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.

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.

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!

A placebo is a medicine or treatment intended to appear genuine, but actually have no pharmaceutical effect, such as inert sugar pills. The placebo effect is a genuine psychobiological phenomenon in which the mere expectation of improvement from a placebo can lead to some actual physiological changes. Modern studies find that placebos can affect some outcomes such as pain and nausea, but otherwise do not generally have important clinical effects. There is also the effect called a nocebo effect. The nocebo effect is falling ill simply by consciously or subconsciously anticipating a harmful event. Both placebo and nocebo effects are presumably psychogenic but can induce measurable changes in the body.

Hormones play a very large part in the physiological processes of the body. The endocrine system consists of numerous glands throughout the body that produce and secrete hormones of diverse chemical structure, including peptides, steroids, and neuroamines. The nervous system and the endocrine system are linked in a process known as neuroendocrine integration. The neuroendocrine system is the mechanism by which the hypothalamus maintains homeostasis, regulating reproduction, metabolism, eating and drinking behaviour, energy utilization, osmolarity and blood pressure. Neuroendocrinology is the branch of biology (specifically of physiology) which studies the interaction between the nervous system and the endocrine system; i.e. how the brain regulates the hormonal activity in the body.

Meganeuropsis permiana was considered the largest insect of all time, it was a dragonfly relative with an estimated wingspan of around 710 mm (28 in). It existed before the dinosaurs, during the Artinskian age of the Permian period, 290.1–283.5 million years ago. There are several theories as to why insects were so big during this time. One theory was that oxygen levels in the atmosphere were significantly higher than today, although there is some controversy regarding this theory. Another theory was that insects at the time were at the top of the food-chain, with few predators.

In psychology, cognitive dissonance is a phenomenon where people unknowingly or subconsciously hold fundamentally conflicting cognitions (mental processes). Being confronted by situations that create this dissonance or highlight these inconsistencies can cause stress (discomfort) and motivates change in their thoughts or actions to reduce this dissonance. Persons who experience internal inconsistency tend to become psychologically uncomfortable and are motivated to reduce the cognitive dissonance in several ways, such as: rationalization (justifying the behavior), using a just-world fallacy, using selective perception (ignoring some info), or avoiding information (resulting in confirmation bias).

Scientists studying dinosaur fossils are able to tell with some certainty the color patterns the dinosaur exhibited. The Microraptor, for example, likely had shiny iridescent black feathers (similar to a crow) used for signaling. Another example is the Borealopelta, which had a reddish-brown countershaded pattern that was used for camouflage. Sinosauropteryx had a raccoon-like “mask” around the eyes and banded patterns on its tail. To infer these colors, scientists have studied well preserved melanosomes found in fossilized skin and feathers. Scientists study the shape, color, and nanostructures of the melanosomes.

The study of Biomimicry (or Biomimetics) looks at elements and systems of nature and attempts to replicate them to solve complex human problems. This is applied in fields from materials science to architecture. Some examples of biomimicry include: How the tiny hooks on bur fruits inspired Velcro. Leonardo da Vinci’s flying machine inspired by the structure of bat wings. Shark skin is being studied to improve movement through water. Geckoes climbing ability on walls and ceilings due to their micrometer-scale hair-like setae on their feet have inspired special adhesive tape. Colorful Morpho butterfly wings have inspired display technology. There are many more examples in this fascinating field of study. https://en.wikipedia.org/wiki/Biomimetics

The astronomical unit (or AU) is defined as approximately the mean distance between the Earth and the Sun. It is defined as 149,597,870,700 meters or approximately 93 million miles. At this distance, it takes slightly more than 8 minutes and 19 seconds for light to travel between the Sun and the Earth (or 1 AU). AU is one method of measuring distances within the Solar System. Light-Seconds (the distance that light travels in free space in one second, such as 1.3 light-seconds between the Earth and Moon) is also used… while Parsecs are used for large distances to astronomical objects outside the Solar System. One Parsec is 206,265 AU’s or 19.2 trillion miles.

The double-slit experiment is an important physics demonstration of how light and matter can exhibit behavior associated with both classical particles and classical waves. In the experiment, the wave nature of light causes the light waves passing through two slits to interfere, producing bright and dark bands on the screen – a result that would not be expected if light consisted of classical particles. However, the light is always found to be absorbed at the screen at discrete points, as individual particles (not waves). The more mind-boggling part? When scientists placed detectors to determine which slit an electron passed through (as electrons exhibit the same effects as photons) the interference pattern disappears. This “which way” experiment demonstrated the concept in quantum mechanics called wave-particle duality, in which photons or electrons exhibit particle or wave properties according to the experimental circumstances.

