Quick Links
Quick Links
UPSC Exams
Latest Update
Coaching
UPSC Current Affairs
Syllabus
UPSC Notes
Previous Year Papers
UPSC Mains Previous Year Question Papers Last 25 Years UPSC Prelims Question Papers Last 10 Years UPSC Question Papers UPSC CSE Prelims 2025 Question Paper UPSC Mains 2024 Model Answers UPSC 2024 Question Papers UPSC 2023 Question Papers UPSC 2022 Question Papers UPSC 2021 Question Papers UPSC 2020 Question Papers UPSC 2019 Question Papers UPSC 2018 Question Papers UPSC 2017 Question Papers UPSC 2016 Question Papers UPSC 2015 Question Papers UPSC 2014 Question Papers UPSC CSAT Question Papers UPSC IFS Previous Year Paper UPSC Assistant Labour Commissioner Previous Question Year Papers UPSC Combined Geo Scientist Previous Year Paper UPSC APFC Previous Year Question Papers UPSC CMS Previous Year Question Paper UPSC EPFO Previous Year Paper UPSC Air Safety Officer Previous Year Papers UPSC SO Steno Previous Year Paper UPSC IES ISS Previous Year Question Papers
Mock Tests
UPSC Editorial
Bilateral Ties
Albania India Relations India Algeria Relations Andorra India Relations India Angola Relations India Antigua Barbuda Relations India Argentina Relations Austria India Relations India Azerbaijan Relations Bahamas India Relations India Bahrain Relations Barbados India Relations India Belarus Relations Belgium India Relations Belize India Relations Benin India Relations Bolivia India Relations India Bosnia Herzegovina Relations India Botswana Relations Brazil India Relations Brunei India Relations Bulgaria India Relations Burundi India Relations Cabo Verde India Relations India Cambodia Relations India Cameroon Relations Canada India Relations India Cayman Islands Relations India Central African Republic Relations India Chad Relations Chile India Relations India Colombia Relations India Comoros Relations India Democratic Republic Of The Congo Relations India Republic Of The Congo Relations India Cook Islands Relations India Costa Rica Relations India Ivory Coast Relations India Croatia Relations India Cyprus Relations India Czech Republic Relations India Djibouti Relations India Dominica Relations India Dominican Republic Relations India Ecuador Relations India El Salvador Relations India Equatorial Guinea Relations India Eritrea Relations Estonia India Relations India Ethiopia Relations India Fiji Relations India Finland Relations India Gabon Relations India Gambia Relations India Georgia Relations Germany India Relations India Ghana Relations India Greece Relations India Grenada Relations India Guatemala Relations India Guinea Relations India Guinea Bissau Relations India Guyana Relations India Haiti Relations India Holy See Relations India Honduras Relations India Hong Kong Relations India Hungary Relations India Iceland Relations India Indonesia Relations India Iran Relations India Iraq Relations India Ireland Relations India Jamaica Relations India Kazakhstan Relations India Kenya Relations India Kingdom Of Eswatini Relations India Kiribati Relations India Kuwait Relations India Kyrgyzstan Relations India Laos Relations Latvia India Relations India Lebanon Relations India Lesotho Relations India Liberia Relations Libya India Relations Liechtenstein India Relations India Lithuania Relations India Luxembourg Relations India Macao Relations Madagascar India Relations India Malawi Relations India Mali Relations India Malta Relations