The Complete Last Day on Earth: Survival Wiki Guide

Welcome to the Last Day on Earth: Survival Wiki Guide. On this page, you'll find a collection of useful tips, tricks, and information to help you thrive in the world of LDoE.

Last Day on Earth: Survival is a zombie survival game developed by Kefir! Studios for Android and iOS. Although still in beta, the game has already shown great potential and continues to be one of the most popular survival games on the Google Play Store.

Table of Content

If you've played PC titles like H1Z1 or DayZ, you'll find some familiar elements here. You take on the role of a lone survivor in a post-apocalyptic world overrun by zombies—and sometimes, other hostile players—in a multiplayer setting.

The game begins with your character stranded in a desolate area infested with zombies. This spot will become your base, your safe zone, and the starting point of your survival journey.

In Last Day on Earth, you can craft items, build and upgrade your shelter, fight off zombies and other survivors, and gather vital resources to keep yourself alive as long as possible.

Explanation of the Main Menu in Last Day on Earth

Before diving deeper into the game, it’s a good idea—especially for beginners—to understand the main menu options first.

Build House

This menu allows you to move furniture, build new structures, and upgrade your house. To upgrade, simply tap this menu, then select the floor, wall, or door you want to enhance.

Inventory

Here you can view all the items your character is carrying or wearing. You can increase your inventory space by equipping a backpack.

Blueprints

This is where you craft essential items for survival. You can also see the required materials for crafting.

Each time your character levels up, you earn 2 points that can be used to unlock new craftable items. So the higher your level, the more tools and gear you can make.

Shop

In this menu, you can purchase items using real money. You can also access your in-game inbox here.

Ambush

This feature lets you ambush other players from a distance using a Dragunov Rifle. It’s a long-range attack option.

Build New Base

You can set up a second home in a different area. But first, you’ll need to build a Zombie Truck to transport supplies.

Clans

This is where you can join or create a Clan. To create one, you’ll need to build a Radio Tower first.

Joining a Clan comes with several benefits, such as:

• Access to special zones like Pump Jacks and Oil Refineries, which contain valuable resources like stone, metal, and fuel.
• Having your own Clan Headquarters.

For a more detailed guide, check out: How to Build a Radio Tower and Join a Clan in Last Day on Earth: Survival.

Settings

Here you can change the language, sound, and graphics, and disconnect your Google Play account if you want to repeat from the beginning

List of Locations You Can Visit in Last Day on Earth

There are various locations you can explore in Last Day on Earth. However, some of them require specific vehicles, like the ATV or Helicopter to access.

To travel to another location, you must first walk to a green grassy area near your base. From there, the world map will appear, showing all available destinations.

Traveling between locations takes a certain amount of real-time minutes, depending on the distance. You can speed this up by using Energy or a Chopper.

Other Survivors’ Bases

You can raid other players' bases to steal their items. However, you’ll need the right tools to break in, depending on the wall material:

• Pine Logs (Wood walls): Use a Hatchet
• Pine Planks (Upgraded wood): Use an Iron Hatchet
• Stone Bricks (High-level walls): Use C-4

Farming Areas

These are resource-rich areas where you can gather materials, level up your character, and collect loot to upgrade your base. Each area has a danger level indicated by color:

• Green Zones — Low Danger (Safe for beginners)
  Enemies: Roaming Zombies (common), Fast Biters (rare), Gray Wolves, Floater Bloaters (rare), and sometimes other Survivors.
• Yellow Zones — Medium Danger (Stay alert)
  Enemies: Fast Biters (main threat), Roaming Zombies, Toxic Spitters, Wolves, Floater Bloaters, occasional "The Big One", and hostile Survivors.
• Red Zones — High Danger (Only for well-equipped players)
  Enemies: Almost all types of zombies, including stronger variants. Be wary of ambushes from other survivors.