Origin of life research is the study of how life came to be as a transition from non-life to life in the vastly different early Earth environment. What happened 4 billion years ago before LUCA? Abiogenesis is the scientific hypothesis for origin of life explaining a natural process by which life arises from non-living matter, such as simple organic compounds. Abiogenesis asks: how did pre-life chemical reactions give rise to life? Ideas such as RNA World hypothesis, “metabolism-first” hypotheses, the 1952 Miller–Urey experiment, Warm Little Pond, and Primordial Soup, seek to answer this question. Panspermia is the idea that life may have originated elsewhere in the universe and came to Earth: amino acids (the building blocks necessary for life) have been found in meteorites, comets, asteroids, and star-forming regions of space.

The adult human brain weighs on average about 1.2–1.4 kg (2.6–3.1 lb) which is about 2% of the total body weight. Although the human brain represents only 2% of the body weight, it receives 15% of the cardiac output from the heart, 20% of total body oxygen consumption, and 25% of total body glucose utilization. The brain consumes up to 20% of the energy used by the human body, more than any other organ. Brain metabolism normally relies upon blood glucose as an energy source, but during times of low glucose (such as fasting, endurance exercise, or limited carbohydrate intake), the brain uses ketone bodies for fuel with a smaller need for glucose. Bonus fact: The adult human brain is estimated to contain 86±8 billion neurons.

A neutron star is so dense that one teaspoon of its material would have a mass over 5,500,000,000 tonnes (5.5 billion), about 900 times the mass of the Great Pyramid of Giza (often cited as 5.9 million tons / 5.3 million tonnes). At the extraordinarily high densities of neutron stars, ordinary matter is squeezed to nuclear densities. All of that matter is packed into a radius on the order of 10 kilometers (6 miles). Bonus fact: There are a number of sub-types of neutron stars, such as pulsars, magnetars, both pulsars and magnetars, x-ray pulsars, and more.

400 million years ago, in the Devonian period, cartilaginous fishes such as primitive sharks became more numerous. The first tree dates to about 385 million years ago, and the Dinosaur Age started 252 million years ago, making sharks older than trees and dinosaurs. One galactic year (the duration of time required for the Sun to orbit once around the center of the Milky Way Galaxy) is approximately 225 million Earth years, meaning that sharks have been around for two complete galactic years. Bonus fact: Sharks and rays rely on electrolocation to detect the electromagnetic field of living things nearby. The shark has the greatest electrical sensitivity of any animal. Sharks can find prey hidden in sand by detecting the electric fields.

Evidence is mounting that loggerhead turtles use a form of navigation termed Magnetoreception. This allows them to sense the Earth’s magnetic field. It has been observed that young loggerhead turtles inherit a magnetic map and magnetic compass sense that guides their first transoceanic migration. The turtles change their migration direction due to the magnetic fields in key ocean areas. Most sea turtle species migrate over significant distances to nesting or foraging grounds, some even crossing entire ocean basins.

The electric eel can stun their prey by delivering a shock of up to 860 volts. According to one study, the shocks from leaping electric eels are powerful enough to drive away animals as large as horses by activating the nociceptor sensory neurons in the horse. The electric eel stacks some 6,000 electrocytes in series (longitudinally) in its main organ; the organ contains some 35 such stacks in parallel, on each side of its body. The eel can either use its electrical discharge to locate pray (electrolocate) or to stun them. It is said that Volta was inspired by the electric eel in inventing the voltaic pile, the first electrical battery that could continuously provide an electric current to a circuit. Volta does casually mention the electric eel in an essay.

Lightning can heat the air it passes through to temperatures of about 30,000 °C (54,000 °F). That is regarded as 5 times hotter than the surface of the sun. The discharge process, or return stroke, of the lightning is the most luminous part where the electric current moves through the channel. One observation found that the rate at which the return stroke current traveled was around 100,000 km/s (or one-third the speed of light). Global monitoring indicates that lightning on Earth occurs at an average frequency of approximately 44 (± 5) times per second.

In the 17th century, Isaac Newton discovered that prisms could split up white light into a spectrum of colors. He also showed that the spectrum could be recombined to recreate white light. Newton was the first to use the word spectrum in describing his experiments. Today we call the band of the electromagnetic spectrum that is visible to the human eye the visible spectrum. We call the colors such as red, orange, yellow, green, cyan, blue, and violet the spectral colors and they correspond to narrow bands of wavelengths. Light that has longer wavelengths than the spectral colors are called ultravoilet, while light that has shorter wavelengths are called infrared. Humans cannot generally see ultraviolet or infrared, but there are some animals that can. Most animals evolved to have a visible range that matches what is called the optical window, which is the range of light that can pass through the atmosphere.

Neptune’s winds in the equatorial region have speeds of around 1,200 km/h (750 mph), with some storm systems having wind speeds that reach up to 2,100 km/h (1,304 mph) making them near-supersonic. For comparison, the fastest wind gust ever recorded on Earth was 408 km/h (253 mph). The average airliner flies at around 500 mph. The speeds of the winds on Neptune show just how different weather systems can be on other planets, and highlights another way that Earth is rare in its habitability.