28.1 Life in the Universe Are we alone?

Cosmic Evolution History of the universe History of the universe Particulate Particulate Galactic Galactic Stellar Stellar Planetary Planetary Chemical Chemical Biological Biological cultural cultural

What is life? Biologists do not agree! Biologists do not agree! General characteristics of life: General characteristics of life: 1. Can react to its environment (often heal themselves when damaged) 2. Can grow by taking in nourishment and process it into energy 3. Can reproduce, passing along characteristics 4. Have the capacity for genetic change and can adapt to a changing environment

Are there exceptions? Stars react to gravity, grow, generate energy and reproduce by triggering the formation of new stars Stars react to gravity, grow, generate energy and reproduce by triggering the formation of new stars A virus is inert until in a living cell – here it seizes control and uses the cell’s genetic makeup to grow and reproduce A virus is inert until in a living cell – here it seizes control and uses the cell’s genetic makeup to grow and reproduce

Assumptions of Mediocrity 1. Because life on Earth depends on just a few basic molecules and 2. Because the elements that makeup these molecules are common to all stars, and 3. If the laws of science we know apply to the entire universe, THEN Life must have originated elsewhere in the cosmos. Life must have originated elsewhere in the cosmos.

Opposing scientific viewpoints Life on Earth is the product of a series of extremely fortunate accidents, unlikely to have occurred anywhere else in the universe Life on Earth is the product of a series of extremely fortunate accidents, unlikely to have occurred anywhere else in the universe

Chemical Evolution Much of what we happened early on (first billion years of so) is not known. Much of what we happened early on (first billion years of so) is not known. It has been erased by geologic activity. It has been erased by geologic activity. We believe that the early earth was barren – no like in the seas or on land. We believe that the early earth was barren – no like in the seas or on land. The atmosphere was rich in hydrogen, nitrogen, and carbon compounds – not much oxygen. The atmosphere was rich in hydrogen, nitrogen, and carbon compounds – not much oxygen. Over time and as Earth cooled, ammonia, methane, carbon dioxide and water formed. Over time and as Earth cooled, ammonia, methane, carbon dioxide and water formed.

Surface of early Earth Violent Violent Radioactivity Radioactivity Lightning Lightning Volcanism Volcanism Solar UV radiation Solar UV radiation Meteorite impacts Meteorite impacts All of these things provide early energy All of these things provide early energy

Formation of Amino Acids and Nucleotide Bases These are organic molecules that are the building blocks of life as we know it. These are organic molecules that are the building blocks of life as we know it. Amino acids build proteins. Amino acids build proteins. Nucleotide bases build genes that contain genetic information. Nucleotide bases build genes that contain genetic information.

Urey-Miller Experiment Based on the idea that complex molecules could have evolved naturally from simpler ingredients found on the primitive Earth. Based on the idea that complex molecules could have evolved naturally from simpler ingredients found on the primitive Earth. Idea has been around since 1920s. Idea has been around since 1920s. Urey and Miller used water, methane, carbon dioxide, and ammonia in an experiment. Urey and Miller used water, methane, carbon dioxide, and ammonia in an experiment. They energized it with an electrical discharge (similar to lightening). They energized it with an electrical discharge (similar to lightening). They produced amino acids. They produced amino acids.

After Urey-Miller The experiment has been reproduced many times, with similar results. The experiment has been reproduced many times, with similar results. Scientists have also been able to synthetically produce nucleotide bases. Scientists have also been able to synthetically produce nucleotide bases. They have not been able to produce DNA. They have not been able to produce DNA.

What their experiment shows… Biological molecules can be made from non- biological molecules. Biological molecules can be made from non- biological molecules. In more advanced experiments, protein-like microspheres have been produced. In more advanced experiments, protein-like microspheres have been produced. While they are not living, they are similar to microspheres found in the fossil record. While they are not living, they are similar to microspheres found in the fossil record.

Interstellar Origin Some scientists believe that the organic material that combined to form the first living cells was produced in interstellar space and subsequently arrived on Earth in the form of comets, interplanetary dust, and meteors. Some scientists believe that the organic material that combined to form the first living cells was produced in interstellar space and subsequently arrived on Earth in the form of comets, interplanetary dust, and meteors. Large amounts of organic material have been detected on comets, such as Halley and Hale- Bopp. Large amounts of organic material have been detected on comets, such as Halley and Hale- Bopp. They also believe that much of the water on Earth arrived from comet collisions. They also believe that much of the water on Earth arrived from comet collisions.

Meteorites Many of the meteorites that survive to hit the Earth also contain organic compounds, including amino acids. Many of the meteorites that survive to hit the Earth also contain organic compounds, including amino acids. Both meteorites and comets show that amino acids can survive interstellar space. Both meteorites and comets show that amino acids can survive interstellar space.

Interesting Timeline Earth is 4.6 billion years old. Earth is 4.6 billion years old. That is too much time to really fathom. That is too much time to really fathom. As an analogy, let’s instead say that the Earth is only 46 years old. As an analogy, let’s instead say that the Earth is only 46 years old. We have no record at all of the first 10 years. We have no record at all of the first 10 years. Life originated at least 35 years ago. Life originated at least 35 years ago. Only about six years ago did life begin to flourish. Only about six years ago did life begin to flourish.

Interesting Timeline Life came ashore 4 years ago. Life came ashore 4 years ago. Plants and animals began to flourish 2 years ago. Plants and animals began to flourish 2 years ago. Dinosaurs reached their peak only 1 year ago, only to die four months later. Dinosaurs reached their peak only 1 year ago, only to die four months later. Humanlike beings only became predominant last week. Humanlike beings only became predominant last week. The last ice age was only a few days ago. The last ice age was only a few days ago. Homo sapiens did not emerge until four hours ago. Homo sapiens did not emerge until four hours ago.

Interesting Timeline Agriculture was invented within the last hour. Agriculture was invented within the last hour. The Renaissance and modern sciences came about just three minutes ago! The Renaissance and modern sciences came about just three minutes ago!