*METABOLISM *
- First
Some scientists believe that metabolism, in other words - the ability to break down carbon dioxide in the presence of a catalyst into small organic molecules - was how the first life developed. These reactions might have evolved to become more complex, and then genetic molecules somehow formed and joined in later. There are many different theories as to exactly what types of molecules and catalysts would have been involved.
* GENES *
- First
Other scientists believe that the first living organisms were genes. These genes were single molecules that had developed in such a way as to be able to catalyze their own replication. This theory seems more likely, since even simple systems such as crystals, have been demonstrated to evolve with modifications that breed true. Some scientists have suggested that certain compositions of clay create the right environment for these reactions to propagate.
*RNA*
is a complex molecule found in all living things that seems to be able to catalyze its own reproduction. Many scientists believe that simple RNA molecules developed and eventually became more complex and developed into the organisms we see today.
* LUCA*
Astrobiologists and biochemists want to understand something they call LUCA (the Last Universal Common Ancestor). The idea is that all life on Earth has a common ancestor, kind of like a great-great-great-....-great grandmother. They search for traits that are common across all life forms and assume that any traits that are common to all life forms today must have been inherited from LUCA, who had them all as well.
Biochemists know quite a bit about LUCA and her biochemistry. She stored her genetic information in DNA, she had several hundred proteins performing a variety of functions, and she used the same 20 amino acids we use in our proteins. She used RNA and had some kind of double-layer lipid membrane. She was probably the ancestor of the three kingdoms of life: Archaea, Eukaryotes and Bacteria.
LUCA lived at least 2 billion years ago, before there was much oxygen in the atmosphere. She used enzymes containing iron in her metabolic pathways the way much life on early Earth did. Studying how life arose on Earth is useful to astrobiologists, but they keep in mind that the way life formed on Earth is not the only way life could have formed. It is simply one way that it did.
- First
Some scientists believe that metabolism, in other words - the ability to break down carbon dioxide in the presence of a catalyst into small organic molecules - was how the first life developed. These reactions might have evolved to become more complex, and then genetic molecules somehow formed and joined in later. There are many different theories as to exactly what types of molecules and catalysts would have been involved.
* GENES *
- First
Other scientists believe that the first living organisms were genes. These genes were single molecules that had developed in such a way as to be able to catalyze their own replication. This theory seems more likely, since even simple systems such as crystals, have been demonstrated to evolve with modifications that breed true. Some scientists have suggested that certain compositions of clay create the right environment for these reactions to propagate.
*RNA*
is a complex molecule found in all living things that seems to be able to catalyze its own reproduction. Many scientists believe that simple RNA molecules developed and eventually became more complex and developed into the organisms we see today.
* LUCA*
Astrobiologists and biochemists want to understand something they call LUCA (the Last Universal Common Ancestor). The idea is that all life on Earth has a common ancestor, kind of like a great-great-great-....-great grandmother. They search for traits that are common across all life forms and assume that any traits that are common to all life forms today must have been inherited from LUCA, who had them all as well.
Biochemists know quite a bit about LUCA and her biochemistry. She stored her genetic information in DNA, she had several hundred proteins performing a variety of functions, and she used the same 20 amino acids we use in our proteins. She used RNA and had some kind of double-layer lipid membrane. She was probably the ancestor of the three kingdoms of life: Archaea, Eukaryotes and Bacteria.
LUCA lived at least 2 billion years ago, before there was much oxygen in the atmosphere. She used enzymes containing iron in her metabolic pathways the way much life on early Earth did. Studying how life arose on Earth is useful to astrobiologists, but they keep in mind that the way life formed on Earth is not the only way life could have formed. It is simply one way that it did.
