Science Beyond, the role of tectonic processes on climate and environmental
systems is reviewed, while in Climate History
Beyond the development of Homo sapiens and other biologic life
forms is briefly summarized. Resources Beyond
provides an overview of the Snowball Earth theory as well as links to sites
that relate to the evolution of the universe in general and Earth in particular.
Million Years Dominated by
the Pleistocene Ice Ages, the past million years have seen the migration
of hominids, mastering the use
of fire and tracking now-extinct animals such as Mastodon and Woolly
The entire Pleistocene Epoch, from 1.8 Ma (Million Years Ago) to
10,000 years ago is characterized by climatic oscillations and cycles
of glaciation and melting.
Million Years Over the past
10 million years, hominids evolved in and around the Mediterranean
Basin, which was cut off from the Atlantic Ocean. Around seven million
years ago, the basin dried out and reflooded several times, leaving
salt deposits of up to 6,500 feet. These deposits, formed during
an event known as the Messinian Salinity Crisis, created changes
in ocean circulation felt around the world.
Hominids, including Ramapithecus
(10-4 Ma) and Australopithecus (4-1 Ma) such as the famous
Lucy, evolved during this period.
Million Years The dinosaurs
shown here lived during the Late Cretaceous Period (70 million years
ago) after the dinosaurs had achieved their greatest variety, only
five million years before dinosaurs became extinct. The largest
abrupt event of the last 100 Ma occurred when a meteor hit the region
of Yucatan causing mass extinction about 65 million years ago, triggering
the extinction of the dinosaurs and beginning the reign of mammals.
This shift is known as the Cretaceous-Tertiary (KT) boundary.
The transient Paleocene-Eocene
Thermal Maximum at 55 mya and the more robust Early Eocene climatic
optimum around 52 mya were caused by elevated greenhouse gas levels.
The warming of the planet such anomalies as palm trees in Alaska
and crocodiles in the Arctic. Mammals, including the lemurs which
are early ancestors of primates thrive, migrating to Europe and
the Americas from Asia around this time (Beard,
Around 34 million years
ago, the Antarctic ice sheet began to form, and some 20 million
years back, major modern mountain ranges such as the the Cordilleras,
the Andes, and the Himalayan range were formed, with mammals becoming
During the past billion
years, the Earth has undergone major continental shifts, such as
the formation a billion years ago of the supercontinent Rodinia
and its subsequent breakup 750 million years ago .
It has also undergone protracted intervals of severe glaciation,
including the Sturtian glaciation 770-720 million years ago and
the Varanger/Marinoan glaciation 610-575 million years ago when
continental ice sheets existed at low latitudes.
Archaea and cyanobacteria
dating back to over 2.5 billion years ago eventually led to the
development of more complex organisms. Fossils of the earliest known
soft-bodied metazoans (early Ediacaran fauna) date back to about
590 million years ago, and during the Cambrian period an explosion
of biologic life led to the appearance of many diverse marine invertebrates
with exoskeletons. Early fish arrived around 410 million years ago.
The largest mass extinction
in Earth's history possibly caused by an asteroid's impact with
Earth occurred around 250 million years ago that particularly affected
Earth has made an estimated
4.55 billion revolutions around the sun. Using the Earth's annual
unit of time, scientists estimate the universe is another 10 billion
years older than Earth.
Some seven billion years
ago, galaxies and star systems began to evolve, with White Dwarf
stars serving as pressure cookers to create most of the rest of
the elements that we find in the atomic chart.
Once Earth and the rest
of our solar system were formed, liquid water quickly developed
with the planet's climate stabilizing to prevent all the water from
completely freezing or evaporating-- creating an environment from
which biologic life began to develop. Although less intense than
today, solar radiation bombarded Earth which initially didn't have
protective atmosphere to shield early life forms from this radiation.
Photosynthesis provided the means to transform solar energy, water
and atmospheric carbon dioxide into fuel that could be stored for
later use, and in the process they changed the composition of the
atmosphere by removing carbon dioxide and replacing it with free
oxygen (O2). By two billion years ago, atmospheric oxygen
and likely ozone had already reached substantial levels. As researchers
such as Lynn Margulis
shown, biological organisms such as microbes have long influenced
climate on Earth.
Beginning to Time
our primary measures of time-- years and days-- did not exist prior
to Earth's birth some 4.55 billion orbits of the sun ago, we use
the measure of a year to extrapolate to the time before Earth existed.
According to many cosmologists, the scientists who study the origins
of the universe, a "Big Bang" event that spontaneously
created the universe occurred some 14 or 15 billion years ago. The
only "thing" that existed as matter was the element hydrogen,
which over hundreds of millions of years began to break down into
helium and generate photons which release light.