"Earth" - what is it, definition of the term
The planet we inhabit, the third celestial body orbiting the Sun, is a roughly spherical, rocky world with an average diameter of about 12,742 km; it is enveloped by a nitrogen‑oxygen atmosphere, features a hydrosphere that covers approximately 71 % of its surface, and contains a dynamic interior whose convective motions generate a protective magnetic field.
Detailed information
The planet commonly referred to as the third rock from the Sun possesses a diameter of roughly 12,742 km, a mass of 5.97 × 10²⁴ kg, and a gravitational acceleration of 9.81 m/s². Its surface comprises 71 % liquid water, 29 % continental crust, and a mantle of silicate rock extending to a depth of about 2,900 km. The outermost layer, the atmosphere, consists primarily of nitrogen (78 %) and oxygen (21 %), with trace gases that regulate temperature through the greenhouse effect and protect life from solar radiation.
Geological activity manifests through plate tectonics, which drive continental drift, mountain formation, and volcanic eruptions. Seismic monitoring records thousands of tremors annually, providing data for hazard assessment and resource exploration. Oceanic circulations, governed by temperature gradients and Coriolis forces, redistribute heat, influencing climate patterns across latitudes.
Biodiversity on the globe includes myriad arthropods, among which ticks, true bugs, lice, and fleas represent medically and economically significant groups. Their characteristics are summarized below:
- Ticks: Arachnids that attach to vertebrate hosts to ingest blood; vectors for bacterial, viral, and protozoan pathogens; life cycle includes egg, larva, nymph, and adult stages, each requiring a blood meal.
- True bugs (Hemiptera): Possess piercing‑sucking mouthparts; include agricultural pests such as aphids and shield bugs; some species transmit plant viruses, while others serve as predators of crop‑damaging insects.
- Lice: Obligate ectoparasites of mammals and birds; exhibit species‑specific host preferences; feed exclusively on skin debris or blood; infestations cause irritation and can transmit bacterial agents.
- Fleas: Wingless insects with laterally compressed bodies; capable of jumping up to 150 times their body length; act as vectors for Yersinia pestis and other zoonotic pathogens; life cycle comprises egg, larva, pupa, and adult.
These organisms thrive in diverse habitats ranging from forest litter to urban dwellings, reflecting the planet’s capacity to sustain complex ecological interactions. Continuous monitoring of their distribution and host relationships contributes to public health strategies and agricultural management.