Chapter 17: The History of Life

Chapter 17: The History of Life

paleontologist
a scientist who studies fossils
fossil record
all the fossils and evidence collected that confirms about the history of life on Earth, and also shows how different groups of organisms, including species, have changed over time
extinct
a species that has died out
relative dating
when the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock
index fossil
a fossil of a species that is easily recognized and that existed for a short period but have had a wide geographic range; used to compare relative ages of fossils
half-life
the length of time required for half of the radioactive atoms in a sample to decay
radioactive dating
the use of half-lives to determine the age of a sample; scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains
geologic time scale
a scale used to represent evolutionary time divided into eras and periods
eras
what the time is divided into between the Precambrian Time and the present; there are 3
Precambrian Time
from 4.6 billion to 544 million years ago; during this time life developed as bacteria and softbodied, multicelled organisms; all rocks formed; first mass extinction probably occurred near the end
Paleozoic Era
544 million to 245 million years ago; early vertebrates and invertebrates
Mesozoic Era
245 million years ago to 65 million years ago; “Age of the Dinosaurs”; mammals began to evolve
Cenozoic Era
65 million years ago to the present; “Age of the Mammals”
periods
subdivisions of eras, ranging in length from tens of millions of years to less than two million years
proteinoid microsphere
a tiny bubble formed by large organic molecules; characteristics of cells: selectively permeable membrane, simple means of storing and releasing energy; origin of cells?
microfossil
a microscopic fossil
endosymbiotic theory
the theory that proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms; organelles used to be their own organisms
mass extinction
an event in which many types of living things die out at the same time
macroevolution
large-scale evolutionary patterns and processes that occur over long periods of time
adaptive radiation
the process in which a single species or small group of species evolves, through natural selection and other processes, into diverse forms that live in different ways
convergent evolution
the process by which unrelated organisms come to resemble one another
coevolution
the process by which two species evolve in response to changes in each other over time
punctuated equilibrium
the pattern of long, stable periods interrupted by brief periods of more rapid change