The History of Life Unit V Chapter 17

Fossils and Ancient Life A fossil is the preserved remains or evidence of an ancient organism Scientists who study fossils are paleontologists The fossil record is the grouping of similar organisms from oldest to most recent It can provide evidence about the history of life on Earth and show how different groups of organisms have changed over time

Extant v/s Extinct More than 99 percent of all species that have ever lived on Earth have become extinct The term extinct is used to describe a species that no longer has a living representative The term extant is used to describe a species that has living representatives

The Formation of Fossils A fossil can be as large and complete as an entire, perfectly preserved animal, or as small as a tiny fragment of a jawbone or leaf For a fossil to form, either the remains of the organism or some trace of its presence must be preserved The formation of any fossil depends on a precise combination of conditions Because of this, the fossil record provides an incomplete record of the history of life – for every organism that leaves a fossil, many more die without leaving a trace

The Formation of Fossils Figure 17-2 Formation of a Fossil The Formation of Fossils Section 17-1 Water carries small rock particles to lakes and seas. Dead organisms are buried by layers of sediment, which forms new rock. The preserved remains may later be discovered and studied. Go to Section:

Radioactive Dating Radioactive dating is the use of half-lives to determine the age of a sample Radioactive elements decay, or break down, into non-radioactive elements at a steady rate called a half-life A half life is the length of time required for half of the radioactive atoms in a sample to decay In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains

Formation of Earth Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water About 4 billion years ago, Earth cooled enough to allow the first solid rocks to form on its surface About 3.8 billion years ago, Earth’s surface cooled enough to allow water to remain liquid Could organic molecules evolve under these conditions?

The First Organic Molecules Section 17-2 Miller and Urey’s experiments suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive earth. Miller and Urey produced amino acids, which are needed to make proteins, by passing sparks through a mixture of hydrogen, methane, ammonia, and water. Spark simulating lightning storms Mixture of gases simulating atmospheres of early Earth Cold water cools chamber, causing droplets to form Condensation chamber Water vapor Liquid containing amino acids and other organic compounds Go to Section:

Origin of Eukaryotic Cells The endosymbiotic theory, championed by Lynn Margulis, proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms Chloroplast Plants and plantlike protists Aerobic bacteria Ancient Prokaryotes Photosynthetic bacteria Nuclear envelope evolving Mitochondrion Primitive Photosynthetic Eukaryote Animals, fungi, and non-plantlike protists Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote Go to Section:

Patterns of Evolution Macroevolution refers to the large scale evolutionary changes that take place over long periods of time Six important patterns of macroevolution are: Mass extinctions Adaptive ratiation Convergent evolution Coevolution Punctuated equilibrium Changes in developmental genes

Mass Extinctions Extinctions occur all the time More than 99% of all species that ever lived are extinct today Usually, extinctions occur at a constant rate Several times, however, huge numbers of species have disappeared in mass extinctions Paleontologists think that most mass extinctions in the past were caused by multiple factors Asteroids Volcanic activity Changing position of continents Changing sea levels

Adaptive Radiation The evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges is called adaptive radiation. Adaptive radiation typically occurs when a few organisms make their way to new, often distant areas or when environmental changes cause numerous extinctions, opening up ecological niches for the survivors. Fossil evidence indicates that mammals underwent a dramatic adaptive radiation after the mass extinctions of dinosaurs 65 mya.

Convergent Evolution Convergent evolution describes 2 unrelated species that share similar traits. These similarities are not due to common ancestry, but rather a result of similar environmental factors.

Coevolution Coevolution describes the evolution of one species in response to new adaptations that appear in another species of which the first shares close interaction

Punctuated Equilibrium Punctuated equilibrium is a pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change Typically occurs when new niches become available following a mass extinction

Developmental Genes & Body Plans Hox Genes are a stretch of DNA sequence found in genes involved in the regulation of the development (morphogenesis) of animals, fungi and plants Correlations between Hox genes and major evolutionary events are apparent…major changes between animal phyla are correlated with duplications in Hox genes or an increase in the number of Hox genes

Speciation Flow Chart Section 17-4 Species Go to Section: that are Unrelated Related form in under under in in Inter-relationshiops Similar environments Intense environmental pressure Small populations Different environments can undergo can undergo can undergo can undergo can undergo Coevolution Convergent evolution Extinction Punctuated equilibrium Adaptive radiation Go to Section: