1900: As the twentieth century dawns, scientists have few hard facts about the origins of Earth, humans, or life itself. Most believe the Earth was formed from material torn from the sun, and that as it cooled, its surface contracted, buckled, and cracked, creating mountains and oceans and causing earthquakes and volcanoes. We know little about our prehistoric ancestors. Our best clues are in the few ancient fossils recovered in Europe and Asia. The mechanism of evolution, by which physical traits are passed from one generation to the next, is unknown.

Here are a few steps on the science odyssey from then to now, including links to activities and databank entries on this site.

• In 1907, scientists find a way to use radioactive decay to determine the age of the Earth, establishing that it is much older than many believed.
  

  Discoveries: Radiometric dating finds Earth is 2.2 billion years old
  

• In 1912, a new theory is set forth, proposing that continents have moved over the ages and were once joined together in one supercontinent. The theory is largely ignored until later in the century.
  

  You Try It: Mountain Maker, Earth Shaker
  Discoveries: Wegener proposes idea of continental drift
  People: Alfred Wegener
  

• In 1913, Arthur Holmes proposes a geologic time scale that pushes the age of the Earth back to 4 billion years.
  

  People: Arthur Holmes
  

• In 1947, further refinements in radiometric dating allow scienctists to pinpoint the age of more recent events.
  

  Discoveries: Libby introduces radiocarbon dating
  

In 1953, a number of discoveries advance our understandings of our origins:
• The hoax of the Piltdown Man is revealed, and new sense can be made about the evolution of the human species;
  

  You Try It: Human Evolution
  Discoveries: Piltdown Man is revealed as fake
  

• A major secret of heredity and of how our bodies function is unlocked;
  

  You Try It: DNA Workshop
  Discoveries: Watson and Crick describe structure of DNA
  People: Francis Crick
  People: Rosalind Franklin
  

• The process that might have led to the establishment of the first life forms on Earth is demonstrated experimentally;
  

  Discoveries: Amino acids are created in laboratory
  

• New evidence supporting continental drift is found by mapping the sea floor.
  

  You Try It: Mountain Maker, Earth Shaker
  Discoveries: Great Global Rift is discovered
  

• Beginning in 1959, several important fossil finds in Africa add to our understanding of human evolution.
  

  You Try It: Human Evolution
  Discoveries: Leakey family discovers human ancestors
  People: The Leakey family
  

• By 1962, the mechanisms that power the movement of continents have been proposed.
  

  You Try It: Mountain Maker, Earth Shaker
  Discoveries: Hess proposes sea-floor spreading
  People: Harry Hess
  

• The following year, further evidence is found to support the theory of sea-floor spreading.
  

  You Try It: Mountain Maker, Earth Shaker
  Discoveries: Magnetic bands provide evidence of sea-floor spreading
  

• During the late 1960s and 1970s, physicist Steven Hawking develops new theories about the origins of the universe, helping to develop theories that explain all forms of matter.
  

  People: Steven Hawking
  

• In 1974, fossils of the earliest hominid to walk upright on two feet are found.
  

  You Try It: Human Evolution
  Discoveries: Johanson finds 3.2 million-year-old Lucy
  

• In 1977, scientists studying the Great Global Rift find life forms that may have resembled the first life on Earth.
  

  Discoveries: Life is found near deep ocean vents
  

• In 1980, evidence for a cosmic catastrophe is used to explain mass extinctions in our Earth's past.
  

  Discoveries: Alvarez finds evidence of dinosaur-killing asteroid
  People: Luis Alvarez
  

• In 1994, fossilized remains of the oldest human ancestor to date are found -- perhaps the common link between us and the chimpanzees.
  

  You Try It: Human Evolution
  Discoveries: 4.4 million-year-old ancestor is found
  

• In 1996, a meteorite of Martian origin found twelve years earlier in Antarctica raises the possibility of life of other planets.
  

  Discoveries: Meteorite from Mars points to possibility of life on other planets
  

Today: Our planet is not a static platform for life. The Earth is dynamic and unpredictable. Its surface is composed of large moving plates that consist of both the continents and oceanic crust. The movement is only a few centimeters a year, but it's enough to reshape the Earth, build mountains, spawn earthquakes, and create volcanoes. The accumulation of fossil finds has shown that the birthplace of the human species is in Africa. With the discovery of the structure of DNA has come an understanding of the mechanism by which chemical molecules pass on the code of heredity, creating the basis for evolution and the diversity of life.