Free to follow every thread. No paywall, no dead ends.
Land: the story on HearLore | HearLore
Land
Scientists date the earliest material found in the Solar System to 4.568 billion years ago. Earth itself formed by accretion around this same time. A solar nebula partitioned a volume out of a molecular cloud by gravitational collapse. This process began to spin and flatten into a circumstellar disc. Planets grew from this disc in tandem with the Sun. The primordial Earth's assembly took between 10 million and 100 million years. By 4.4 billion years ago, the primordial Earth had fully formed.
Volcanic activity and outgassing created Earth's early atmosphere and oceans. Water vapour condensed to form the first oceans. Asteroids, protoplanets, and comets delivered additional water and ice. Atmospheric greenhouse gases kept these oceans from freezing while the new Sun was only at 70% luminosity. By 4.2 billion years ago, Earth's magnetic field established itself. This field prevented the atmosphere from being stripped away by the solar wind.
Earth's crust formed when the molten outer layer cooled to create a solid mass. Accumulated water vapour began to act in the atmosphere once land became capable of supporting life. Biodiversity evolved over hundreds of millions of years. Mass extinctions punctuated this expansion. Two models explain land mass growth today. One suggests steady growth to present-day forms. The other proposes rapid growth early in history followed by long-term stability.
Mountains And Shifting Plates
Plate tectonics drives the movement of continental plates over the mantle. Alfred Wegener first hypothesized continental drift in 1912. Researchers developed his idea throughout the 20th century into the accepted theory of plate tectonics. A place where two tectonic plates meet is called a plate boundary. Different geological phenomena occur across different kinds of boundaries.
Divergent plate boundaries usually show seafloor spreading. Convergent or transform plate boundaries feature subduction zones. Earthquakes and volcanic activity are common in all types of boundaries. Volcanic activity refers to any rupture in Earth's surface where magma escapes as lava. The Ring of Fire contains two-thirds of the world's volcanos. It also holds over 70% of Earth's seismological activity.
Mountain belts form through orogenesis resulting from plate tectonics. Where a plate at a convergent boundary pushes one plate above another, mountains rise. Collisional events push Earth's crust upwards. Subductional events push crust into the mantle causing it to melt and solidify. Plateaus are high plains raised sharply above surrounding areas on at least one side. They create steep cliffs or escarpments. Volcanic upwelling of magma can create these features. Erosion by water, glaciers, or wind also forms them.
When did Earth form and how long did its assembly take?
Earth formed by accretion around 4.568 billion years ago, with the primordial Earth's assembly taking between 10 million and 100 million years to complete.
What created Earth's early atmosphere and oceans according to scientists?
Volcanic activity and outgassing created Earth's early atmosphere and oceans while asteroids, protoplanets, and comets delivered additional water and ice.
Who first hypothesized continental drift in 1912 and what is it called today?
Alfred Wegener first hypothesized continental drift in 1912 before researchers developed his idea throughout the 20th century into the accepted theory of plate tectonics.
How much precipitation do deserts receive per year and what percentage of land area do they cover?
Deserts have an arid climate receiving less than 25 centimeters of precipitation per year and make up around one fifth of Earth's land area.
When did humans cross from Siberia to Alaska and settle in the Americas?
Fourteen thousand years ago some crossed the Ice Age land bridge from Siberia to Alaska and then moved southbound to settle in the Americas.
What percentage of irrigated lands are affected by salinization and how does this impact productivity?
Salinization affects at least 20% of all irrigated lands making them less productive through chemical imbalances caused by human activity.
A biome is an area characterized by its vegetation, soil, climate, and wildlife. Five major land biomes exist today: grasslands, forests, deserts, tundras, and freshwater. Deserts have an arid climate receiving less than 25 centimeters of precipitation per year. They make up around one fifth of Earth's land area. These zones appear on every continent and can be very hot or cold.
