What is earths history divided into time units that make up a geologic time scale.
geologic time
What is the longest time period, based on fossils?
Eons
What is the second longest time period, marked by worldwide changes in the types of fossils in rock?
Eras
What is the third longest period of time, based on types of life existing worldwide at a particular time
priods
What is a period of time characterized by DIFFERENCES IN LIFE FORMS but differences can be regional rather than global
epochs
Geologic time can be subdivided only if ______________________ are present in ______________________ records.
fossil: rocks
______________________ evolution is how organisms have ______________________ over time, most likely because of ______________________ changes.
organic, changed, environmental
______________________ theory of ______________________ states that organisms more adapted to an environment are more likely to ______________________.
Darwin's, natural selection, reproduce
______________________ selection within a species occurs only if ______________________ present in some numbers increase their ______________________
natural characteristics, survival
______________________ selections is the ______________________ of individuals with ______________________ characteristics; humans use this type of selection when breeding ______________________ animals.
Artificial, breeding, desired, domestic
New species can ______________________ from natural selection.
evolve
______________________ have an exoskeleton with ______________________ lobed and lived in oceans for more than ______________________ million years.
trilobites, 3, 200
Trilobites ______________________ position changed as the species adapted to various environments.
eye
Trilobite bodies and tail changed in response to changing ______________________.
environments
______________________ collisions formed the giant landmass ______________________ near the end of the Paleozoic Era. These collisions may have ______________________ sea levels, causing the ______________________ of trilobites.
continental, Pangaea, dropped, extinction
Precambrian time is The ______________________ part of Earth's history.
longest
______________________ appeared toward the end of this time.
invertebrates
Late in this time a group of animals with shapes similar to modern ______________________, ______________________, and ______________________ lived. Fossils of these organisms were first found in ______________________.
jellyfish, worms, soft coral, australia
Very ______________________ fossils remain from this time.
few
Many Precambrian rocks were ______________________ buried, causing the fossils in them to be ______________________ by heat and pressure.
deeply, changed
Most Precambrian organisms ______________________ hard parts.
lacked
______________________ are classified as blue-green algae.
cyanobacteria
They were one of the ______________________ life forms to appear, appearing about ______________________.
earliest, 3.5 billion years ago
They added ______________________ to the atmosphere through
_____________________. Because of this the ______________________ layer in the atmosphere began to develop, shielding Earth from ______________________ rays. It is thought that these changes allo
oxygen, photosynthesis, ozone, ultra violet, complex
______________________ appeared late in Precambrian time.
invertebrates
An abundance of organisms with ______________________, such as ______________________, marks the beginning of this era.
Hard parts, shells
Most lifeforms of this era lived in the ______________________.
ocean
______________________ also evolved during this time. The first vertebrates were ______________________ creatures with jaws. Some of these fish were so huge that they could eat large sharks with their powerful jaws.
vertebrates, fishlike
During this time, ______________________ appeared and ______________________ began to adapt to land environments.
forest, vertebrates
Paleontologists know that many ancient fish had ______________________ as well as ______________________. Lungs enable these fish to live in water with low oxygen levels- when needed they could swim to the surface and breathe air.
lungs, gills
One kind of ancient fish had lungs and ______________________ fins, which were used to swim and crawl around on the bottom. Scientists hypothesize that ______________________ might have evolved from this kind of fish.
leg like, amphibians
The ______________________ Mountains formed during this time.
appalachian
At the end of this era, about ______________________ of all marine species and ______________________ of all land species died off due to changes in ______________________ and a lowering of ______________________.
85%, 70%, climate, sea level
Mesozoic era Called the era of ______________________ life.
middle
______________________ lived during this time. Scientists have studied the ______________________ to calculate how fast these animals ______________________ or ______________________.
Dinosaurs, fossil footprints, walked, run
Studies also show that dinosaurs might have been ______________________.
warm blooded
Fossil records also indicates that some dinosaurs ______________________ their young and ______________________ in herds.
nurtured, traveled
At the beginning of this time all the continents were joined as ______________________; then the continents ______________________ broke apart and formed the continents we know today.
Pangaea, slowly
______________________ were the most abundant animals on land.
reptiles
______________________ also appeared during this time and scientists think they evolved from ______________________, ______________________ dinosaurs.
Birds, small, meat eating
The earliest birds had ______________________ and ______________________, but it is not a direct ______________________ of today's birds because of other features not shared.
wings, feathers, ancestors
the earliest mammals were small, ______________________ creatures; they were warm-blooded vertebrates that had hair or fur covering their bodies. The females produced milk for their young. These characteristics enabled mammals to survive in many changing
mouse like
______________________ dominated the land. Gymnosperms are plants that produce ______________________ but not ______________________.
Gymnosperms, seeds, flowers
______________________, or flowering plants, evolved at the end of the era and are the most ______________________ and abundant land plants today.
Angiosperms, diverse
ended about 65 million years ago with a major ______________________ of land and ______________________ species. Paleontologist hypothesize that a comet or asteroid ______________________ with earth causing a huge cloud of dust and smoke to rise into the
extinction, marine, collided, blocking
Began about ______________________ years ago and continues today.
65 million
Many ______________________ ranges formed, perhaps creating cooler climates worldwide and creating the ______________________.
mountain, ice ages
______________________ continued to evolve.
mammals
Many species became ______________________ as the continents continued to separate.
isolated
Evidence of this can be seen today in Australia's marsupials. ______________________ are mammals such as kangaroos, koalas, and wombats that carry their young in a pouch.
marsupials
______________________, or humans, appeared about ______________________ years ago.
homo sapiens, 400,000
Some people suggest that the appearance of humans could have led to the ______________________ of many other mammals.
extinction