Origins of Life

Abiogenesis This origin of life from nonliving matter is called abiogenesis, sometimes referred to as spontaneous generation. Scientists have found that marine life fossils are significantly older than fossils of terrestrial life. The oldest fossils are those of cyanabacteria, dated 3.5 billion years ago. Cyanobacteria are aquatic, photosynthetic bacteria (blue-green algae). The oldest terrestrial fossils found are about one billion years old.

It’s not exactly clear how the first molecular building blocks for life came about. In 1929, scientist J.B.S. Haldane proposed that they could have originated from lightening or ultraviolet light in the atmosphere. In 1953 Stanley Miller and Harold Urey tested Haldane’s hypothesis by discharging electricity within the gasses Haldane proposed. The gasses included: water vapor, ammonia, methane, and hydrogen.

The Urey-Miller experiment produced amino acids – the component molecules that living systems use to build protein. This experiment did not produce life. The main point of the Urey-Miller experiment and subsequent discoveries is that many basic molecules used by living systems readily form under certain conditions.

other hypothesis of how life originated First life arose from a “primordial soup”. Life arose deep in the ocean, protected by water. The first organic material or life itself arrived from space via a comet or meteor.

Regardless of the exact environment that allowed it to happen, biologists propose that simple molecules randomly combined and separated. Eventually large, more stable molecules formed by chance. When one of these combinations became capable of reproducing itself, life was born.

Oxygen and Evolution

Heterotroph versus Autotroph The first organisms were very simple. They probably thrived by breaking down simple compounds in the “primordial soup” to supply their energy. Organisms that rely on consuming compounds to obtain chemical energy are called heterotrophs. As life became more advanced, about 3 to 3.5 billion years ago, the first autotrophs appeared. Autotrophs can create organic energy compounds from inorganic compounds and an external energy source. Autotrophs began breaking down carbon dioxide into oxygen. This raised the atmosphere’s oxygen content from 1% to the present 21%.

Why use Oxygen? Oxygen is important to life because oxygen reactions allow organisms to use chemical energy more effectively. Biologists theorize that the availability of oxygen allowed the development of mitochondria – structures within cells that process oxygen as they use energy. Mitochondria make oxygen use more effective, and are found in more complex organisms.

The theory of evolution was originally proposed by Charles Darwin in his 1859 book On the Origin of Species by Means of Natural Selection. The theory of evolution is based on the principle that in nature, various characteristics affect survival.

Organisms produce more offspring than can survive to adulthood, so those with favorable characteristics are more likely than those with less favorable characteristics to survive and reproduce. This is called natural selection. Sometimes new characteristics appear in an organism due to mutation. The theory of evolution says that over long periods (millions of years) natural selection and mutation caused the development of all the different life forms and their characteristics. Organisms became more varied and complex over millions of years. The prevailing view in evolution is that changes come in spurts due to significant changes in the environment. These changes cause some species to become extinct. Existing organisms adapt and become new species as they fill niches left by extinct species.

It is argued that single-celled organisms then evolved from independent existence to life in colonies. Over millions of years, these colonies evolved into complex multicellular organisms. The first multicellular organisms lived in the ocean. Over time, evolutionary processes allowed organisms to adapt to life on land, and terrestrial and marine organisms have continued to evolve. Biologists theorize that it is this process that specifically adapted organisms to the hundreds of environments in which they live.