The origin of life is one of the great mysteries in the Universe. To determine the origin of life, scientists are investigating the problem in several different ways. Some scientists are studying life on our own planet. Some scientists are seeking out life or fossil life on other planets or moons in our solar system. And other scientists are trying to detect life in other solar systems, either by measuring life's effects on the atmospheres of distant planets or by measuring artificial radiation like radio signals that may be produced by advanced life.
the most fruitful approach has been to examine life on our own planet.
However, even in our own backyard, it is difficult to determine life's
origins because it began at least 3.5 billion years ago. We know
that life began at least 3.5 billion years ago, because that is the age
of the oldest rocks with fossil evidence of life on earth. These
rocks are rare because subsequent geologic processes have reshaped the
surface of our planet, often destroying older rocks while making new ones.
Nonetheless, 3.5 billion year old rocks with fossils can be found in Africa
and Australia. They are usually a mix of solidified volcanic lavas
and sedimentary cherts. The fossils occur in sedimentary cherts.
Above) 3.5 billion year old lava. Above Right) 3.5 billion year old sedimentary chert.
Chemical traces of life have also been detected in slightly older rocks. In Greenland, a series of ancient metamorphosed sediments have been found. Analyses indicate the sediments were deposited about 3.8 billion years ago. They also revealed carbon isotope signatures that appear to have been produced by organisms that lived when the sediments were deposited.
In all cases, life as we understand it must have water. This general rule is true on Earth and is thought to be true elsewhere in the solar system. Currently, life is being sought on Mars where water may have once flowed on the surface and Europa where a subterranean sea of water may exist beneath its icy surface.
If one analyzes
the genetic information in a variety of modern organisms living on Earth,
one can begin to group and separate organisms based on their common (or
disparate) properties. This type of analyses is intuitive at some
levels. For example, most people recognize that mule deer and white
tail deer are more closely related than mule deer and grizzly bears.
Consequently, in a tree of life, mule deer would appear closer to white
tail deer than grizzly bears. This same process can be applied to
all organisms and has led to three large domains of life: Bacteria, Archaea,
and Eukarya. Humans, as well as other complex mammals, are part of
the Eukarya group. If one traces the genetic information in organisms
in all three groups, it appears they have a common ancestor or at least
ancestors that share a common set of traits. In either case, it appears
the earlist form of life in the tree of life were thermophilic or hyperthermophilic
organism, which means they lived in systems composed of hot water.
Above) Examples of modern thermophilic organisms.
systems are called hydrothermal systems. These can be found in areas
of volcanic activity where hot molten rock beneath the surface heats groundwater.
Hydrothermal systems produce hot springs and geysers at the surface.
Good examples include Yellowstone on the United States and Rotorua in New
Above) Yellowstone hot springs
Recently, Kring and his colleagues have been investigating impact-generated hydrothermal systems. The energy deposited by an impact event is so great that it can easily heat water and cause it to circulate through the Earth's crust. Examples of impact-generated systems have been found at several impact craters around the world. And although none of them are active today, they likely produced hot springs and geysers similar to those produced by magmatic activity beneath the surface of the Earth.
Early in Earth's history, both volcanism and impact cratering were very common processes. So both may have provided the environments needed to transform disparate chemical compounds into living organisms and may have provided a suitable habitat for that life to evolve.
Was the origin of life connected to the lunar cataclysm?
This web site is based on information originally created for the NASA/UA Space Imagery Centerís Impact Cratering Series.
Concept and content by David A. Kring.
Design, graphics, and images by Jake Bailey and David A. Kring.
Any use of the information and images requires permission of the Space Imagery Center and/or David A. Kring (now at LPI).