India Marshall Islands Relations India Mauritania Relations India Micronesia Relations India Moldova Relations Monaco India Relations India Montenegro Relations India Montserrat Relations India Morocco Relations Mozambique India Relations India Namibia Relations India Nauru Relations Netherlands India Relations India Nicaragua Relations India Niger Relations India Nigeria Relations India Niue Relations India North Macedonia Relations Norway India Relations India Palau Relations India Panama Relations India Papua New Guinea Relations India Paraguay Relations Peru India Relations India Philippines Relations Qatar India Relations India Romania Relations Rwanda India Relations India Saint Kitts And Nevis Relations India Saint Lucia Relations India Saint Vincent And Grenadines Relations India Samoa Relations India Sao Tome And Principe Relations Saudi Arabia India Relations India Senegal Relations Serbia India Relations India Sierra Leone Relations India Singapore Relations India Slovak Republic Relations India Slovenia Relations India Solomon Islands Relations Somalia India Relations India South Sudan Relations India Spain Relations India Sudan Relations Suriname India Relations India Sweden Relations India Syria Relations India Tajikistan Relations Tanzania India Relations India Togo Relations India Tonga Islands Relations India Trinidad And Tobago Relations India Tunisia Relations India Turkmenistan Relations India Turks And Caicos Islands Relations India Tuvalu Relations India Uganda Relations India Ukraine Relations India Uae Relations India Uruguay Relations India Uzbekistan Relations India Vanuatu Relations India Venezuela Relations India British Virgin Islands Relations Yemen India Relations India Zambia Relations India Zimbabwe Relations
Books
Government Schemes
Production Linked Incentive Scheme Integrated Processing Development Scheme Rodtep Scheme Amended Technology Upgradation Fund Scheme Saathi Scheme Uday Scheme Hriday Scheme Samagra Shiksha Scheme India Nishta Scheme Stand Up India Scheme Sahakar Mitra Scheme Mdms Mid Day Meal Scheme Integrated Child Protection Scheme Vatsalya Scheme Operation Green Scheme Nai Roshni Scheme Nutrient Based Subsidy Scheme Kalia Scheme Ayushman Sahakar Scheme Nirvik Scheme Fame India Scheme Kusum Scheme Pm Svanidhi Scheme Pmvvy Scheme Pm Aasha Scheme Pradhan Mantri Mahila Shakti Kendra Scheme Pradhan Mantri Lpg Panjayat Scheme Mplads Scheme Svamitva Scheme Pat Scheme Udan Scheme Ek Bharat Shresth Bharat Scheme National Pension Scheme Ujala Scheme Operation Greens Scheme Gold Monetisation Scheme Family Planning Insurance Scheme Target Olympic Podium Scheme
Topics
NASA Space Missions
NASA Mercury-Redstone 3 (Freedom 7) Mission NASA Mercury-Redstone 4 (Liberty Bell 7) Mission NASA Mercury-Atlas 6 (Friendship 7) Mission NASA Mercury-Atlas 7 (Aurora 7) Mission NASA Mercury-Atlas 8 (Sigma 7) Mission NASA Mercury-Atlas 9 (Faith 7) Mission NASA Gemini 3 Mission NASA Gemini 4 Mission NASA Gemini 5 Mission NASA Gemini 7 Mission NASA Gemini 8 Mission NASA Gemini 9 Mission NASA Gemini 10 Mission NASA Gemini 11 Mission NASA Gemini 12 Mission NASA Apollo 1 (AS‑204) Mission NASA Apollo 7 Mission NASA Apollo 8 Mission NASA Apollo 9 Mission NASA Apollo 10 Mission NASA Apollo 11 Mission NASA Apollo 12 Mission NASA Apollo 13 Mission NASA Apollo 14 Mission NASA Apollo 15 Mission NASA Apollo 16 Mission NASA Apollo 17 Mission