CEN 511: Recent Discoveries in Astronomy

1. Find some web pages examining the earliest forms of life deduced from genetic evidence. What is the most up-to-date idea for the bottom of the tree of life? For example, is Archaea now believed to pre-date Eurcarya and Bacteria, or are both Archaea and Bacteria thought to be more primitive than Eucarya?
2. The branch of life involving cells with nuclei, regions containing genetic information separated from the rest of the cell by a membrane, is called what?
3. Suppose a rock is formed 4.47 billion years ago containing ⁴⁰K and ²³⁸U nuclei in equal numbers. Today, which nucleus is more abundant in the rock, and by what factor?
4. Do a web search to discover the biological half-life of tritium (³H), which is radioactive, in the human body. The biological half-life is the time it takes half the tritium in water you drink to be eliminated as waste or in respiration.
   1. In this same time period, what fraction of ³H will decay by radioactivity?
   2. This small fraction means that you would have to drink a large quantity of tritium for it to be harmful. Given this, do you think the tens of millions of dollars Brookhaven National Laboratory was forced to spend to clean up a leak of a few ounces of tritium-contaminated water from a reactor into the ground was money well spent? Note that only tritium that is ingested is harmful; the radiation from tritium cannot penetrate the layer of dead skin on the outside of your body.
5. A microfossil is a microscopic fossil, the remnant of a microorganism. What constitutes a chemofossil, which is a less direct piece of evidence? Find different examples by searching on the web. For example, some of the evidence cited for life in conjunction with some Martian meteorites were chemofossils.
6. Compare the geologic chart to a 24-hour clock running from early morning to midnight. If the Earth came into existence at 12:01 AM, at what time did life form? At what time did the Cambrian explosion occur? At what times did dinosaurs evolve and then become extinct? At what time did humans evolve?