What is life? Why is there life on Earth, but not on any other planets in the solar system (as far as we know…). Life on Earth occurs in a bewildering array of forms – plants, animals, fungi, protists, and bacteria, which together compose Earth’s biosphere. The biosphere is connected to the Earth System through biogeochemical cycles. Explore the links in this section to learn more about the stuff life is made of, genetics, the diversity of living things, how they coexist in ecosystems and evolve over time, and how life survives in extreme environments.
The <a href="/earth/Life/shark.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">living things that survive in the open ocean</a> need to have a way to float or swim in ocean water.  In the open ocean there are many types of swimmers including fish, <a href="/earth/Life/whale.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">whales</a>, and <a href="/earth/Life/shark.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">sharks</a>. Some fish, such as herring and tuna, swim in schools while others swim alone. Whales strain <a href="/earth/Life/plankton.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">plankton</a> from the sea or they eat fish.<p><small><em> Courtesy of  NOAA</em></small></p><a href="/earth/Life/autotrophs.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">Autotrophs</a> are organisms that can "make their own food" from an inorganic source of carbon (carbon dioxide) given a source of energy. Most autotrophs use sunlight in the process of <a href="/earth/Life/photosynthesis.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">photosynthesis</a> to make their own food. Alga (singular of algae) is an an autotroph because it is capable of photosynthesis.<p><small><em> Image courtesy of Corel Photography</em></small></p>Why did the dinosaurs go <a href="/earth/past/KTextinction.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">extinct</a>? No one knows for sure, and scientists have come up with a number of theories to explain why the dinosaurs suddenly died out about <a href="/earth/past/geologic_time.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">65 million years ago</a>. It wasn't just the dinosaurs that went extinct--roughly two thirds of all of the plant and animal species on Earth disappeared, too!<p><small><em>Image courtesy of the National Science Foundation.</em></small></p><a href="/earth/Life/plankton.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">Plankton</a> are a diverse set of <a href="/earth/Life/ocean_life.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">marine organisms</a>. They can live in salt and fresh water. Although some forms are able to move independently, most plankton drift with the <a href="/earth/Water/ocean_currents.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">water currents</a>. This photo shows an amphipod, a type of plankton, at high magnification.<p><small><em>Image courtesy of Uwe Kils.  Creative Commons Attribution ShareAlike 3.0 License.</em></small></p><a href="/earth/Life/photosynthesis.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">Photosynthesis</a> is the name of the process by which <a href="/earth/Life/autotrophs.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">autotrophs</a> (self-feeders) convert <a href="/earth/Water/overview.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">water</a>, <a href="/physical_science/chemistry/carbon_dioxide.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">carbon dioxide</a>, and <a href="/sun/effect_on_earth.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">solar energy</a> into sugars and <a href="/physical_science/chemistry/oxygen_molecular.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">oxygen</a>. It is a complex chemical process by which <a href="/earth/Life/plantae.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">plants</a> and other autotrophs create the energy needed for life.<p><small><em>Image has been released into public domain (found on <a href=""></a>).</em></small></p>Hydrothermal vents in the deep ocean are located at tectonic <a
  ridges</a>. While most of the water in the deep ocean is close to freezing,
  the water at hydrothermal vents is very hot and laden with chemicals. In
  this <a
  environment</a>, certain species of <a
  and <a
  thrive, enabling a unique <a
  chain</a> including fish, shrimp, giant tubeworms, mussels, crabs, and clams.<p><small><em> Courtesy of NASA</em></small></p>

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA