How Life Began Origins Nova Neil Degrasse Tyson HD

Summary

The program examines how life may have arisen on a young Earth and how microbes transformed the planet. It emphasizes that the precise pathway from nonliving chemistry to life remains unknown.

Early Earth

About 4.5 billion years ago, Earth was extremely hot and geologically violent. Its atmosphere and oceans differed greatly from today’s, and impacts from asteroids and comets repeatedly heated or vaporized the surface. The program describes the first 600 million years as a period of heavy bombardment.

The chemical ingredients of life

Living things rely on elements including carbon, hydrogen, oxygen, and nitrogen. Carbon is especially useful for building complex molecules because it can form many kinds of bonds.

In the 1950s, Stanley Miller used flasks, water, gases thought at the time to represent the early atmosphere, and electrical sparks simulating lightning. The experiment produced amino acids, important components of proteins. Scientists still debate whether Miller’s atmospheric mixture accurately represented early Earth.

Space dust and meteorites can contain organic compounds, including amino acids, and may have delivered some ingredients for life to early Earth. Experiments firing amino-acid solutions at high speed found that impact conditions could leave material intact and, in some cases, promote the formation of larger molecules called peptides.

Evidence for ancient life

Researchers examined rocks from Greenland estimated to be 3.7–3.9 billion years old. Because fossils in such rocks may have been destroyed, they looked for chemical traces of biological activity. The proposed evidence is controversial.

Studies of Villa Luz Cave in Mexico and deep South African mines show that microbes can live in conditions hostile to humans. Cave bacteria use hydrogen sulfide for chemical energy, while deep-underground microbes may use gases such as methane, ethane, and propane. These ecosystems offer clues to environments where early life might have survived.

The program considers whether life could have persisted underground or around seafloor volcanic vents during the era of impacts. Modern vent ecosystems support microbes that obtain energy from chemicals rather than sunlight.

Photosynthesis and oxygen

After impacts became less frequent, some microbes developed photosynthesis, using sunlight to make food from carbon dioxide and water. Stromatolites—layered structures built by microbial communities—provide evidence of ancient microbial life. Modern stromatolites are built in part by photosynthetic cyanobacteria.

Oxygen produced by cyanobacteria first reacted with iron in the oceans, contributing to iron-ore deposits. Later, oxygen accumulated in the atmosphere, eventually reaching roughly today’s level of 21%. It also helped form the ozone layer, which reduced harmful ultraviolet radiation.

Microbes and evolution

Microbes dominated Earth for most of its history. Their production of oxygen helped create conditions in which complex organisms could evolve. The program’s compressed “24-hour” timeline illustrates how late visible multicellular life—and especially humans—appeared in Earth’s history.

Researchers and featured sources

Researchers and host

• Neil deGrasse Tyson — host
• Penny Boston — microbiologist
• Diana Northup — microbiologist
• Stanley Miller — chemist known for the early-Earth chemistry experiment discussed
• Mojzsis — researcher studying ancient Greenland rocks; the subtitles give only his surname
• Don Brownlee — researcher studying extraterrestrial dust
• Jennifer Blank — researcher conducting impact experiments
• Martin Van Kranendonk — geologist studying ancient stromatolites

Program and credited organizations

• NOVA / WGBH Boston
• National Science Foundation
• NASA Office of Space Sciences
• Alfred P. Sloan Foundation
• George D. Smith Fund
• Park Foundation
• Sprint
• Microsoft
• Corporation for Public Broadcasting
• PBS viewers