Why there are no large impact craters on Earth.

[sjastro]

While the Earth’s atmosphere can play a role through factors such as such as wind and water erosion in erasing the visual evidence of impact craters it is a secondary mechanism.

The size of an impact crater is a function of the kinetic energy KE of the object striking the surface.
The KE is defined by the equation KE = 0.5mv² where m and v are the mass and velocity of the object respectively.

When the object such as an asteroid enters the atmosphere it rapidly decelerates forming a high pressure air front with comparatively little pressure behind or to the sides of the object.
This places the object under considerable stress.
If the pressure build up is considerable, air is forced into the pores and cracks causing the object to fragment with pieces distributing themselves laterally.
This is known as the "pancake effect."
The collection of smaller pieces has a larger front-facing surface area, causing even more stress build up.
In very short order, a runaway fragmentation cascade disintegrates the object, where the loss of KE through deceleration is converted into the KE of individual fragments flying through the atmosphere which may impact the Earth.

The absence of large meteorite craters on Earth compared to what is found on the moon is therefore due to a reduction in the KE through loss of mass and reduction of velocity.
An extreme case occurs where the object explodes above the surface and leaves no crater.
This occurred in 1908 known as the Tunguska event which flattened an estimated 80 million trees over an area of 2,150 km² of forest.

On a less spectacular note a few years ago I observed a bolide which was brighter than the full moon and had a greenish colour probably due to an iron-nickel meteor.
The bolide broke up into a number of fragments each leaving a trail in the sky and was accompanied by a thunderclap sound.

 

[SavedByGrace3]

Impacts tens of millions and even hundreds of millions of years ago have simply been eroded into the earth or covered by natural geologic processes.
The crater that killed the dinosaurs 65 million years ago is still there. It has been eroded and hidden by natural geologic processes. It can easily been detected by special equipment.
APOD: June 4, 1996 - Impact! 65 Million Years Ago (nasa.gov)

 

[Occams Barber]

I was going to post this in the Creation vs Evolution thread which was closed.
While the Earth’s atmosphere can play a role through factors such as such as wind and water erosion in erasing the visual evidence of impact craters it is a secondary mechanism.

The size of an impact crater is a function of the kinetic energy KE of the object striking the surface.
The KE is defined by the equation KE = 0.5mv² where m and v are the mass and velocity of the object respectively.

When the object such as an asteroid enters the atmosphere it rapidly decelerates forming a high pressure air front with comparatively little pressure behind or to the sides of the object.
This places the object under considerable stress.
If the pressure build up is considerable, air is forced into the pores and cracks causing the object to fragment with pieces distributing themselves laterally.
This is known as the "pancake effect."
The collection of smaller pieces has a larger front-facing surface area, causing even more stress build up.
In very short order, a runaway fragmentation cascade disintegrates the object, where the loss of KE through deceleration is converted into the KE of individual fragments flying through the atmosphere which may impact the Earth.

The absence of large meteorite craters on Earth compared to what is found on the moon is therefore due to a reduction in the KE through loss of mass and reduction of velocity.
An extreme case occurs where the object explodes above the surface and leaves no crater.
This occurred in 1908 known as the Tunguska event which flattened an estimated 80 million trees over an area of 2,150 km² of forest.

On a less spectacular note a few years ago I observed a bolide which was brighter than the full moon and had a greenish colour probably due to an iron-nickel meteor.
The bolide broke up into a number of fragments each leaving a trail in the sky and was accompanied by a thunderclap sound.

Hi Sjastro

There's a Creation & Evolution forum available. It's within the Physical & Life Sciences group.
Creation & Evolution

Your OP is interesting - but how does it relate to Creation/Evolution?

OB

 

[dqhall]

Impacts tens of millions and even hundreds of millions of years ago have simply been eroded into the earth or covered by natural geologic processes.
The crater that killed the dinosaurs 65 million years ago is still there. It has been eroded and hidden by natural geologic processes. It can easily been detected by special equipment.
APOD: June 4, 1996 - Impact! 65 Million Years Ago (nasa.gov)
View attachment 319345

Meteor Crater, Arizona
Visitor Info | Meteor Crater | Barringer Space Museum

 

[sjastro]

Hi Sjastro

There's a Creation & Evolution forum available. It's within the Physical & Life Sciences group.
Creation & Evolution

Your OP is interesting - but how does it relate to Creation/Evolution?

OB

It came up in the latter stages of this thread.
It became very nasty.

 

[sjastro]

The oldest impact structure known is the Yarrabubba crater in Australia dated 2,229 ± 5 million years old.