Some of the locations categorized as farming areas are:

1. Limestone Ridge

Threat: 1 (Green zone)
Stone: 1
Wood: 1
Metal: 1
Loot: 1

2. Limestone Cliffs

Threat: 2 (Yellow zone)
Wood: 1
Stone: 2
Metals: 2
Loot: 2

3. Limestone Spires

Threats: 3 (Red zone)
Wood: 1
Stone: 3
Metals: 3
Loot: 3

4. Pine Bushes

Threats: 1 (Green zone)
Wood: 1
Stone: 3
Metals: 1
Loot: 3

5. Pine Grove

Threats: 2 (Yellow zone)
Wood: 2
Stone: 1
Metals: 1
Loot: 2

6. Pine Wood

Threats: 3 (Red zone)
Wood (Pine and Oak): 3
Stone: 1
Metals: 0
Loot: 3

7. Oak Bushes

Threats: 1 (Green zone)
Oakwood: 1
Stone: 3
Metals: 1
Loot: 3

8. Oak Grove

Threats: 2 (Yellow zone)
Oakwood: 2
Stone: 1
Metals: 1
Loot: 2

9. Oak Wood

Threats: 3 (Red zone)
Oakwood: 3
Stone: 1
Metals: 0
Loot: 3

Oak Bushes, Grove, and Wood are only accessible if you have an ATV.

10. Infected Forest

Although included in the red zone, this location is very different from the others. Never come here without full equipment if you do not want to die. Here is the home of The Big One.

Threats: 3
Wood: 3
Stone: 1
Metals: 0
Loot: 3

11. Wooded Foothills

12. Frosty Backwoods

The numbers like 0, 1, 2, and 3 below the word "threat" are indicators of the amount of material/stuff available in that location. The higher number means more stuff you can get.

Military Bunker (Alfa to Zulu)

Once an army base, the Military Bunker has now become a stronghold for zombies. The outer area is safe — there are no zombies outside, only a few trees you can cut down for wood.

Inside the bunker, items you collect will not respawn, so loot wisely. There is a locker in the main building that you can use as temporary storage for your gear and supplies.

To access the main building of the bunker, you’ll need a CAC Card that matches the bunker you want to enter. Each card unlocks a different section of the Military Bunker complex.

Here are the known CAC Cards currently available in the game:

• CAC Card A (Alfa) – Found in yellow zones or sometimes at other survivors’ bases.
• CAC Card B (Bravo) – Found in loot boxes in yellow zones.
• CAC Card C (Charlie) – Found in the Bravo Bunker locker
• CAC Card D (Delta) – [Currently no info provided]
• CAC Card F (Foxtrot) – [Currently no info provided]
• CAC Card R (Romeo) – Can be obtained from the Plane Crash event.
• CAC Card Z (Zulu) – Dropped by The Big One after defeating it.

Each bunker may have unique challenges and rewards, so prepare accordingly. These bunkers are key to advancing your gear and uncovering more of the game’s story.

Bunker Alfa

When you first arrive at Bunker Alfa, you’ll see a green zone and a soldier's corpse lying in front of the main entrance. Originally, this body provided CAC Card A, which is required to open the main bunker door — but as of now, this is no longer the case.

Bunker Alfa contains a multi-level basement (floors 1 to 6), accessible through the Vault Door. Inside, you'll face dangerous traps and powerful zombies guarding the area.

By defeating zombies in the bunker, you can collect green, yellow, and red coupons. These coupons can be exchanged for crates filled with valuable loot — including weapons and rare crafting materials for vehicles such as the Chopper, ATV, and even the Helicopter. The items you get depend on your luck.

To unlock the Vault Door and access the basement, you’ll need the Vault Code, which changes every two days. When the code resets, all enemies inside the bunker also respawn.

You can obtain the current Vault Code from:

• Your CB Radio at home
• Army corpses marked with a red X found randomly in farming zones

Bunker Alfa Code Today

If you’ve already traveled to Bunker Alfa but forgot to check the code on your CB Radio, you could previously find the daily updated code here on this site.

Note: We are no longer updating the Bunker Alfa Vault Code.

Bunker Bravo

The exterior of Bunker Bravo resembles Bunker Alfa, but with a noticeably drier and more desolate atmosphere. To access the main building, you’ll need CAC Card B.

Unlike Bunker Alfa, CAC Card B must be found in the wild — typically from loot boxes in yellow or red zones, or occasionally from AirDrop Supply events.

Be cautious when entering Bunker Bravo. Upon unlocking the main door, you’ll immediately face a group of zombies, including:

• 15 Fast Biters
• 1 Floater Bloater
• 1 Toxic Abomination

As of now, the basement of Bunker Bravo is inaccessible due to a broken machine that prevents the Vault Door from being opened.

