The Habitable PlanetHabitable Planet home page

Unit 1: Many Planets, One Earth // Visuals

Animation(s)

Carbon dioxide in the atmosphere
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
Clues to oxygen formation
Banded iron formations around the world offer important clues to oxygen formation. View animation

Fossil timeline
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
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
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
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
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)
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
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 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, 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
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
Cenozoic cooling
Sharp cooling during the Cenozoic era promoted the rise of mammals. View image

Comparison of Venus and Earth
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
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.
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
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
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
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
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
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
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
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
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
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
The universal Tree of Life
As the Tree of Life shows, microbes were the dominant early life forms on Earth. View image

top of page

© Annenberg Foundation 2014. All rights reserved. Legal Policy