While the crater has eroded away the original radius is determined through magnetic anomalies.
MAGNETIC ANOMALY – Crater Explorer

The presence of shocked zircon and monazite indicating shock metamorphism due to high pressures and temperatures associated with meteorite impacts have also been U-Pb dated to determine when the impact occurred.

Precise radiometric age establishes Yarrabubba, Western Australia, as Earth’s oldest recognised meteorite impact structure | Nature Communications

 

[SavedByGrace3]

It came up in the latter stages of this thread.
It became very nasty.

Sorry about that.

 

[sjastro]

The Henbury craters in Australia which number 13-14 is an example of a larger object which broke up into fragments some of which impacted the surface over a small area.

The site has been dated to ≤4.7 thousand years ago based on the cosmogenic 14C terrestrial age of the meteorite and 4.2±1.9 thousand years ago using fission track dating.
What makes this site interesting the impact may have been witnessed by humans and recorded in the oral traditions of the indigenous people who inhabited the area.

The Henbury crater field lies at the crossroads of several Aboriginal language groups, including Arrernte, Luritja, Pitjantjatjarra, and Yankunytjatjara. It is considered a sacred site to the Arrernte people and would have formed during human habitation of the area.[10] J.M. Mitchell[11] said that older Aboriginal people would not camp within a couple of miles of the Henbury craters. An elder Aboriginal man who accompanied Mitchell to the site explained that Aboriginal people would not drink rainwater that collected in the craters, fearing the "fire-devil" would fill them with a piece of iron. The man claimed his paternal grandfather had seen the fire-devil and that he came from the Sun. An Aboriginal contact said of the crater field: tjintu waru tjinka yapu tjinka kurdaitcha kuka, which roughly translates in the Luritja language as A fiery devil ran down from the Sun and made his home in the Earth. He will burn and eat any bad blackfellows. This indicates a living memory of the event.[12]

 

[AV1611VET]

On a less spectacular note a few years ago I observed a bolide which was brighter than the full moon and had a greenish colour probably due to an iron-nickel meteor.

The IAU has no official definition of "bolide",

SOURCE

Oh-Oh!

 

[Halbhh]

... a few years ago I observed a bolide which was brighter than the full moon and had a greenish colour probably due to an iron-nickel meteor.
The bolide broke up into a number of fragments each leaving a trail in the sky and was accompanied by a thunderclap sound.

Sweet! I've seen a few bright meteors, but not close enough for sound, and not greenish. I bet that was fun.

 

[Petros2015]

a) i'm pretty sure there are
b) i'd expect 70% of the impacts the have landed in the water
c) sometimes goats fall in the craters and fill them up

 

[Astrophile]

I was going to post this in the Creation vs Evolution thread which was closed.
While the Earth’s atmosphere can play a role through factors such as such as wind and water erosion in erasing the visual evidence of impact craters it is a secondary mechanism.

The size of an impact crater is a function of the kinetic energy KE of the object striking the surface.
The KE is defined by the equation KE = 0.5mv² where m and v are the mass and velocity of the object respectively.

When the object such as an asteroid enters the atmosphere it rapidly decelerates forming a high pressure air front with comparatively little pressure behind or to the sides of the object.
This places the object under considerable stress.
If the pressure build up is considerable, air is forced into the pores and cracks causing the object to fragment with pieces distributing themselves laterally.
This is known as the "pancake effect."
The collection of smaller pieces has a larger front-facing surface area, causing even more stress build up.
In very short order, a runaway fragmentation cascade disintegrates the object, where the loss of KE through deceleration is converted into the KE of individual fragments flying through the atmosphere which may impact the Earth.

The absence of large meteorite craters on Earth compared to what is found on the moon is therefore due to a reduction in the KE through loss of mass and reduction of velocity.
An extreme case occurs where the object explodes above the surface and leaves no crater.
This occurred in 1908 known as the Tunguska event which flattened an estimated 80 million trees over an area of 2,150 km² of forest.

On a less spectacular note a few years ago I observed a bolide which was brighter than the full moon and had a greenish colour probably due to an iron-nickel meteor.
The bolide broke up into a number of fragments each leaving a trail in the sky and was accompanied by a thunderclap sound.

I was going to post this in the Creation vs Evolution thread which was closed.
While the Earth’s atmosphere can play a role through factors such as such as wind and water erosion in erasing the visual evidence of impact craters it is a secondary mechanism.

The size of an impact crater is a function of the kinetic energy KE of the object striking the surface.
The KE is defined by the equation KE = 0.5mv² where m and v are the mass and velocity of the object respectively.

