Box Carl Richard Woese

Carl Woese is an American molecular microbiologist, who, in 1977, on the basis of RNA evidence, split the domain Bacteria into two domains, the Bacteria and the Archaea. This view gained acceptance only slowly, and there was hostility from some biologists and even from some non-scientists. Even today there is a small minority that does not accept this split. This is characteristic of revolutions in science - as evidence piles up showing the accepted model or theory to be inadequate, a fairly...

Obtaining stellar spectra

How are stellar spectra of the sort in Figure 10.9 obtained In order to obtain a star's spectrum, the light collected from the star by a telescope has to be passed through a device that sends different wavelengths into FIGURE 10 12 A star in an orbit inclined at an angle with respect to the plane of the sky. FIGURE 10.13 A dispersing device separating three absorption lines, with (below) the image intensity obtained by scanning across these lines. FIGURE 10.13 A dispersing device separating...

Searches At Microwavelengths

Figure 14.2 is a spectrum of the power received from the cosmos over a range of frequencies that encompasses microwaves. It illustrates some of the reasons why microwaves have been favored for SETI. Three distinct components of the overall spectrum are shown. One shows the power in the radiation that we typically receive from the Galaxy. This is due to what is called synchrotron radiation from electrons as they move through the magnetic fields that pervade our Galaxy. It declines steeply as...

Adaptation

The principle of adaptation in a version relevant to this section states that a species will have sense organs and an external form that is adapted to its environment. This means that two similar environments, whether on the same planet, on two different planets in the same planetary system, or on two planets in different planetary systems, would have creatures that display similarities in their sense organs and external form. This principle enables us to make an educated guess about what...

Evidence of photosynthesis

The most readily detectable spectral feature of our biosphere at these wavelengths is the red edge at near infrared wavelengths around 0.8 micrometers, produced by green vegetation. This is shown in Figure 13.8. This is a reflectance spectrum. Take care not to confuse it with the emission spectra we have been considering before. In a reflectance spectrum the vertical axis shows the fraction of the radiation from some separate radiation source (such as the Sun) that is being reflected by the...

Ascending the tree of life

Time advances as we move up each branch. The first branching above the last common ancestor shows the Bacteria dividing from the Archaea. It is not known which of these two domains of life extend towards the last common ancestor. Some of the branching dates in Figure 5.1 are known. These have been obtained from fossils embedded in or between radiometrically dated rocks. For example, plants appeared by about 470 Myr ago. The first animal fossils date back to about 575 Myr ago. Other branching...

The solar spectrum and electromagnetic radiation

To further lay a basis for later chapters, you need to know something about what is called the electromagnetic spectrum. The solar spectrum is a good way to introduce the essential ideas. FIGURE 2.7 The Sun about 7,000 Myr from now, when it will be a fully fledged red giant, and the Solar System will be uninhabitable. FIGURE 2.7 The Sun about 7,000 Myr from now, when it will be a fully fledged red giant, and the Solar System will be uninhabitable. When you look at the Sun, our human eyes are...

Orbits And Sizes

Fig Eight Planet

Figure 2.1 shows a plan view of the orbits of the eight planets around our star, the Sun. The planets themselves, and the Sun, which is far larger than any planet, are too small to be shown on this scale. The scales are marked on the Figure. The upper scale is 150 million kilometers (1 kilometer (km) 0.621 miles). This is very nearly the same as the average distance between the Earth and the Sun, which is called the astronomical unit, abbreviated to AU, and equal to 149.6 million km. The AU is...

Exotic possibilities for interstellar travel

Wormholes are short cuts through spacetime, which is the four dimensional construct in relativity consisting of the three space dimensions and time. A wormhole is a channel that permits travel from one point in spacetime to another without us having to travel through ordinary space. This permits superluminal (faster than light) travel. It also permits travel back in time, which would lead to all sorts of problems - any slight alteration in history made by a time traveler could alter the world...

Telescopes in space

Space has the advantage of avoiding all the problems posed by the Earth's atmosphere, which can only be partially compensated at ground level. The best known space telescope is probably NASA's Hubble Space Telescope (Figure 8.8), FIGURE 8.8 NASA's Hubble Space Telescope, launched in 1990, and now showing signs of old age. Unless its orbit is boosted it will re-enter the Earth's atmosphere in 2010 or soon after. It has a 2.4 meter diameter mirror. (NASA) FIGURE 8.8 NASA's Hubble Space Telescope,...

RNA and DNA

These are large, complex organic compounds that are at the heart of protein synthesis, and are central to the processes by which organisms reproduce themselves. RNA - ribonucleic acid - is a long molecule, another polymer. A typical segment is shown in Figure 3.5. The spine consists of a string of identical units. Each unit contains an organic molecule called ribose - a member of the sugar family, a family of compounds of C, H, and O. This is attached to a phosphate -compounds of P, O, and a...

The last common ancestor

Consider the example of the isotope of the chemical element rubidium, Rb. This element has 37 protons in its nucleus. It has just one stable (nonradioactive) isotope with a nucleus containing 48 neutrons, making 85 nuclear particles in total. It is thus called rubidium-85, written in shorthand as 85Rb. Rubidium has four radioactive isotopes, the most abundant of these being 87Rb i.e., 50 neutrons in the nucleus. This nucleus emits an electron. As a result the number of neutrons in its nucleus...

A fundamental limit to the sharpness of telescope images

Figure 8.2(a) is a simplified diagram of a reflecting telescope. This is the sort in which the main optical element that collects and focuses the radiation from a distant object is a concave mirror, rather like a shaving mirror. Whereas lenses are still used in cameras, most binoculars, and some small telescopes, the larger telescopes use a concave mirror because compared to a large lens this is much cheaper and will generally have superior performance. The diameter of the main mirror is...

The Discovery Of Exoplanetary Systems

In 1992, after decades of disappointment and false hope, the first exoplanets were discovered. The US astronomers Alex Wolszczan and Dale Frail announced that they had detected two planets in orbit around a rare type of star called a pulsar. Each planet had a mass just a few times that of the Earth. The claim that a pulsar had planets was greeted with considerable surprise by other astronomers, but it has withstood further investigation. The surprise stems from the way that a pulsar is formed,...

Box Astronomical units of distance

In our everyday lives the kilometer (0.621 miles) is a convenient unit of distance. The average adult can easily walk a kilometer (km) in about 15 minutes. It also suits the sizes of planetary bodies - the Earth has an equatorial diameter of 6,378 km. In the Solar System the astronomical unit (AU) is a convenient unit, being the average distance of the Earth from the Sun (149.6 million km). But even the nearest star (Proxima Centauri) is 267,000 AU away. Clearly a bigger unit of distance would...

Convergent evolution

Adaptation is intimately connected with convergent evolution. This is when two species with ancestors in different parts of the tree of life Section 5.1 have evolved to look or behave like each other to cope with some aspect of their environment. There are many examples of convergent evolution on Earth. One example is humming birds and a moth called the hummingbird-hawkmoth Figure 15.5 . These have similar sizes, body shape, and feeding by FIGURE 15.5 A hummingbird-hawkmoth. James McGlasson...

Transit Photometry

If the orbit of a planet is presented to us sufficiently close to edgewise, then, once per orbit, for a small fraction of its orbital period, the planet will pass between us and the star - the planet will be observed in transit. The planet emits negligible radiation at visible wavelengths, so the visible radiation we receive from the star during the transit is reduced. Even at infrared wavelengths, where the planet emits radiation, the brightness of the planet is far less than that of the area...