NASA Skylab Orbital Workshop Mission NASA Skylab 2 Mission NASA Skylab 3 Mission NASA Skylab 4 Mission NASA Apollo–Soyuz Test Project Mission NASA STS‑1 Columbia Mission NASA STS‑3 Columbia Mission NASA STS‑7 Challenger Mission NASA STS‑8 Challenger Mission NASA STS‑41B Challenger Mission NASA STS‑41G Discovery (1st female EVA) Mission NASA STS‑51L Challenger (accident) Mission NASA STS‑26 Discovery (Return‑to‑Flight) Mission NASA STS‑31 Discovery (Hubble Launch) Mission NASA STS‑49 Endeavour (first capture EVA) Mission NASA STS‑61 Endeavour (Hubble Servicing 1) Mission NASA STS‑73 Columbia (microgravity) Mission NASA STS‑95 Discovery (John Glenn returns) Mission NASA STS‑107 Columbia (accident) Mission NASA STS‑114 Discovery (RTF‑2) Mission NASA STS‑120 Discovery (Node 2) Mission NASA STS‑125 Atlantis (Final Hubble Service) Mission NASA STS‑132 Atlantis Mission NASA STS‑135 Atlantis (Final Shuttle flight) Mission NASA Artemis I (Orion/ SLS‑1) Mission NASA Artemis II (Planned) Mission NASA Artemis III (Planned lunar landing) Mission NASA Mariner 4 Mission NASA Mariner 6 Mission NASA Mariner 7 Mission NASA Mariner 9 Mission NASA Viking 1 Orbiter/Lander Mission NASA Viking 2 Orbiter/Lander Mission NASA Mars Pathfinder & Sojourner Mission NASA Mars Global Surveyor Mission NASA 2001 Mars Odyssey Mission NASA Mars Exploration Rover – Spirit Mission NASA Mars Exploration Rover – Opportunity Mission NASA Mars Reconnaissance Orbiter Mission NASA Phoenix Mars Lander Mission NASA InSight Mars Lander Mission NASA Mars 2020 (Perseverance & Ingenuity) Mission NASA Mars Sample Return – SRL (planned) Mission NASA Pioneer 10 Mission NASA Pioneer 11 Mission NASA Voyager 1 Mission NASA Voyager 2 Mission NASA Galileo Jupiter Orbiter/Probe Mission NASA Cassini–Huygens Mission NASA New Horizons (Pluto & KBO) Mission NASA Juno Mission NASA Europa Clipper (planned) Mission NASA Parker Solar Probe Mission NASA Solar Orbiter (ESA/NASA) Mission NASA Surveyor 1 Mission NASA Lunar Orbiter 1 Mission NASA Lunar Prospector Mission NASA LCROSS Mission NASA LADEE Mission NASA Lunar Reconnaissance Orbiter (LRO) Mission NASA CAPSTONE Mission NASA VIPER Rover (planned) Mission NASA NEAR Shoemaker Mission NASA Deep Space 1 Mission NASA Stardust Mission NASA Genesis Mission NASA Deep Impact Mission NASA Dawn (Vesta/Ceres) Mission NASA OSIRIS‑REx Mission NASA Lucy Mission NASA DART Mission NASA Landsat‑1 (ERTS‑1) Mission NASA Landsat‑5 Mission NASA Landsat‑9 Mission NASA Terra Mission NASA Aqua Mission NASA Aura Mission NASA Suomi NPP Mission NASA Sentinel‑6 Michael Freilich Mission NASA ICESat‑2 Mission NASA GRACE‑FO Mission NASA SMAP Mission NASA GPM Core Observatory Mission NASA CALIPSO Mission NASA CloudSat Mission NASA NISAR (NASA‑ISRO) Mission NASA Explorer 1 Mission NASA COBE Mission NASA Compton Gamma Ray Observatory Mission NASA Hubble Space Telescope Mission NASA Chandra X‑ray Observatory Mission NASA Spitzer Space Telescope Mission NASA WISE Mission NASA Kepler Mission NASA TESS Mission NASA Fermi Gamma‑ray Space Telescope Mission NASA NICER Mission NASA IXPE Mission NASA Roman Space Telescope (planned) Mission NASA NuSTAR Mission NASA GALEX Mission NASA Swift Mission NASA SOHO (ESA/NASA) Mission NASA Cluster II (ESA/NASA) Mission NASA TIMED Mission NASA STEREO‑A/B Mission NASA MMS Mission NASA IRIS Mission NASA Solar Dynamics Observatory Mission NASA X‑37B OTV‑1 (USAF/NASA