When the object such as an asteroid enters the atmosphere it rapidly decelerates forming a high pressure air front with comparatively little pressure behind or to the sides of the object.
This places the object under considerable stress.
If the pressure build up is considerable, air is forced into the pores and cracks causing the object to fragment with pieces distributing themselves laterally.
This is known as the "pancake effect."
The collection of smaller pieces has a larger front-facing surface area, causing even more stress build up.
In very short order, a runaway fragmentation cascade disintegrates the object, where the loss of KE through deceleration is converted into the KE of individual fragments flying through the atmosphere which may impact the Earth.

The absence of large meteorite craters on Earth compared to what is found on the moon is therefore due to a reduction in the KE through loss of mass and reduction of velocity.
An extreme case occurs where the object explodes above the surface and leaves no crater.
This occurred in 1908 known as the Tunguska event which flattened an estimated 80 million trees over an area of 2,150 km² of forest.

On a less spectacular note a few years ago I observed a bolide which was brighter than the full moon and had a greenish colour probably due to an iron-nickel meteor.
The bolide broke up into a number of fragments each leaving a trail in the sky and was accompanied by a thunderclap sound.

The Earth does have large impact structures. The Vredefort Ring in South Africa has d = 160-300 km and was produced by the impact of an asteroid 10-15 km in diameter; Sudbury (Canada) has d = 130 km, Chicxulub (Mexico) has d = 180 km, and Manicouagan (Canada), Popigai (Siberia) and Lake Acraman (Australia) have d = 90-100 km, and were produced by asteroids 5-8 km in diameter. I doubt whether the Earth's atmosphere had much effect on the kinetic energy of these asteroids.

A more probable explanation for the absence of giant impact structures on Earth may be that the largest lunar craters, including the mare basins, were formed more than 3.8 billion years ago (during or before the Late Heavy Bombardment), and no terrestrial rocks of that age have been preserved.

 

[Astrid]

Most of "earth" is water.

For ones that make a hole...
There's erosion.
Deposition.

There's a huge Crater in NE Iowa, USA.
Who knew that?
All you can see is cornfield.
Has, ftm, has anyone seen the American
mid continental rift?
Mars and the moon don't do tectonics at all,
and next to no erosion.

 

[sjastro]

The Earth does have large impact structures. The Vredefort Ring in South Africa has d = 160-300 km and was produced by the impact of an asteroid 10-15 km in diameter; Sudbury (Canada) has d = 130 km, Chicxulub (Mexico) has d = 180 km, and Manicouagan (Canada), Popigai (Siberia) and Lake Acraman (Australia) have d = 90-100 km, and were produced by asteroids 5-8 km in diameter. I doubt whether the Earth's atmosphere had much effect on the kinetic energy of these asteroids.

A more probable explanation for the absence of giant impact structures on Earth may be that the largest lunar craters, including the mare basins, were formed more than 3.8 billion years ago (during or before the Late Heavy Bombardment), and no terrestrial rocks of that age have been preserved.

The craters you are describing were initially classified as “possible impact structures” which have subsequently been identified as craters.
The craters on Earth I had in mind are those with well defined structures resembling lunar craters such as the Meteor crater, Wolf Creek, Henbury etc.
These craters are considerably smaller than their counterparts on the Moon formed well after the Late Bombardment period such as Copernicus.

Scientists can tell the direction of the impacting body forming the craters as the atmosphere causes the body to break up before impact into fragments as described in the OP which forms a strewn field.

Example of meteorite strewn field: distribution ellipse of Pultusk meteorite​

It’s estimated 25 million meteors per day enter the Earth’s atmosphere of various sizes ranging from dust size up to the size of buses.
The vast percentage burn up due to their small size, larger meteors or bolides (fireballs) may break up or explode in the atmosphere into smaller fragments some of which may reach the Earth as meteorites.

As can be seen atmospheric explosions are quite frequent and the Chelyabinsk explosion which resulted in meteorites was equivalent to a 440 kiloton explosion (by comparison Hiroshima and Nagasaki were 15 and 20 kilotons respectively).

If it wasn’t for our atmosphere these explosions would turn into impact events and devastate the Earth.

 

[Astrophile]

The craters you are describing were initially classified as “possible impact structures” which have subsequently been identified as craters.
The craters on Earth I had in mind are those with well defined structures resembling lunar craters such as the Meteor crater, Wolf Creek, Henbury etc.
These craters are considerably smaller than their counterparts on the Moon formed well after the Late Bombardment period such as Copernicus.

Scientists can tell the direction of the impacting body forming the craters as the atmosphere causes the body to break up before impact into fragments as described in the OP which forms a strewn field.