Recommended Minimum Supplies:

• Weapons: 1 Glock 17 and 1 Machete (for safe play), or 2 full durability Machetes
• Armor: Full Tactical Armor (ideal), though lower-tier armor can work if you're cautious
• Food: At least 20 Carrot Stews, plus some extra food or healing items
• Drink: A few Bottles of Water

Bunker Charlie

Bunker Charlie is located on a remote island in the middle of the sea. To reach it, you must first acquire and use a Helicopter.

Access to the bunker requires CAC Card C, which can be found inside one of the lockers in Bunker Bravo.

Important Note: Do not attempt to enter Bunkers Alfa, Bravo, or Charlie without proper preparation. This includes a solid strategy, sufficient weapons, armor, healing items, food, and drink. Going in unprepared can result in losing valuable resources or even death.

Pump Jack

Here you can get Limestone, Gasoline, and Metals. However, you must join a Clan first to access this place.

Watch Tower

The Watch Tower is a new location introduced in update 1.6.0. Unlike before, you can now access this area without needing an ATV.

Visiting the Watch Tower allows you to unlock secret zones that were previously hidden on the map — but getting in won’t be easy.

Upon arrival, you’ll need a Crowbar to open the locked door marked “Keep Out.” Inside, you’ll face tough enemies like Floater Bloaters and Toxic Abominations, so be prepared for a fight.

To fully activate the Watch Tower, you must bring a finalized Electric Generator. You can craft this from the Blueprints menu at your base. A Chopper is also required to transport the generator from your base to the tower.

Tip: Before heading to this location, make sure to bring the following:

• A Crowbar
• A finalized Electric Generator
• Some firearms or strong melee weapons

After placing the generator in the tower, a wave of zombies will attack — drawn by the noise. Be ready to defend yourself.

Once activated, the Watch Tower will permanently unlock a new zone on the map, including areas with the Winter biome.

Additionally, you’ll find Oak Trees in this area. You can chop them down to collect Oak Logs, but you’ll need an Iron Hatchet to do so.

Last Day on Earth: Survival Events

At random times, special events may appear in Last Day on Earth: Survival. These events are marked on the world map with a blue exclamation mark (!).

Some of these events offer huge rewards, so don’t miss them when they show up — they’re time-limited and may disappear quickly.

Here are some of the key events you should watch for:

Humanitarian Airdrop Supply

Military soldiers drop supply crates containing valuable items like weapons, crafting materials, and sometimes vehicle parts.

The area is guarded by many zombies that often respawn suddenly. Be sure to bring weapons and healing supplies before heading to this event.

Plane Crash

A plane crash is a blessing in disguise. You can loot tons of valuable items — including weapons, full armor, and crafting materials — scattered around the crash site.

This event is less dangerous than the Airdrop Supply. You’ll mostly encounter Roaming Zombies and Gray Wolves. So if you're low on gear, it's still safe to go — you don’t need to bring much, or anything at all.

Note: This event rarely appears once you reach level 35 or higher.

Zombie Horde

Every 24 hours, a horde of zombies marches toward your home base. If you’re at home when this happens, you’ll see them trying to break through your walls.

If your base is still made of Pine Logs and lacks traps or reinforcements, the horde can easily destroy your walls.

To avoid this, you can simply stay offline or leave your base during the attack. The horde will only destroy one wall and then disappear.

Update 1.5.6: The horde can now destroy multiple (five or more) Pine Log walls, even if you’re offline — so reinforcing your base is more important than ever.

Dealer

The Dealer event unlocks after you build a CB Radio. He’ll offer trades where you exchange specific items he asks for in return for a Weapon Crate — which contains random weapons.

The Dealer’s requests are randomized and can range from easy to hard, depending on what he wants.

You can attack the Dealer if you want, but beware — he’ll retaliate with an M16. So yeah… don’t try anything funny 😅.

Healer

The Healer appears at your base near the broken truck once a day after the Zombie Horde attack. He offers you a choice of special foods, each with a unique temporary bonus. After choosing one, you must watch an ad to activate the effect.

Here’s what each food does:

• Brainweed Seeds: Doubles the EXP gained (+100% EXP boost).
• Herbal Mix: Increases unarmed (fist) attack damage by 30%.
• Infected Venison: Boosts melee weapon damage by 20%.
• Muddy Broth: Increases your chance of finding vehicle parts by 5%.
• Muscle Vines: Instantly restores your energy to 100 (no duration).
• Strange Berries: Increases your chance of finding weapons by 5%.
• Other Foods: Additional effects may be added in future updates.

