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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.
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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
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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.
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