Example of meteorite strewn field: distribution ellipse of Pultusk meteorite​

It’s estimated 25 million meteors per day enter the Earth’s atmosphere of various sizes ranging from dust size up to the size of buses.
The vast percentage burn up due to their small size, larger meteors or bolides (fireballs) may break up or explode in the atmosphere into smaller fragments some of which may reach the Earth as meteorites.

As can be seen atmospheric explosions are quite frequent and the Chelyabinsk explosion which resulted in meteorites was equivalent to a 440 kiloton explosion (by comparison Hiroshima and Nagasaki were 15 and 20 kilotons respectively).

If it wasn’t for our atmosphere these explosions would turn into impact events and devastate the Earth.

You are right up to a point. Craters such as Meteor Crater, Wolf Creek, Henbury, Odessa, etc., are much smaller than comparatively young lunar craters such as Copernicus, Tycho, Kepler and Aristarchus, and they were formed by meteorites that broke up, at least partially, before they hit the ground. Also, as you say, many large bolides explode in the atmosphere rather than reaching the ground, where they might have formed craters. However, these craters would have been at most hundreds of metres in diameter, comparable to Meteor Crater, Henbury or Wolf Creek rather than to Copernicus.

However, these terrestrial craters are also much younger than the comparatively young lunar craters; they are of Pleistocene age (< 2 million years), whereas Copernicus is about 800 million years old, Tycho is about 108 million years old, and Aristarchus is about 450 million years old.

The large terrestrial impact structures that I mentioned in my previous post were all formed after the Late Heavy Bombardment. Chicxulub is both larger and younger than either Tycho or Copernicus; Popigai is about the same size as Tycho and Copernicus and is also younger than either. Manicouagan and Acraman are also younger than Copernicus and about the same size.

 

[sjastro]

a) i'm pretty sure there are
b) i'd expect 70% of the impacts the have landed in the water
c) sometimes goats fall in the craters and fill them up

Compared to what?
The largest impact events found on Earth are puny compared to other craters found in the solar system.
List of largest craters in the Solar System - Wikipedia

 

[Astrid]

Compared to what?
The largest impact events found on Earth are puny compared to other craters found in the solar system.
List of largest craters in the Solar System - Wikipedia

Some say the moon was formed by an impact
event

 

[sjastro]

You are right up to a point. Craters such as Meteor Crater, Wolf Creek, Henbury, Odessa, etc., are much smaller than comparatively young lunar craters such as Copernicus, Tycho, Kepler and Aristarchus, and they were formed by meteorites that broke up, at least partially, before they hit the ground. Also, as you say, many large bolides explode in the atmosphere rather than reaching the ground, where they might have formed craters. However, these craters would have been at most hundreds of metres in diameter, comparable to Meteor Crater, Henbury or Wolf Creek rather than to Copernicus.

However, these terrestrial craters are also much younger than the comparatively young lunar craters; they are of Pleistocene age (< 2 million years), whereas Copernicus is about 800 million years old, Tycho is about 108 million years old, and Aristarchus is about 450 million years old.

The large terrestrial impact structures that I mentioned in my previous post were all formed after the Late Heavy Bombardment. Chicxulub is both larger and younger than either Tycho or Copernicus; Popigai is about the same size as Tycho and Copernicus and is also younger than either. Manicouagan and Acraman are also younger than Copernicus and about the same size.

As I mentioned in my previous post the scope for comparison being made was between well defined craters found on the Moon and Earth which I suspect was the same standard used by the character in the other thread you were debating.

The facts are all we have available on Earth are relatively small craters produced by a limited KE on impact due to mass loss in the atmosphere prior to impact.

The impact events you have mentioned such as Chicxulub, Popigai, Manicouagan and Acraman were caused by massively large asteroids 5 -20 km in diameter and given their very high inertia are not going to be slowed downed by the Earth’s atmosphere and would not explode or fragment like the much smaller asteroids or meteoroids.
The initial crater formation was also probably larger than what can be discerned today.

 

[sjastro]

Some say the moon was formed by an impact
event

This is the giant impact hypothesis.

 

[Petros2015]

Compared to what?
The largest impact events found on Earth are puny compared to other craters found in the solar system.

Consider the ratio between the size of the goats found on earth compared to the size of other goats found in the solar system.

In some slightly more seriousness, I have heard our moon is pretty unique in terms of size and orbit, and functions a lot like a shield. Asking why we have no large impact craters is a bit like asking why we have no holes in us while our bodyguard has dozens.

Probably the real answer has more to do with this though:
Why Does the Moon Have Craters? | NASA Space Place – NASA Science for Kids
See? Goats. No goats on the moon.

Be patient, I'm sure we'll get one eventually.