Note: All effects last for 1 hour, except for Muscle Vines, which provides an instant effect only.

💡 Tips and Tricks

If you have enough coupons to exchange at Bunker Alfa for crates containing weapons, armor, or vehicle parts, don’t redeem them right away!

Instead, eat Muddy Broth first to activate the 5% increased chance of finding rare parts like the gas tank or motorcycle handlebars. That small boost can make a big difference, especially since these parts are so hard to come by.

Likewise, if you're aiming to collect more guns, eat Strange Berries before opening weapon crates to improve your chances.

Rest Stop Event

This event was introduced in update 1.5.8. To access it, you must have a Chopper. Like the Plane Crash event, the Rest Stop offers valuable loot — but it’s much more dangerous.

There are four possible scenarios when entering this area:

1. Ambush Setup: You’ll meet a friendly-looking Survivor (NPC) who tries to lead you to his “friends.” But it’s a trap — once you arrive, they’ll ambush and attack you.

2. Survivor in Trouble: A Survivor will ask for help because his friend is surrounded by zombies. These Survivors won’t attack unless you hit them or try to loot their items.

3. Territorial Hunters: Three Survivors will be present — two by their Choppers and one hunting deer. They’ll demand that you leave the area or they’ll become hostile. They don’t want anyone else hunting there.

4. Gang Fight: Two rival groups (8 Survivors total) are fighting over loot. If you stay out of it, they’ll start attacking each other. You can then pick off the weakened survivors and loot the area. This is the best version of the Rest Stop event for easy gear and resources.

No matter which scenario you face, your best option is to fight and loot. If you defeat them, you can take everything — including their weapons, armor, and anything stored on their bikes.

Pro Tip: Always come prepared with weapons, healing items, and food before entering this event. It can turn deadly fast!

Wrecked Ship

Smuggler's Camp

How to Trigger Rest Stop, Humanitarian Airdrop, Plane Crash, and Dealer Events

These special events often appear when your energy is low (around 30 or less) or when you're frequently entering and exiting different zones.

Follow these steps to increase your chances of triggering them:

1. Start from your base and select the farthest map location. Make sure you have at least 100 energy and use it to speed up the journey.
2. Farm the area to make the trip worthwhile and further reduce your energy. Once done, exit the area. A special event may appear right away.
3. If no event appears, return to your base using energy again to speed up travel.
4. Drop off collected items to free up your inventory.
5. Exit your home base. At this point, one of the following events often appears: Rest Stop, Humanitarian Airdrop, Plane Crash, or Dealer.

Tip: Low on energy? Watch ads to earn more. Tap a location, choose “Use Energy,” watch a short video, and receive +15 energy.

Last Day on Earth Survival Guide

The key to this game is survival—every second matters. If you waste time or make the wrong move, you could die for nothing.

When you die, everything in your backpack is lost forever—unless you die in specific areas like your Base, the Military Bunker, or during time-limited events such as Humanitarian Airdrops or the Crashed Plane.

If you die in these areas, there’s still a chance to retrieve your loot from your corpse. But for events, make sure you get back there before the event disappears, or everything will be lost.

There are many ways to die: starvation, dehydration, toxic gas (only found in Bunkers), cold, or being killed by Zombies or other Survivors.

When your character is starting to get hungry or thirsty, a message like “I’m hungry” or “I’m thirsty” will appear, along with an icon above their head. Once either Hunger or Thirst hits 0, you’ll begin to lose Health Points (HP) and eventually die.

Keep in mind—Hunger and Thirst decrease rapidly, so always stay stocked up on food and water.

How to Get Food

Food in LDoE comes in two main types: raw and cooked. The difference lies in how much they restore your HP and hunger/thirst bars.

Raw food gives only a small amount of recovery, while cooked food offers significantly more. So whenever possible, cook your food before eating. But in emergencies, eating it raw is better than nothing.

Here’s a list of some food items you can find in Last Day on Earth and how to get them:

1. Berry

Berries can be obtained easily from the Farming Area. The map will show a picture of the plant.