liaison) Mission NASA X‑59 QueSST Mission NASA Mars Helicopter Ingenuity Mission NASA Valkyrie R5 Robot Mission NASA Low‑Boom Flight Demo Mission NASA CRS‑1 Dragon Mission NASA CRS‑1 Cygnus Mission NASA Crew Dragon Demo‑2 Mission NASA Starliner OFT‑2 Mission NASA STS-2 (Shuttle flight) Mission NASA STS-4 (Shuttle flight) Mission NASA STS-5 (Shuttle flight) Mission NASA STS-6 (Shuttle flight) Mission NASA STS-41C (Shuttle flight) Mission NASA STS-41D (Shuttle flight) Mission NASA STS-51A (Shuttle flight) Mission NASA STS-61C (Shuttle flight) Mission NASA STS-26 (Shuttle flight) Mission NASA STS-27 (Shuttle flight) Mission NASA STS-29 (Shuttle flight) Mission NASA STS-30 (Shuttle flight) Mission NASA STS-32 (Shuttle flight) Mission NASA STS-34 (Shuttle flight) Mission NASA STS-38 (Shuttle flight) Mission NASA STS-45 (Shuttle flight) Mission NASA STS-60 (Shuttle flight) Mission NASA STS-70 (Shuttle flight) Mission NASA STS-71 (Shuttle flight) Mission NASA STS-73 (Shuttle flight) Mission NASA STS-88 (Shuttle flight) Mission NASA STS-92 (Shuttle flight) Mission NASA STS-97 (Shuttle flight) Mission NASA STS-99 (Shuttle flight) Mission NASA STS-100 (Shuttle flight) Mission NASA STS-104 (Shuttle flight) Mission NASA STS-106 (Shuttle flight) Mission NASA STS-110 (Shuttle flight) Mission NASA STS-112 (Shuttle flight) Mission NASA STS-115 (Shuttle flight) Mission NASA STS-116 (Shuttle flight) Mission NASA STS-117 (Shuttle flight) Mission NASA STS-118 (Shuttle flight) Mission NASA STS-120 (Shuttle flight) Mission NASA STS-122 (Shuttle flight) Mission NASA STS-123 (Shuttle flight) Mission NASA STS-126 (Shuttle flight) Mission NASA STS-130 (Shuttle flight) Mission NASA Vanguard 1 Mission NASA Transit 1B Mission NASA Echo 1 Mission NASA Telstar 1 Mission NASA Syncom 3 Mission NASA ATS‑6 Mission NASA Skynet Mission NASA Nimbus‑1 Mission NASA Nimbus‑7 Mission NASA ERS-1 Mission NASA SeaSat Mission NASA QuikSCAT Mission NASA Jason‑1 Mission NASA Jason‑3 Mission NASA ICESat Mission NASA Earth Observing‑1 Mission NASA Orbiting Carbon Observatory‑2 Mission NASA CYGNSS Mission NASA PACE Mission NASA TRMM Mission NASA Terrestrial Planet Finder (cxl) Mission NASA Laser Interferometer Space Antenna (LISA) Mission NASA Explorer 33 Mission NASA Voyager Interstellar Mission Mission NASA Helios‑A Mission NASA Helios‑B Mission NASA ISEE‑3 (ICE) Mission NASA ACE Mission NASA DSCOVR Mission NASA IBEX Mission NASA Solar Orbiter Heliospheric Imager Mission NASA SAGE‑III ISS Mission NASA SPACE Telescope Imaging Spectrograph Mission NASA ARIEL (ESA/NASA) Mission NASA OSAM‑1 (Restore‑L) Mission NASA Dragonfly (Titan rotorcraft) Mission NASA VERITAS (Venus orbiter) Mission NASA DAVINCI (Venus probe) Mission NASA SPHEREx Mission NASA MAGGIE (Mars Geophysical) Mission NASA CLPS – Peregrine Mission NASA CLPS – VIPER Delivery Mission NASA CAPSTONE Mission NASA Gateway (HALO / PPE) Mission NASA Mars Telecommunication Orbiter (cxl) Mission NASA Mars Polar Lander (MPL) Mission NASA Mars Climate Orbiter Mission NASA Pathfinder Mission Mission NASA SLS Block 1B (Exploration Upper Stage) Mission NASA Orion Crew Module Mission NASA Commercial LEO Destinations – Axiom Station Mission NASA ISS Expedition 1 Mission NASA ISS Expedition 70 Mission NASA CRS‑11 (Dragon) Mission NASA CRS‑21 (Dragon 2) Mission NASA Snoopy CubeSat Mission
Home / IAS Preparation / Origin and Evolution of Earth's Crust!

