BIOL 102 Chapter 1: Deep History of Life on Earth Simulation
Document Summary
Earth is over 4 billion years old. Scientists think there has been life on earth for at least 3. 5 billion years. For the most part, microbial life was the only life present (still dominate many ecosystems today) Dramatic increase in oceanic and atmospheric oxygen made it possible for multicellular life to develop. Scientists have constructed the timeline of life on earth from 2 main types of evidence. Most familiar type = fossils provide detailed glimpses of ancient life for larger, more recent organisms. Molecular traces, cholesterol + other chemical signatures, isotope ratios resulting from living processes, banded iron formations (markers of environmental conditions), features in limestone reflecting microbial interactions w/ sediments. Earth formed from the growth/accumulation of interstellar dust + debris. The growing mass (proto-earth) was compressed by gravity causing an increase in temperature. + additional heat from radioactive decay caused proto-earth to become a hot molten mass. As proto-earth cooled, it stratified according to density causing a layered composition.