HP: 5
Hunger: 2
Thirst: 1

2. Berry Tea

You must create a Campfire first to make this. To create Campfire it takes 5 Pine logs, 5 Limestone, and 1 Plant Fiber.

Just put 3 berries at the Campfire and fill the fuel with wood, a few minutes later Berry Tea will be ready to drink.

HP: 0
Hunger: 5
Thirst: 30

3. Carrot

You have to make a Garden Bed to get carrots. Materials needed are 5 Pine Log and 1 Plant Fiber to make a Garden Bed.

As for the Carrot seeds, can be obtained when you take Plant Fiber in the Farming Area.

HP: 15
Hunger: 25
Thirst: 5

4. Carrot Stew

Cook Carrots through the Campfire.

HP: 20
Hunger: 25
Thirst: 5

5. Raw Meat

Raw meat is obtained from animal hunting (deer) or wolves in the Farming Area. To kill a deer, you have to sneak by clicking on the icon located in the bottom right corner of the screen, then after the close, just attack him.

HP: 7
Hunger: 5
Thirst: 5

6. Juicy Steak

Cook raw through Campfire.

HP: 20
Hunger: 30
Thirst: 5

7. Jerky

You just have to put the Raw Meat on the Meat Dryer to make it. It takes 5 Pine Plank, 12 Rope, and 10 Limestone to make a Meat Dryer.

HP: 20
Hunger: 40
Thirst: 5

8. Baked Bean

You can get it from Loot Box in the Farming Area.

HP: 15
Hungry: 25
Thirst: 5

Tips: Make in consecutive 2 Garden Bed, 2 Campfire, and 2 Meat Dryer, if you can make it already. I am sure you will avoid starving to death.

Read also: The Most Efficient Fuel in Last Day on Earth: Survival

How to Get Water

Water is essential for survival, and luckily, it’s easy to get if you build a Rain Catcher. To craft one, you’ll need:

• 10 Pine Logs
• 3 Pieces of Cloth
• 2 Scrap Metal

Even though it never actually rains in the game, the Rain Catcher will still produce water. Just place an empty bottle inside it, and after a few minutes, it will be filled with drinkable water (Restores 50 Thirst).

Other Ways to Get Water

If you don’t have any empty bottles yet, you can find bottled water in:

• Loot crates and bags
• Farming Airdrop Supplies
• Crashed Planes
• Military Bunkers
• Enemy Survivor bases

Alternative Drinks

You can also drink Beer and Berry Tea to temporarily relieve thirst. But be warned—if you drink Beer, your character will immediately need to pee (yes, seriously!).

Tips:

• Never throw away empty bottles—reuse them with the Rain Catcher.
• Build at least two Rain Catchers to ensure a steady supply of water.

How to Beat Zombies and Other Survivors

Defeating enemies is fairly easy if you have strong weapons, good armor, and enough food. Even without much strategy, you can often survive. But what if you're low on equipment—or don’t have any at all?

In that case, you'll need some strategy and technique to stay alive. Here are some tips that can help:

1. Use the Sneak Attack Technique

Tap the sneak icon in the bottom right corner to enter stealth mode. Sneaking lets you quietly approach zombies and land a powerful first hit—dealing 3× more damage than a normal attack.

This is especially useful for eliminating enemies one by one without drawing attention.

2. Lure Zombies One at a Time

If there are groups of zombies close together, sneak attacks may not be an option. Instead, try to lure them individually by walking nearby or using ranged weapons like a bow.

Once one zombie notices you, it will follow you while the others stay in place. Fighting them one at a time makes it much easier to survive.

3. Leave the Area If You’re Surrounded

If you’re being chased by too many zombies—or a combination of zombies and hostile Survivors—don’t hesitate to leave the area. You can always return later.

When you re-enter, most zombies will return to their original positions, and any hostile Survivor chasing you will likely disappear.

However, if you're confident in your ability to fight, it's worth the risk—some Survivors carry valuable loot.

Note: Certain zombies have special abilities and require unique tactics to defeat.

Farming Guide

Farming materials are an essential part of surviving in Last Day on Earth: Survival. It also helps you level up faster. That’s why it’s important to farm efficiently. Here's the step-by-step farming method I often use:

1. Choose the Right Farming Location

I recommend farming only in green or yellow zones—avoid red zones unless necessary. If you're farming basic materials like logs, limestone, or iron ore, go to green zones.