Unveiling the Geological Journey: Origin and Evolution of Earth's Crust!

Last Updated on Jul 14, 2023
Download As PDF
IMPORTANT LINKS
Agriculture Notes For UPSC Public Administration UPSC Notes Modern History Books For UPSC Overseas Citizen Of India Caste System & Panchayati Raj Godavari River Federalism Indira Point New Development Bank Battle Of Sinhagad Sankalp And Strive Schemes Digital India High Yielding Varieties Economic Growth Development League Of Nations Ease Of Doing Business Mid Day Meal Scheme Wildlife Protection Act 1972 UPSC Notes International Union Conservation Nature

The origin and evolution of Earth's crust started from a hot molten surface that slowly cooled to form igneous rocks. The constant movement of tectonic plates resulted in the continental crust, which is thicker and less dense. Erosion of older rocks and weathering formed sedimentary rocks over time.

This article holds significant value for those aspiring to clear the UPSC IAS exam. Enhance your chances of success by enrolling in UPSC Coaching.

Fig: Layers Of Earth's Crust

The Origin And Evolution Of Earth's Crust

Earth's crust is the outermost, solid part of our planet. The average thickness of the crust is about 25 kilometres. It forms the Earth's surface on which all of life lives and evolves. 

  • When Earth first formed, it was a very hot ball of melted magma. As it cooled over millions of years, the heavier and denser elements sank towards the centre, and the lighter rocks rose to the surface, forming the early crust. This process is known as differentiation. The crust formed first, followed by the mantle and the core.
  • The early crust was probably a global crust made of basic volcanic rocks like basalt and could have a thickness of 50 to 100 kilometres. However, this primitive crust could not withstand the heat from Earth's interior and kept recycling into the mantle.
  • The origin and evolution of Earth's crust continued as our planet cooled further. When Earth's interior reached around half its original temperature, recycling of the crust slowed down. New crust continued to form on the cooling surface from the uprising of magma.
  • Around 4 billion years ago, the modern crust started forming with more varied rock types of granite and sediments in addition to basalt. Granite formed as melted magma rose to the surface and slowly cooled. Sediments accumulate from eroding rocks. This early continental crust was thicker than today's crust at around 50 kilometres.
  • The origin and evolution of Earth's crust witnessed a major change when oxygen started accumulating in the atmosphere around 2.5 billion years ago. This period is called the Great Oxidation Event. With more oxygen in the atmosphere, weathering of rocks became more efficient and produced more sediments. The new sediments binding with the pre-existing crust gave rise to the first protocontinents.
  • The origin and evolution of Earth's crust continued as the protocontinents grew via ongoing sedimentation and magma activity. Crust recycling also became less frequent. About a billion years ago, all the present-day continents started forming and joining together into the supercontinent Rodinia.
  • The origin and evolution of Earth's crust saw several cycles of the assembly and breakup of supercontinents like Rodinia and Pangaea, with the present-day continents shaped as they were now only 250 million years ago. These continent movements were driven mainly by convection currents in Earth's mantle and the rise of the new crust through volcanism.
  • The modern continental crust forming a large part of today's crust is lighter, thicker and composed of rocks like granite and sediments, while the oceanic crust formed at mid-oceanic ridges is denser, thinner and mainly basaltic. The different compositions reflect their different origins and evolutions over time.
  • The origin and evolution of Earth's crust continue even today. New crust is constantly being created at mid-oceanic ridges where hot magma rises to the sea floor and cools. Existing continental and oceanic crust is recycled back into the mantle through subduction at convergent plate boundaries. However, the average thickness and volume of the crust have likely remained more or less the same over the past 500 million years.
  • In summary, the origin and evolution of Earth's crust involved early formation from differentiation of the magma ocean, recycling and reformation with new rock types as Earth cooled, accumulation of sediments, breakup and reassembly of supercontinents, and continuing creation and recycling even today. The present-day distribution of continental and oceanic crust reflects 4 billion years of dynamic changes that have shaped our planet and made life possible on the continents.

FREEMentorship Program by
Ravi Kapoor, Ex-IRS
UPSC Exam-Hacker, Author, Super Mentor, MA
100+ Success Stories
Key Highlights
Achieve your Goal with our mentorship program, offering regular guidance and effective exam strategies.
Cultivate a focused mindset for exam success through our mentorship program.
2 Lakh+ Students Mentored Get
Get Free Mentorship Now
UPSC Beginners Program

Get UPSC Beginners Program SuperCoaching @ just

₹50000

Claim for free
Want to know more about this pass ?
Explore SuperCoaching

The Composition Of Earth's Crust

Fig: Composition Of Earth's Crust

The Earth's crust is the outermost layer of our planet. The origin and evolution of Earth's crust started over 4 billion years ago. The crust is thin and solid but the outer rocky part of a large ball. It is made up of oxygen, silicon, aluminium, iron, magnesium and a few other elements.

