Unit 1: Many Planets, One Earth // Visuals

Animation(s)

Carbon dioxide in the atmosphere: Carbon dioxide is a "greenhouse gas" that helps to regulate the Earth's temperature. An increase in levels of atmospheric carbon dioxide results in higher global temperatures. View animation
Clues to oxygen formation: Banded iron formations around the world offer important clues to oxygen formation. View animation
Fossil timeline: The fossil record provides direct evidence that Earth's first animals emerged approximately 600 million years ago. View animation
Scientific evidence for a "Snowball Earth": The "Snowball Earth" hypothesis proposes that the Earth was entirely covered by ice for long periods, hundreds of millions of years ago. View animation
The rise of oxygen: Oxygen became abundant on Earth when complex animal life started to appear. View animation

Photograph(s)

Banded iron formation from Ontario, Canada: As early photosynthesis began to raise atmospheric oxygen levels about 2.7 billion years ago, iron precipitated out of seawater, creating banded iron formations like this specimen from Ontario, Canada. View image
Evidence of glaciation in seaside rocks, Massachusetts: Geologist Paul Hoffman points out glacial dropstones, small rounded pebbles imbedded in otherwise neat layers of sedimentary rock 500-600 million years old. View image
Fossils of Kimberella (thought to be a jellyfish): Kimberella was originally thought to be a type of jellyfish, but scientists now believe that it had rigid parts (probably a hard, shell-like covering) which formed the deep depressions in these fossils. View image
Model of Archaeopteryx fossil: Archaeopteryx had some features not seen in today's birds, such as a long bony tail and a full set of teeth. However, it also had feathers, wings, and reduced fingers, which are characteristic of modern birds. View image
Stromatolites at Hamelin Pool, Shark Bay, Australia: Stromatolites are uncommon today because burrowing and grazing organisms destabilize marine sediments and consume the microbial mats produced by cyanobacteria. Exceptions occur in hyper-saline environments, like Shark Bay, where few organisms can survive. View image
The Willamette Meteorite, the largest ever found in the United States (15 tons): The Willamette Meteorite is probably a fragment from the core of an ancient planet that broke up as it orbited the sun. Its structure suggests that it sustained at least two high-energy impacts in space before it fell to Earth's surface and weathered further. View image

Graphic(s)

Atmospheric oxygen levels over geological time: Increases in atmospheric oxygen levels are closely correlated with hypothesized Snowball Earth episodes and with the appearance of increasingly complex life forms. View image
Cenozoic cooling: Sharp cooling during the Cenozoic era promoted the rise of mammals. View image
Comparison of Venus and Earth: Venus and Earth are roughly the same size, but Venus has a much thicker atmosphere and its surface conditions are inhospitable to life. View image
Cycling of carbon and oxygen: Photosynthesis removes CO₂ from the air and adds oxygen, while cellular respiration removes oxygen from the air and adds CO₂. The processes generally balance each other out. View image
Geologic history of southern California.: Scientists study characteristics of a geologic stratum such as color and mineral type so that they can match up portions of that stratum that are exposed in separate regions. Strata can extend for many miles, although they may only be exposed in a few places. View image
Gondwanaland: Gondwanaland started to fragment and drift apart during the Mesozoic era, eventually creating the modern continents. This process changed ocean circulation patterns and altered Earth's climate. View image
Marine genus biodiversity: This graph shows the fraction of marine genera that were present in an interval of time but did not exist in the following interval. It includes a selection of marine organisms that were easily preserved as fossils, not the entire inventory of living species. View image
Oxidation of iron to form rust: In oxidation reactions such as rust formation, a molecule or atom loses electrons and becomes more positively charged. Although it can also take place with other chemicals, oxidation is so named because the first such reactions to be thoroughly studied were reactions with oxygen. View image
Sample geologic cross-section: Geologic cross-sections are vertical slices through rock formations. Earth scientists analyze cross-sections to map an area's geological history. View image
The breakup of Rodinia: Rodinia was Earth's main land mass from about 1.2 billion to 750 million years ago, surrounded by a single planetary ocean. View image
The faint, young sun and temperatures on Earth: Based on the strength of the young sun, the early Earth should have been frozen over. However, greenhouse gases in Earth's atmosphere retained enough heat to provide liquid water on Earth's surface. View image
The geochemical carbon cycle: A silicate weathering feedback adjusts atmospheric CO₂ sources and sinks. Plate tectonics recycle sedimentary carbon (carbonate and organic matter) as volcanic and metamorphic CO₂. View image
The geochemical carbon cycle on a Snowball Earth: On a Snowball Earth, volcanic and metamorphic CO₂ sources are unaffected, but the absence of rainfall reduces CO₂ removal from the atmosphere. Ice cover and cold ground temperatures reduce silicate weathering. View image
The geologic time scale: The geologic time scale divides Earth's history into blocks of time that are ordered sequentially and read from bottom to top, like the rock records on which it is based. View image
The universal Tree of Life: As the Tree of Life shows, microbes were the dominant early life forms on Earth. View image

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