’s evolutionary history provides a framework for understanding the process and circumstances surrounding evolution.