  • The Earth's crust is made of rocks and minerals. The rocks contain different minerals formed from chemical elements. Most of the crust is formed of two major types of rocks - igneous rocks and sedimentary rocks.
  • Igneous rocks form when hot magma from the mantle below cools and solidifies. As magma reaches the surface, it forms volcanic lava that hardens to igneous rocks. Over time sedimentary rocks form on top of the igneous rocks from pieces of older rocks and minerals.
  • The average thickness of the crust is around 25 kilometres beneath the oceans and 35 kilometres under the continents. However, the thickness varies in different regions. The continental crust is thicker and less dense compared to the oceanic crust.
  • The oxygen in the crust forms oxides with other elements. Silicon and aluminium form silicates that are the most common minerals. Iron forms various iron oxides and silicates. Calcium forms minerals like calcites and feldspars.
  • The minerals found within the Earth's crust are mainly quartz, feldspar and mica. Most of the crust is comprised of these three common minerals. Other important minerals include amphiboles, pyroxenes, olivines and clays. All these minerals combine to give the Earth's crust its composition.
  • The minerals within igneous rocks tend to be coarser and richer, while those within sedimentary rocks are finer and more altered. Certain trace elements like gold, copper and uranium are found in parts of the crust, which are mined for their practical uses.
  • Over billions of years, the composition of Earth's crust changed due to volcanic activity, earthquakes, erosion and weathering. Carbon dioxide and water released from the interior caused chemical weathering that altered the minerals within the crust.
  • Scientists are still studying the details of the origin and evolution of Earth's crust to better understand the formation and development of our planet of life. The composition and internal structure of the crust reveal a lot about how it has changed over geological time.

Theories Of The Origin Of The Earth’s Crust

Let us look at some of theories of origin and evolution of earth’s crust.

Continental Drift Theory

The continental drift theory proposed by Alfred Wegener suggests that around 200 million years ago, the supercontinent Pangaea broke up into the present-day continents. The continents then drifted apart across Earth's surface, driven by convection currents in the mantle.

According to this theory, the origin and evolution of Earth's crust involved the breakup of Pangaea and the movement of the separating landmasses, changing the configuration of continents over time.

However, continental drift theory could not fully explain how or why the continents move. It lacked evidence for the movement mechanism.

Read More About Continental Drift Theory Here!

Sea Floor Spreading Theory

The seafloor spreading theory proposed by Harry Hess suggested that a new oceanic crust is created at mid-ocean ridges. As the ridges move apart, they carry the adjacent tectonic plates and ocean floor with them. This helps spread the ocean basins.

Plate Tectonic Theory

Plate tectonic theory combines continental drift and seafloor spreading. It proposes that Earth's outer layer consists of rigid plates that move relative to each other. This motion constantly reshapes the surface.

The evolution of Earth's crust according to plate tectonics involved the formation of new oceanic crust at ridges, subduction of oceanic crust at trenches, and collision of continental plates. This leads to the assembly and breakup of supercontinents over time.

Read More About Plate Tectonics Theory Here!

Evidence for Theories

Theories account for features like ophiolites, folded mountains, and differences in continental and oceanic crust compositions, supporting the theories. Theories also predict that as the Atlantic Ocean widens, North America and Europe will continue to move apart.

In summary, these theories together describe how Earth's crust has evolved through processes like supercontinent breakup, new crust formation, and plate collisions. Researchers continue to refine theories with new evidence. 

Conclusion

The origin and evolution of Earth's crust has been a long and complicated process shaping our planet over billions of years. 

Get the Testbook App now!

More Articles for IAS Preparation

Origin And Evolution Of Earth's Crust FAQs

The Earth's crust is made up of rocks and minerals. The main rocks are igneous rocks formed from cooling magma and sedimentary rocks formed from pieces of older rocks. The most common minerals are quartz, feldspar and mica.

The Earth's crust varies in thickness. Under oceans, it is, on average, around 25 kilometres thick and under continents, it is around 35 kilometres thick on average. The continental crust is thicker and less dense.

Scientists believe the Earth's crust first formed around 4.4 billion years ago, It started when the surface of the Earth cooled enough for rocks to solidify from the molten magma.

The Earth's crust has changed slowly over billions of years due to various processes. It includes volcanic activity, erosion, weathering, and plate tectonics. These processes have altered the minerals and rocks that make up the crust.

Studying the composition and structure of the Earth's crust can teach us about how our planet formed and evolved over time. It also provides clues about how and when life first developed on Earth.
Report An Error
Exams Tests Super Practice