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Chapter 26 The Tree of Life: - page 4 / 18





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Researchers are looking outside of Earth for clues about the origin of life.

Evidence is growing that Mars was relatively warm for a brief period, with liquid water and an atmosphere rich in carbon dioxide.

During that period, prebiotic chemistry similar to that on early Earth may have occurred on Mars.

Did life evolve on Mars and then die out, or did dropping temperatures and a thinning atmosphere terminate prebiotic chemistry before life evolved?

Liquid water lies beneath the ice-covered surface of Europa, one of Jupiter’s moons, raising the possibility that Europa’s hidden ocean may harbor life.

Detection of free oxygen in the atmosphere of any planets outside our solar system would be strongly suggestive of oxygenic photosynthesis.

Laboratory simulations of early-Earth conditions have produced organic polymers.

The abiotic origin hypothesis predicts that monomers should link to form polymers without enzymes and other cellular equipment.

Researchers have produced polymers, including polypeptides, after dripping solutions of monomers onto hot sand, clay, or rock.

Similar conditions likely existed on early Earth at deep-sea vents or when dilute solutions of monomers splashed onto fresh lava.

Protobionts can form by self-assembly.

Life is defined by two properties: accurate replication and metabolism.

Neither property can exist without the other.

DNA molecules carry genetic information, including the information needed for accurate replication.

The replication of DNA requires elaborate enzymatic machinery, along with a copious supply of nucleotide building blocks provided by cell metabolism.

Although Miller-Urey experiments have yielded some of the nitrogenous bases of DNA and RNA, they have not produced anything like nucleotides.

Thus, nucleotides were likely not part of the early organic soup.

Self-replicating molecules and a metabolism-like source of the building blocks must have appeared together.

Lecture Outline for Campbell/Reece Biology, 7th Edition, © Pearson Education, Inc. 26-4

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