Most erosion in deserts occurs during violent thunderstorms. Running water causes flash floods that reshape the landscape. Desertification spreads arid areas due to excessive deforestation and overgrazing. Tundra is a biome where tree growth hinders frigid temperatures and short growing seasons. Arctic tundra, alpine tundra, and Antarctic tundra represent different regional types.
A forest is an area dominated by trees. The United Nations Food and Agriculture Organization defines a forest as land spanning more than 0.5 hectares with trees higher than 5 meters. Canopy cover must exceed 10 percent. Forests include rainforests, deciduous forests, and boreal forests. Grasslands are areas where vegetation is dominated by grasses. Sedge and rush also grow there alongside legumes like clover. Savannas are grasslands with occasional scattered trees.
The Human Journey Across Land
Humans have traveled for business, pleasure, discovery, and adventure since ancient times. Land navigation involves progressing through unfamiliar terrain using maps, compasses, or satellite systems. Natural landmarks guide travelers across vast distances. Table Mountain in South Africa stands out from its environment. Mount Ararat in Turkey serves as another example. The Grand Canyon in the United States marks a clear path. Uluru in Australia and Mount Fuji in Japan act as enduring guides.
Two major eras of exploration occurred in human history. One era saw divergence as humans moved out of Africa. They settled in new lands developing distinct cultures in isolation. Early explorers settled in Europe and Asia. Fourteen thousand years ago some crossed the Ice Age land bridge from Siberia to Alaska. They then moved southbound to settle in the Americas. These cultures remained ignorant of each other's existence for millennia.
A second period began roughly 10,000 years ago. It marked increased cross-cultural exchange through trade and exploration. Major trade routes existed on land such as the Silk Road linking East Asia with Europe. The Amber Road transferred amber from Northern Europe to the Mediterranean Sea. Central Asia became the economic center during the Middle Ages. Luxury goods were commonly traded throughout Europe.
Farming And Urban Expansion
For more than 10,000 years humans have engaged in activities like hunting, foraging, and agriculture. The Neolithic Revolution spread agriculture around the world. Human land use significantly altered terrestrial ecosystems by 3000 years ago. From 1750 onward usage increased at an accelerating rate due to the Industrial Revolution. Rapid population growth created greater demand for natural resources.
A third of Earth's land surface is used for agriculture. Estimated figures show vast areas dedicated to cropland and pastureland. When land clears for agriculture native flora and fauna disappear. Excessively high agricultural use stems from poor management practices. Food waste and meat-heavy diets drive this expansion further. Urbanization shifted the global population from rural to urban living in 2007.
Urban areas make up less than 3 percent of Earth's land area yet they displace fertile soil. People living in cities depend on food produced outside their boundaries. This creates demand driving land use change well beyond city limits. Mining extracts minerals from the ground using various methods. Evidence dates back to 3000 BCE in Ancient Egypt. Iron ore, coal, and gemstones remain important extracted materials today.
Soil Health And Global Threats
Land degradation reduces biological or economic productivity through human activity. Humans have altered more than three-quarters of ice-free land through habitation. Soil degradation occurs via physical processes like erosion and chemical imbalances such as salinization. Salinization affects at least 20% of all irrigated lands making them less productive. Deliberate tillage disrupts biological processes leading to nutrient loss.
Desertification spreads arid areas due to natural processes or human activities. Deforestation and improper land management accelerate this spread globally. Ground pollution involves soil contamination via hazardous waste or litter. Landfills can span thousands of acres like the Apex Regional landfill in Las Vegas. Water pollution contaminates non-oceanic hydrological features including lakes and rivers.
Biodiversity loss threatens the variety and variability of life. Agriculture converts land for crops at a very high rate particularly in the tropics. Pesticides and herbicides negatively impact local species health. Ecosystems divide and degrade by infrastructure development outside urban zones. Earth currently undergoes its sixth mass extinction known as the Holocene extinction. This event proves irreversible so far due to human activities pushing beyond planetary boundaries.