A keystone species is a species that has a disproportionately large effect on its natural environment relative to its abundance. Without keystone species, the ecosystem would be dramatically different or cease to exist altogether. The role that a keystone species plays in its ecosystem is analogous to the role of a keystone in an arch. An ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of biomass or productivity. Some examples of keystone species are: Sea otters that protect kelp forests from damage by sea urchins. Wolves prevent a single species from becoming dominant. Beavers are known as ecosystem engineers, and Elephants destroy trees, making room for the grass species and creating habitat for various small animal species.

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The speed of light is exactly 299,792,458 metres per second, denoted as c – a universal physical constant. This is equivalent to 1 billion kilometres per hour, or 700 million miles per hour. The speed of light in vacuum is the upper limit for the speed at which information, matter, or energy can travel through space. c is not just the speed of light, it is finite, and is considered a universal speed limit for all matter or information. This limit arises directly from the structure of space-time, as described by Einstein’s special relativity. Nothing with mass can travel as fast or faster than the speed of light according to relativity. All forms of electromagnetic radiation, including visible light, travel in vacuum at the speed c as do massless particles and field perturbations, such as gravitational waves.

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Trace evidence occurs when objects make contact, and material is transferred. This type of evidence may not even be visible to the naked eye and requires specific tools and techniques to be located and obtained. Microscopic hair and dead skin cells can be collected, as well as droplets of blood, saliva, or semen for DNA evidence. Fingerprints can be identified but may also leave secretions, skin oils and dead cells which show chemicals and metabolites present in the body at the time. Forensic identification is the application of forensic science and technology to identify specific objects from the trace evidence they leave.

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The body’s ability to maintain homeostasis is a critical function. In biology, homeostasis is the state of steady internal physical and chemical conditions maintained by living organisms. The body has many aspects that it maintains using homeostatic control mechanisms including: optimal temperature, fluid balance, cerebrospinal fluid, pH of extracellular fluid, concentrations of oxygen, carbon dioxide, sodium, potassium, calcium ions, copper, iron levels, blood sugar levels, plasma pH, blood oxygen content as well as blood pressure. These levels are kept within certain pre-set limits (homeostatic range) even during changes in the environment, diet, or level of activity.

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The Great Oxygenation Event (GOE) was a time interval during the Earth’s Paleoproterozoic era (2,500 to 1,600 million years ago) when the Earth experienced a rise in the concentration of free oxygen from practically none. The GOE is inferred to have been caused by cyanobacteria, which evolved chlorophyll-based photosynthesis that releases dioxygen as a waste byproduct of water photolysis. Scientists believe the GOE may have caused an extinction of many early Earth organisms, including the retinal using (Purple Earth hypothesis) organisms that lived during that time. The adaptation of surviving archaea (leading to mitochondria) may have led to the rise of eukaryotic organisms and eventually multicellular life-forms. So Earth may have been purple before, and we’re only here thanks to cyanobacteria!

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