If your goal is both farming and leveling up, go to yellow zones. However, some resources like oak logs are only available in red zones, so you’ll have to go there eventually.

Here are examples of where to farm specific materials:

• Wood (Pine Logs) → Pine Bushes or Pine Grove
• Limestone & Iron Ore → Limestone Ridge or Limestone Cliffs
• Oak Logs → Oak Bushes, Oak Grove, and Red Zones

2. Prepare Your Gear Before Leaving Home

Here’s the minimum equipment you should bring:

• Farming Tools: Hatchet or Pickaxe (depending on the material you want)
• Weapons:
  • Green Zone → Spear or basic melee weapon
  • Yellow Zone → Melee weapon with 20+ damage
  • Red Zone → Firearms (for better survival)
• Armor: Shirt, Cargo Pants, Dad Hat, and Sneakers (optional for green zones)
• Food: Bring up to 20 of one kind: Carrot Stew, Juicy Steak, or Jerky
• Drinks: Bottle of Water or Berry Tea

Important: Leave your valuable items at home to avoid losing them.

3. Clear All Zombies and Enemy Survivors

Once you arrive at your chosen location, eliminate the zombies and any enemy survivors first. You can follow the strategies I've mentioned earlier in this guide.

4. Use the "Auto" Feature to Farm

After clearing the area, tap the "Auto" button at the bottom-left of the screen to start farming automatically. Your character will collect all available resources for you.

If your inventory becomes full, don’t hesitate to discard unimportant items. You can also use loot boxes found in the area to temporarily store items.

5. Double-Check the Map

Make sure you’ve collected all resources. Open the map in the top-right corner. If you still see tree, rock, or plant icons, yellow dots, or "X" marks, it means there are items left to collect.

Once you're done, return to your home base, store or use your items, and repeat steps 1–5.

Other Tips and Tricks

• Don’t waste food or medicine when you're about to level up—your Health Points (HP) will be fully restored automatically.
• Upgrade your house to better withstand zombie attacks and prevent your items from being stolen by other survivors.
• If you want to craft a Chopper, you must first upgrade your floor to level 2. The Chopper blueprint can only be placed on level 2 floors.
• Place important items or food in your pocket slot for quick access during battles or emergencies.
• To view an item description, press and hold the item in your inventory—a short explanation will pop up.
• If you're hit by a Toxic Spitter and get covered in vomit, take a shower to remove the smell—otherwise, your body odor can attract zombies.
• When chopping trees, mining rocks, or fighting 1-on-1, just hold the action button—there’s no need to tap it repeatedly.

FAQs

Q: I want to play this game. How do I download it?

A: You can download it from the Play Store or App Store:
Android: goo.gl/JQu42X
iOS: goo.gl/wnUkgA

Q: I'm a beginner. What should I do first?

A: Start by gathering basic resources, leveling up your character, and crafting essential items like the Catcher, Garden Bed, and Campfire. Then, build your first house for protection.

Q: Will all progress be reset after the beta ends?

A: It’s unclear for now. There's a possibility that some progress, especially your level, might be reset after the official release. So don't play too intensely if you're worried about a reset. However, gaining experience now can still be very useful later.

Q: How do I change my name?

A: Click here to learn how. (can't change now)

Q: If I steal from other survivors’ houses, can my stuff be stolen too?

A: At the moment, no one can steal from you. However, there is now a raid system in the game, so stay alert.

Q: Are the characters who attack me online players?

A: No, not yet if you're just starting the game. The enemies you encounter are NPCs controlled by AI (Artificial Intelligence).

Q: I want to craft Berry Tea or other items, but nothing happens. Why?

A: That usually happens when you haven't added enough materials to the Campfire or Melting Furnace. Make sure all required ingredients are placed correctly.

Q: Is it true that opening a Weapon Crate from the Dealer during an Airdrop always gives you a firearm?

A: No, that's just a myth. I've tested it myself—sometimes you get guns, sometimes you don’t. It’s random.

That's it for our Last Day on Earth: Survival Wiki Guide! If you spot any outdated or incorrect information, I’ll update it as soon as possible. Have tips or tricks to share? Drop them in the comments below. Thanks for reading!

Read also: Top 5 YouTube Channels You Should Watch If You Play Last Day on Earth